Щоб переглянути інші типи публікацій з цієї теми, перейдіть за посиланням: Spin polarized electron gas.
Дисертації з теми "Spin polarized electron gas"
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся з топ-50 дисертацій для дослідження на тему "Spin polarized electron gas".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Переглядайте дисертації для різних дисциплін та оформлюйте правильно вашу бібліографію.
1
Kato, Takashi, Yasuhito Ishikawa, Hiroyoshi Itoh, and Jun-ichiro Inoue. "Intrinsic anisotropic magnetoresistance in spin-polarized two-dimensional electron gas with Rashba spin-orbit interaction." American Physical Society, 2008. http://hdl.handle.net/2237/11252.
Повний текст джерела
2
Zhou, Haosheng. "Theory of the magnetic resonance spectrum of spin-polarized hydrogen gas." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26678.
Повний текст джерелаАнотація:
The Green's function method is applied to investigate the magnetic spin resonance spectra of three-dimensional and two-dimensional spin-polarized quantum gases.
The Hartree-Fock approximation is employed to calculate the one-particle Green's function of the atoms, then this one-particle Green's function is used for the calculation of the vertex part of the Green's function. Such a combination yields a self-consistent result. The absorption spectra are obtained from the calculation of the susceptibility in terms of the two-particle Green's function (bubble diagram). Some general expressions for the dispersion relation, for the effective mass of a spin wave, and for the dipolar frequency shift are given in the calculation.
In order to estimate the shift of the electron-spin-resonance (ESR) frequency, the effective dipole-dipole interactions among the hydrogen atoms are included in the calculation. These effective interactions are deduced from the ladder approximation, and hence are characterized by the scattering amplitude. The scattering amplitude is calculated numerically. The result shows that the theoretical value of the shift is smaller than the experimentally observed value by about 35%.Science, Faculty of
Physics and Astronomy, Department of
Graduate
3
Sadeghzadeh, Kayvan. "Spin polarised Fermi gases." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610744.
Повний текст джерела
4
Yokoyama, Koji. "Muon probes of spin-polarized electrons in GaAs." Diss., UC access only, 2009. http://proquest.umi.com/pqdweb?index=104&did=1907186881&SrchMode=1&sid=1&Fmt=7&retrieveGroup=0&VType=PQD&VInst=PROD&RQT=309&VName=PQD&TS=1270484411&clientId=48051.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--University of California, Riverside, 2009.Includes abstract. Includes bibliographical references (leaves 121-123). Issued in print and online. Available via ProQuest Digital Dissertations.
5
Kuwahara, M., T. Morino, T. Nakanishi, S. Okumi, M. Yamamoto, M. Miyamoto, N. Yamamoto, et al. "Spin-Polarized Electrons Extracted from GaAs Tips using Field Emission." American Institite of Physics, 2007. http://hdl.handle.net/2237/11993.
Повний текст джерела
6
Gröbli, Jean-Claude. "Spin filter and highly polarized electron sources /." [S.l.] : [s.n.], 1995. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=11148.
Повний текст джерела
7
Hatton, D. C. "Spin polarized electron scattering at ferromagnetic interfaces." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603854.
Повний текст джерела
8
Allenspach, Rolf Allenspach Rolf Allenspach Rolf Allenspach Rolf. "Magnetic characterization at surfaces by spin polarized electron spectroscopies /." [S.l.] : [s.n.], 1985. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=7952.
Повний текст джерела
9
Buckle, S. J. "Molecular field effects in electron spin polarized atomic deuterium." Thesis, University of Sussex, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372071.
Повний текст джерела
10
Mohamad, Haidar Jawad. "Ultrafast optical measurements of spin-polarized electron dynamics in nanostructured magnetic materials." Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/18425.
Повний текст джерелаАнотація:
At present, electronic devices depend upon electric charge to transfer and record information. However, such devices are approaching a scaling limit due to Joule heating. Spintronics offers a solution by exploiting the spin rather than the charge of the electron, since the propagation of spin current can in principle occur without dissipation. Immediate applications lie in magnetic random access memory and novel media for hard disk recording. Within this thesis, the Magneto-optical Kerr effect (MOKE) has been used to measure the static and dynamic magnetic properties of a number of different thin film samples that are of interest for spintronic applications. A femtosecond laser has been used to perform time-resolved MOKE (TRMOKE) and time resolved reflectivity (TRR) measurements simultaneously, which probe the spin and charge dynamics respectively. Measurements have been performed upon a continuous thin film of CrO2 that is known to be half-metallic in bulk form, and a series of YIG/Cu/Ni81Fe19 based structures that are expected to exhibit the spin Seebeck effect (SSE). Chemical vapour deposition (CVD) was used to fabricate the continuous CrO2 thin film on a (100)-oriented TiO2 substrate. Precessional magnetisation dynamics were studied by means of the TRMOKE technique. The dependence of the precession frequency and the effective damping parameter upon the static applied magnetic field were investigated. The precession frequency exhibited a minimum at the hard axis saturation field as expected. However precession was also observed for fields greater than the hard axis saturation value, perhaps suggesting the presence of a twisted magnetic state within the film. TRMOKE and TRR measurements were performed upon the YIG/Cu/Ni81Fe19 based structures for different values of the pump fluence and applied magnetic field. For fixed pump fluence and varying applied field, the frequency of precession is well described by a numerical solution of the Landau-Lifshitz equation for the Ni81Fe19 (permalloy, Py) layer. The frequency, amplitude, damping, phase and chirp of the precessional oscillations was extracted from measurements made with a field of 3 kOe applied at 2.8° from the normal to the sample plane, in a configuration designed to maximise any spin transfer torque (STT) generated by the SSE. The oscillation parameters extracted for trilayer samples and a Py reference sample were found to be very similar. Features indicative of STT predicted by simulations were not observed. This suggests that either the YIG/Cu interface was unable to efficiently transmit spin current within the samples studied here, or else that the STT generated by means of the SSE is too small to be of practical use.
11
Okumi, Shoji, Naoto Yamamoto, Kuniaki Tamagaki, Atsushi Mano, Ryosuke Sakai, Masahiro Yamamoto, Makoto Kuwahara, et al. "Development of the New Type Polarized Electron Source for SPLEEM." American Institite of Physics, 2007. http://hdl.handle.net/2237/11990.
Повний текст джерела
12
Djeghloul, Fatima Zohra. "Study of organic semiconductor / ferromagnet interfaces by spin-polarized electron scattering and photoemission." Phd thesis, Université de Strasbourg, 2013. http://tel.archives-ouvertes.fr/tel-01062352.
Повний текст джерелаАнотація:
I studied organic semiconductor/ferromagnet interfaces by characterizing them by spin-polarized electron scattering and photoemission spectroscopy experiments. In the first part, a completely unexpected behaviour of the spin-dependent electron reflection properties of these interfaces is observed. In fact, sub-monolayer coverage of the organic molecules makes the electron reflection amplitude independent of the spin, i.e. both the reflectivity and the reflection phase become independent of the spin orientation of the incident electrons. Although I am not able at the moment to identify the cause of this phenomenon, I show that it is a very general phenomenon which is independent of the energy of the primary electrons, the choice of the ferromagnetic substrate, the choice of the organic molecule, and of the orientation of the initial spin polarization. It is not due to a change of the surface magnetization, a depolarization of the primary electrons, or a direct interaction of the molecules with the ferromagnetic substrate. Moreover, theory does not predict so far the experimental results and further research is required to unveil the physics behind these observations. In the second part of my thesis, spin-resolved photoemission experiments have been performed at the synchrotron SOLEIL. The main result is the observation of a highly spin-polarized molecule-induced electronic state close to the Fermi level. Measurements as a function of the organic layer thickness allow us to determine the interfacial character of this electronic state. Finally, these results are compared with theoretical calculations performed at the institute.
13
Lindebaum, Stephan [Verfasser], Jürgen [Akademischer Betreuer] König, and Wolfgang [Akademischer Betreuer] Belzig. "Spin-Polarized Transport in Single-Electron Spin-Valve Transistors / Stephan Lindebaum. Gutachter: Wolfgang Belzig. Betreuer: Jürgen König." Duisburg, 2012. http://d-nb.info/1036115887/34.
Повний текст джерела
14
Went, Michael Ray, and n/a. "Scattering of Spin Polarized Electrons from Heavy Atoms: Krypton and Rubidium." Griffith University. School of Science, 2003. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20040220.134142.
Повний текст джерелаАнотація:
This thesis presents a set of measurements of spin asymmetries from the heavy atoms krypton and rubidium. These investigations allow examination of the spin orbit interaction for electron scattering from the target atoms. These measurements utilise spin polarized electrons in a crossed beam experiment to measure the Sherman function from krypton and the A2 parameter from the 52P state of rubidium. The measurements utilise a new spin polarized electron energy spectrometer which is designed to operate in the 20-200 eV range. The apparatus consists of a standard gallium arsenide polarized electron source, a 180 degrees hemispherical electron analyser to detect scattered electrons and a Mott detector to measure electron polarization. A series of measurements of the elastic Sherman function were performed on krypton at incident electron energies of 20, 50, 60, 65, 100, 150 and 200 eV. Scattered electrons are measured over an angular range of 30-130 degrees. These measurements are compared with calculations of the Sherman function which are obtained by solution of the Dirac-Fock equations. These calculations include potentials to account for dynamic polarization and loss of flux into inelastic channels. At the energies 50, 60 and 65 eV, experimental agreement with theory is seen to be extremely dependent on the theoretical model used. Measurement of the A2 parameter from the combined 52P1/2,3/2 state of rubidium are performed at an incident energy of 20 eV. The scattered electrons are measured over an angular range of 30-110 degrees. This measurement represents the first such measurement of this parameter for rubidium. Agreement with preliminary calculations performed using the R-matrix technique are good and are expected to improve with further theoretical development.
15
Riley, Susan Tania. "Combined two-dimensional electron gas and artificial spin ice structures." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/13973/.
Повний текст джерелаАнотація:
This thesis presents research into the electron transport properties of hybrid semiconductor / ferromagnetic structures. Periodic arrays of ferromagnetic stripes and artificial spin ice (ASI - arrays of geometrically frustrated nanomagnets) are patterned atop GaAs-AlGaAs wafers containing a two-dimensional electron gas (2DEG), and resistance measurements are performed under cryogenic temperatures and applied magnetic fields. The effects of piezoelectric strain on the transport properties of 2DEGs are investigated by comparing the resistances of magnetic and non-magnetic stripes patterned atop a 2DEG. Piezoelectric strain manifests itself as electric commensurability oscillations in the longitudinal resistance of a 2DEG. These oscillations are independent of temperature and are caused by stress acting upon the edges of the stripes. Transport measurements of combined 2DEG / ASI structures reveal the first observations of commensurability oscillations (COs) caused by ASI in the longitudinal resistance of a 2DEG. These oscillations are periodic on length-scales commensurate with the length of the individual nanomagnets that form the ASI. The COs are temperature dependent, but independent of the angle of applied magnetic field for our particular samples. Models based upon a Fourier analysis of Maxwell's equations help explain our results. This thesis also addresses the thermally-activated magnetization dynamics behaviour of ASI. We show exactly how the proportion of each vertex type changes as an ASI is heated, and moves from an ordered state to a ground state. We compare the results from two different alloys of PdFe and three different lattice spacings. The way in which arrays of ASI change to a ground state is dependent upon the material composition of the ASI, with little dependence upon the period of the ASI. A material with a large magnetization requires a higher temperature to cause any magnetic spins to flip, after which the ASI abruptly changes from an ordered state to a ground state.
16
Haidar, Mohammad. "Role of surfaces in magnetization dynamics and spin polarized transport : a spin wave study." Phd thesis, Université de Strasbourg, 2012. http://tel.archives-ouvertes.fr/tel-00869643.
Повний текст джерелаАнотація:
In this thesis, the interplay between electron transport and magnetization dynamics is explored in order to access to fundamental properties of ferromag- netic metal thin films. With the aim of extracting the influence of the electron surface scattering on the spin-dependent resistivities, thickness series of permal-loy (Ni80Fe20) films were grown and studied. In addition to standard electrical and magnetic measurements, a detailed study of the propagation of spin waves along these films was performed. Resorting to the current-induced spin-wave Doppler shift technique, the degree of spin-polarization of the electrical current was extracted. This degree of spin-polarization was found to decrease when the film thickness decreases, which suggests that the film surfaces contribute to the spin dependent resistivities and tend to depolarize the electrical current.
17
Schepper, Dirk De 1968. "Spin-dependent deep inelastic positron scattering from a polarized helium-3 internal gas target." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/46066.
Повний текст джерела
18
Seemann, Klaus Michael. "Spin polarized electron transport and the anomalous Hall effect in L10-ordered epitaxial Fe-alloys." Thesis, University of Leeds, 2009. http://etheses.whiterose.ac.uk/115/.
Повний текст джерелаАнотація:
Two epitaxial ferromagnets FePd and its isoelectronic partner FePt, which order in the well known face-centered tetragonal L10-phase, have been fabricated to (a) evaluate the current spin polarization in the ballistic and in the diffusive electron transport regime, (b) to elucidate whether there is a discrepancy in the current spin polarizations depending on the transport regime, how high this discrepancy is, and finally (c) how the spin-orbit scattering strength changes by replacing Pd by Pt. These are questions of fundamental importance in the field of electron transport studies in magnetic materials, in the recent years known as spintronics. The study began with experimental investigations on the structural, magnetic, and electron transport properties of a L10-ordered epitaxial iron-platinum (FePt) alloy layer fabricated by magnetron-sputtering on a single-crystal MgO(001) substrate. At all temperatures ranging from 2 K to 258 K, a diffusive spin current polarization of > 80% was found. To study the ballistic transport regime, point-contact Andreev-reflection measurements at 4.2 K were performed and a value for the ballistic current spin polarization of ∼ 42% was obtained (which compares very well with that of a polycrystalline thin film of elemental Fe). This discrepancy is attributed to a difference in the characteristic scattering times for oppositely spin-polarized electrons, such scattering times influencing the diffusive but not the ballistic current spin polarization. One of the main parameters in the L10-phase ferromagnets is the degree of crystallographic long range ordering. To investigate the influence of the long range ordering on the current spin-polarization, epitaxial FePd magnetic thin films of varying degrees of L10-phase chemical order were used. By quantitatively accounting for changes in micromagnetism through simulation and magnetic force microscopy, it is shown within the Levy-Zhang spin-mistracking theory of domain wall resistance, that this is connected to a change in the average degree of spin-dependence at the scattering centers that control the diffusive transport in this system, suggesting a possible means of producing highly spin-polarized currents in the diffusive electron transport regime. Finally, both materials L10-FePd and -FePt were investigated with respect to the anomalous Hall effect as a consequence of spin-orbit scattering. A linear dependence between transverse and longitudinal resistivity in epitaxial L10- ordered FePd and FePt films due to the anomalous Hall effect (AHE) has been observed. In ordered ferromagnets such a linear relation may be anticipated due to the skew-scattering mechanism; the absence of an additional quadratic term suggests that side-jump scattering, which is dominant in less well ordered material, has been effectively suppressed. One finds that on exchanging Pd for the heavier, though isoelectronic Pt, the skew-scattering deflection angle in an individual electronic scattering event dramatically increases from 17 to 49 mrad. This increase corresponds well to a Z3/2 dependence of the atomic spin-orbit interaction energy, contrary to commonly assumed Z4 dependence.
19
Inoue, Jun-ichiro, Takashi Kato, Yasuhito Ishikawa, and Hiroyoshi Itoh. "Vertex Corrections to the Anomalous Hall Effect in Spin-Polarized Two-Dimensional Electron Gases with a Rashba Spin-Orbit Interaction." The American Physical Society, 2006. http://hdl.handle.net/2237/7131.
Повний текст джерела
20
Lerescu, Alexandru Ionuţ. "Spin and charge transport in a gated two dimensional electron gas." [S.l. : Groningen : s.n. ; University Library Groningen] [Host], 2007. http://irs.ub.rug.nl/ppn/304671568.
Повний текст джерела
21
Manoli, Soheil Dimitri. "The generalized exchange local spin density-functional theory /." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75359.
Повний текст джерелаАнотація:
An orbital dependent local spin density-functional (LSD) scheme with a generated exchange, the LSD GX scheme, has been developed based on the correct normalization conditions of an electron gas. This scheme contains no adjustable parameters; the B$ sb1$, B$ sb2$ and $ alpha sp lim$ are constant for all atoms once the shape of the Fermi hole is chosen. These parameters are rigorously calculated using an unspecified Fermi hole correlation factor and they give an exchange density which reduces exactly to the homogeneous free electron gas one at the high electron density limit.The LSD GX exchange density is corrected for self-interaction (SI) by splitting the total Fermi hole correlation factor into pure-exchange and self-interaction holes.
These new LSD and SI corrected schemes are compared to each other. They also compare very well theoretically and numerically (total energies and eigenvalues) with other local schemes current in the literature.
New equations for the IP and electronegativities of the atoms in these local schemes are derived which give good results.
22
Inoue, Jun-ichiro, Gerrit E. W. Bauer, and Laurens W. Molenkamp. "Diffuse transport and spin accumulation in a Rashba two-dimensional electron gas." The American Physical Society, 2003. http://hdl.handle.net/2237/7111.
Повний текст джерела
23
Nunner, Tamara S., N. A. Sinitsyn, Mario F. Borunda, V. K. Dugaev, A. A. Kovalev, Ar Abanov, Carsten Timm, et al. "Anomalous Hall effect in a two-dimensional electron gas." American Physical Society, 2007. http://hdl.handle.net/2237/11243.
Повний текст джерела
24
Yu, Wing Wa. "Low temperature spintronics : probing charge and spin states with two-dimensional electron gas." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/12580.
Повний текст джерелаАнотація:
This thesis is based on two low temperature experiments in spintronics - physics and engineering of electronic spins. The measurements were performed on a GaAs/AlGaAs two-dimensional electron gas with geometries defined by tunable surface gates. The first experiment is about detection of electrons in a quantum dot. A quantum point contact (QPC) and a quantum wire (QW) is coupled to a single-lead few-electron quantum dot. By measuring the conductance of the QPC and the QW, one can gain information on the average number of electrons in the dot as well as energy-level structure of the dot. The second experiment investigates anisotropy of spin-orbit interaction in GaAs/AlGaAs heterostructure by measuring spin polarization in a narrow channel. Polarized electrons are injected into the channel through a spin-selective injector QPC and diffuse towards the end of the channel. This diffusion generates a pure spin current and the spin polarization 25 microns away is measured by a detector QPC. A periodic spin-orbit field induced by motion of the electrons in the channel causes the spins to resonate with external magnetic field. Spin-orbit anisotropy is demonstrated by the different resonance strength observed in channels aligned along two different crystal axes.
25
Ebrahimnejad, Rahbari Seyed Hadi. "Electrical measurement of spin-dependent resistivity in GaAs/AlGaAs two-dimensional electron gas." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/13900.
Повний текст джерелаАнотація:
The electrical transport in the semiconductor two-dimensional electron gases
(2DEGs) in the presence of magnetic fields have been the subject of extensive
experimental and theoretical studies. Whereas the experiments generally
focus on the total magnetotransport of the spin-up and spin-down
electrons, the problem of how individual spin components contribute to the
sum has been mostly remained untouched. Due to the Zeeman splitting of
the Fermi velocities, spin-up and spin-down electrons face different resistivities
against their flow. In this thesis, this problem is addressed based on
electrical generation and detection of nonequilibrium spin polarization in a
narrow conducting channel of 2DEG in a GaAs/AlGaAs heterostructure. It
makes use of narrow quasi-one-dimensional constrictions, known as quantum
point contacts (QPCs), at a high magnetic field as the injector and
detector of the spin polarization. We also simulate the problem based on
an one-dimensional spin diffusion model and it turns out that it numerically
agrees with the measurements using an electron spin susceptibility which is
enhanced compared to that of bare GaAs. Such enhancements are generally
linked with the electron-electron interactions which become important for
electrons in confined geometries.
The first section reviews the general characteristic properties of 2DEGs
in GaAs/AlGaAs semiconductor heterostructures, gate-defined structures
and quantized electrical transport through QPCs. The second chapter reviews
the main results of electronic transport measurements on 2DEGs in
the presence of in-plane magnetic fields, and the third chapter includes our
spin polarization measurement results in a narrow channel of 2DEG and
how they help to account for the effect of spin orientation on the electrical
resistivity.
26
Yuan, Junhua Filippone Bradley. "Progress towards a high precision measurement of the neutron spin--electron angular correlation in polarized neutron beta decay with ultra-cold neutrons /." Diss., Pasadena, Calif. : Caltech, 2006. http://resolver.caltech.edu/CaltechETD:etd-01302006-153024.
Повний текст джерела
27
Castro, Vaz Diogo. "Spin-to-charge current conversion in SrTiO3-based two-dimensional electron gases." Electronic Thesis or Diss., Sorbonne université, 2018. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2018SORUS449.pdf.
Повний текст джерелаАнотація:
Ce travail présente l’étude de la conversion courant de spin en courant de charge dans les gaz d’électrons bidimensionnels à base de SrTiO3. Nous commençons par une présentation des concepts de base de la spintronique : le spin, une définition du courant de spin et le comportement des spins dans des matériaux, les principales conséquences de la relation entre les courants de charge et de spin dans différents matériaux, et comment un courant de charge peut être converti en un courant de spin (et vice versa). Dans des scénarios spécifiques, la physique de l’interconversion suit des considérations de symétrie particulières dans le cadre des effets de Dressllehaus et de Rashba, qui expliquent l’interconversion du courant de charge/spin dans les gaz d’électrons 2D via l’effet direct et inverse d’Edelstein. Dans le deuxième chapitre, nous présentons le principal matériau utilisé dans cette thèse: le titanate de strontium (SrTiO3). Après avoir analysé ses principales caractéristiques, nous explorons le gaz d’électrons 2D présent dans le système LaAlO3/SrTiO3. Nous discutons en détail de l’origine de la conductivité interfaciale entre ces deux isolateurs, l’épaisseur critique de conduction de 4 mailles de LaAlO3 et des principaux mécanismes conduisant à la formation du gaz électronique 2D (catastrophe polaire, interdiffusion de cation, réactions à la surface et défauts induits par la polarité). Ensuite, nous décrivons en détail la procédure expérimentale pour obtenir des hétérostructures de LaAlO3/SrTiO3: le traitement de surface des monocristaux de SrTiO3, la croissance par ablation laser pulsé de films ultra-minces de LaAlO3, et la pulvérisation cathodique. Nous introduisons les deux techniques principales utilisées pour évaluer les propriétés interfaciales, la spectroscopie photoélectronique de rayons X (XPS) et le magnétotransport, avec quelques résultats pour les échantillons de LaAlO3/SrTiO3. Enfin, nous montrons comment un mince dépôt d’une couche métallique sur LaAlO3/SrTiO3 peut modifier radicalement les propriétés interfaciales en réduisant (si le métal est réactif et possède un travail de sortie inférieur à une valeur critique) ou en augmentant (pour les métaux nobles) l’épaisseur critique de la conduction interfacial. Pour conclure ce chapitre, nous proposons un modèle qui décrit comment un gaz d’électrons 2D peut être créé dans d’autres systèmes à base d’oxydes complexes. Dans le troisième chapitre, nous étudions les phénomènes de conversion spin/charge. Nous commençons par un état de l’art de la littérature concernant des observations expérimentales des gaz d’électrons Rashba 2D, ainsi que de la conversion du courant spin-à-charge par l’effet Edelstein inverse dans les puit de potentiel à base de semi-conducteurs, les isolants topologiques et les systèmes à base d’oxydes. Ensuite, nous introduisons le pompage de spin, une technique utilisée pour générer des courants de spin purs. Les résultats de la conversion du courant spinà-charge dans les systèmes LaAlO3/SrTiO3 et metal/SrTiO3 sont présentés, accompagnés d’une interprétation de la géante et ajustable con-version spin/charge. Dans le cas d’échantillons composés par metal/SrTiO3 , la spectroscopie photoélectronique résolue en angle (ARPES) et les notions de mélange de bande électronique et de topologie sont introduites pour justifier la conversion charge/spin extrêmement élevé. Dans le dernier chapitre, nous montrons des expériences supplémentaires réalisées sur le système LaAlO3/SrTiO3 en ce qui concerne la magnétorésistance anisotrope et unidirectionnelle [...]This thesis is composed by four chapters. In the first, we start by introducing basic concepts in spintronics, such as the electron spin, a definition of spin current, and how spins behave in real materials. Then, we review the main consequences of the relation between charge and spin currents in different materials, and how a charge current can be converted in a spin current (and vice-versa). In particular scenarios, the physics of the interconversion follows special symmetry considerations in the framework of the Dressllehaus and Rashba effects, which in turn explain the spin-to-charge current interconversion in 2D electron gases through the direct and inverse Edelstein effect. In the second chapter, we introduce the main material used throughout this thesis: strontium titanate (SrTiO3). After reviewing its main features, we explore the remarkable 2D elec-tron gas found in the LaAlO3/SrTiO3 system. We discuss in detail the origin of the interfacial conductivity that arises between these two insulators, the critical thickness for conduction of 4 unit cells of LaAlO3, and the main mechanisms that lead to the 2D electron gas formation (polar catastrophe, cation interdiffusion, surface reactions and polarity-induced defects). Then, we thoroughly describe the experimental procedure to obtain such heterostructures, including a comprehensive guide on the surface treatment of SrTiO3 single crystals, the pulsed laser deposition growth of ultra-thin LaAlO3 films and magnetron sputtering. In addition, we elaborate on the two main techniques used to evaluate the interfacial properties, X-ray photoelectron spectroscopy and magnetotransport, while showing some results for LaAlO3/SrTiO3 samples. Lastly, we show how a thin deposition of a metallic layer on top of LaAlO3/SrTiO3 can drastically change the interfacial properties, by reducing (if the metal is reactive) or increasing (for noble metals) the critical thickness for conduction. We end this chapter by giving a blueprint that describes how a 2D electron gas can be created in other oxide systems. In the third chapter we investigate spin-tocharge conversion phenomena. We start by giving an overview on experimental observations of Rashba 2D electron gases, as well as spin-to-charge current conversion through the inverse Edelstein effect in semiconductor quantum wells, topological insulators and oxide-based systems. Then, we thoroughly introduce spin pumping, a technique used to generate pure spin currents. Results for spin-to-charge current conversion in the LaAlO3/SrTiO3 and metal-capped SrTiO3 systems are shown, accompanied by an interpretation of the large and tunable conversion efficiency. For the metal-capped SrTiO3 case, angle-resolved photoemission spectroscopy and notions of electronic band mixing and topology are introduced to describe the extremely large efficiency. In the last chapter, we show additional experiments performed on the LaAlO3/SrTiO3 system regarding anisotropic and unidirectional magnetoresistance, while reviewing the scarce bibliography on these effects in 2D electron gases. After that, we introduce a recently discovered effect, the unidirectional spin Hall magnetoresistance, and develop a simple conceptual model for an analogous effect in 2D electron gases: the unidirectional Edesltein magnetoresistance. This effect is based on the expected strong charge-to-spin conversion in 2D electrons gas, and the interaction of the generated spin currents with an adjacent ferromagnet. We finish by very briefly showing preliminary experiments in NiFe/ LaAlO3/SrTiO3 heterostructures
28
Nilwala, Gamaralalage Premasiri Kasun Viraj Madusanka. "Electron Transport in Chalcogenide Nanostructures." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1572259784431038.
Повний текст джерела
29
Evaldsson, Martin. "Quantum transport and spin effects in lateral semiconductor nanostructures and graphene." Doctoral thesis, Norrköping : Department of Science and technology, Linköping University, 2008. http://www.bibl.liu.se/liupubl/disp/disp2008/tek1202s.pdf.
Повний текст джерела
30
Krishtopenko, Sergey. "Spin splitting and collective effects in InAs/AlSb quantum well heterostructures." Toulouse 3, 2011. http://thesesups.ups-tlse.fr/1459/.
Повний текст джерелаАнотація:
Les travaux de cette thèse, essentiellement théorique, concernent l'étude des phénomènes dépendants du spin, à un électron et à n-corps, dans les puits quantiques (PQ) de semiconducteurs (SC) à faible gap InAs/AlSb. Les résultats obtenus permettent de prévoir de nouveaux effets physiques, ils sont comparés aux résultats expérimentaux existants. L'asymétrie du champ électrique aux interfaces InAs/AlSb est étudiée expérimentalement et théoriquement, son effet sur le spectre d'énergie des sous bandes électriques est mis en évidence. La possibilité de contrôler optiquement ce champ électrique, et par là le clivage de spin par effet Rashba sous champ magnétique nul, est démontrée. La prise en compte des interactions e-e sur les niveaux de Landau des quasi-particules ainsi que sur la densité d'états au niveau de Fermi est réalisée dans ce système pour la première fois. Le calcul théorique de l'exaltation du facteur g par échange dans les puits quantiques à faible gap est développé. Le calcul permet de prédire l'évolution du facteur g "magnéto-optique" dans les hétérostructures InAs/AlSb déterminé par résonance de spin, il met en évidence la violation du théorème de Larmor dans les hétérostructures à base de SC à faible gap. L'étude théorique de la résonance cyclotron, en régime quantique, d'un gaz bidimensionnel d'électrons de haute mobilité démontre aussi la violation du théorème de Kohn dans les hétérostructures InAs/AlSb. Les résultats obtenus dans ce travail de thèse apportent des informations utiles pour le "design" et la mise au point de nouveaux dispositifs électroniques ou optoélectroniques basés sur des hétérostructures InAs/AlSbThe Thesis is devoted to the study of "single-particle" and "many-body" spin-related phenomena in narrow-gap InAs/AlSb quantum well (QW) heterostructures. The scientific significance of the results obtained consists in the discovering and prediction of new physical effects. The asymmetry of the built-in electric field in InAs/AlSb QW heterostructures has been probed both experimentally and theoretically and its effect on the electron energy spectrum splitting in electric subbands is demonstrated. A principle possibility to control by optical means the "built-in" electric field and the Rashba spin splitting in zero magnetic field is exhibited. The theoretical investigation into e-e interaction effect on quasiparticle Landau levels and density-of-states at the Fermi level is undertaken for the first time. Theory of the exchange enhancement of quasiparticle g-factor in narrow gap QW heterostructures is developed in the Thesis. Calculation results on the "magnetooptical" g-factor in InAs/AlSb heterostructure measured in electron spin resonance are the first demonstration of Larmor theorem violation in narrow gap QW heterostructures. Cyclotron resonance study in the samples with high mobility 2D electron gas in quantizing magnetic fields provides evidences of Kohn theorem violation in InAs/AlSb heterostructures. The results obtained in the Thesis can be utilized at the designing new electronic and optoelectronic units as well the spintronic devices based on InAs/AlSb heterostructures
31
Ayllon, Edgar Fernando Aliaga. "O transistor válvula de spin de AlGaAs/GaAs e outros semicondutores: dirigido a novos dispositivos spintrônicos." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-20102014-164755/.
Повний текст джерелаАнотація:
Neste trabalho, apresentamos estudos de magnetotransporte em um sistema quase tridimensional de elétrons produzido em amostras contendo poços quânticos parabólicos (PQW, Parabolic Quantum Well ) formados em heteroestruturas de AlGaAs crescidos sobre substratos de GaAs pela técnica de epitaxia por feixe molecular (MBE). Na primeira parte do nosso trabalho realizamos medidas de magnetoresistência, efeito Hall e efeito Shubnikov-de Haas em PQWs com larguras de 1000 Å a fim de investigar as propriedades eletronicas tais como a concentração e a mobilidade dos elétrons nas amostras. Através de cálculos autoconsistentes determinou-se os perfis de potencial, os níveis de energia e as concentrações de cada uma das sub-bandas ocupadas no poço. Uma análise através da transformada de Fourier também permitiu determinar as concentrações eletrônicas nas sub-bandas. Em uma segunda parte estudou-se a influência da aplicação de potenciais externos através de uma porta metálica com barreira em uma amostra contendo um PQW de largura 3000 Å na presença de campos magnéticos perpendicular e paralelo à superfície da amostra. Encontrou-se que para uma tensão de porta de Vg = 0, 55V forma-se uma barreira de potencial ainda sem ter depleção de cargas no poço. Apresenta-se a idealização do dispositivo transistor válvula de spin, a partir do fato que aplicando uma tensão de porta é possível deslocar espacialmente os elétrons e mudar a sua orientaçãp de spin.Results from magnetic transport studies made on quasi-three-dimensional electron systems are presented in this work. AlGaAs heterostructures grown on GaAs subtrates through molecular beam epitaxy (MBE) enable the existence of this type of systems by means of parabolic quantum wells (PQW) formation. This work was developed in two main parts. First, we studied magnetoresistence phenomena, such as Hall effect and Shubnikov-de Haas, on 1000 Å width PQWs. This permits to know the electronic concentration and mobility values of this type of samples, among other electrical properties. Then, self-consistent calculations gave an outline of the size and shape of the potentials, and gave the values for the energy levels and the electronic concentration on each occupied sub-band of the quantum well. Through Fourier transform analysis was also possible to obtain and confirm the electronic concentrations of the occupied sub-bands. In the second part of the work, we studied the effects of applying an external potential through a barrier gate to a 3000 Å width PQW sample in the presence of magnetic fields parallel and perpendicular to the sample surface. For a V g = 0, 55 V gate voltage, it was found that a potential barrier was formed even without charge depletion in the well. An idealization for the spin valve transistor device, based on the fact that applying a gate potential spatially dislocates the electrons and changes their spin orientation, is presented.
32
Tastevin, Geneviève. "Helium trois polarise : ondes de spin et liquefaction du gaz." Paris 6, 1987. http://www.theses.fr/1987PA066114.
Повний текст джерелаАнотація:
Observation de l'apparition de modes oscillants amortis, ondes de spin, pour la diffusion d'aimantation dans l'helium 3 gazeux polarise par pompage optique, dans l'intervalle 2-6k; bon accord entre les mesures du coefficient caracterisant la surtension de ces ondes et des calculs numeriques ab initio a partir du potentiel interatomique he-he. Mise au point d'une technique de condensation rapide de **(3)he oriente permettant d'obtenir un echantillon liquide a spin polarise; etude rmn de l'aimantation du systeme liquide-gaz a l'equilibre
33
Grenier, Philippe. "Etude des fonctions de structure en spin du nucleon : l'experience e143 au slac." Clermont-Ferrand 2, 1995. http://www.theses.fr/1995CLF21720.
Повний текст джерелаАнотація:
Cette these decrit l'experience e143 de diffusion profondement inelastique d'electrons de 29 gev sur des cibles de nh#3 et nd#3 polarisees. Elle s'est deroulee aupres de l'accelerateur de stanford, en californie, et son but etait de mesurer les fonctions de structure polarisees g#1 et g#2 sur le proton et le deuton. Ces fonctions de structure permettent de tester la regle de somme de bjrken, regle fondamentale de la chromodynamique quantique. Elles nous renseignent egalement sur la structure en spin du nucleon et, en particulier, elles permettent d'acceder a la fraction du spin du nucleon portee par les quarks. Experimentalement, on determine les fonctions de structure par la mesure d'asymetries en sections efficaces. Nous obtenons pour le premier moment de g#1, pour le proton et le deuton, des valeurs qui se situent de deux a trois deviations standards en dessous des predictions d'ellis et jaffe, mais nos resultats confirment la validite de la regle de somme de bjrken et permettent d'estimer a environ 30% la contribution des quarks au spin du nucleon. Nos resultats sur g#2 semblent etre bien decrits par l'expression de wandzura et wilczek
34
Yan, Zeyin. "Reconstruction de densité d'impulsion et détermination de la matrice densité réduite à un électron." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLC001/document.
Повний текст джерелаАнотація:
La diffraction des rayons X à haute résolution (XRD) et celle des neutrons polarisés (PND) sont couramment utilisées pour modéliser les densités de charge et de spin dans l'espace des positions. Par ailleurs, la diffusion Compton et diffusion Compton magnétiques sont utilisées pour observer les plus diffus des électrons appariés et non appariés, en fournissant les profils Compton directionnels de charge (DCPs) et les profils Compton magnétique directionnels (DMCPs). Il est possible d'utiliser plusieurs DCPs et DMCPs non équivalents pour reconstituer la densité d'impulsion à deux ou trois dimensions. Puisque toutes ces techniques décrivent les mêmes électrons dans différentes représentations, nous nous concentrons sur l'association de la densité d'impulsion, reconstituée par DCPs (DMCPs) avec la densité de charge et spin, telle que déterminée à parties données XRD (PND).La confrontation théorie-experience, ou --plus rarement-- entre différentes techniques expérimentales, requièrent généralement les representations des densités reconstruites dans les espaces des positions et des impulsions. Le défi que pose la comparaison des résultats obtenus par calculs ab-initio et par des approches expérimentales (dans le cas de Nit(SMe)Ph) montre la nécessité de combiner plusieurs expériences et celle d'améliorer les modèles sur lesquels reposent les approches théoriques. Nous montrons que, dans le cas d'une densité de probabilité de présence d'électrons résolue en spin, une approche simple de type Hartree-Fock ou DFT ne suffit pas. Dans le cas de YTiO3, une analyse conjointe des espaces position et impulsion (PND & MCS) met en évidence un possible couplage ferromagnétique selon Ti--O1-Ti. Pour cela, une densité magnétique de "super-position" est proposée et s'avère permettre une vérification aisée de la cohérence entre densité de charge (spin) et densité de 'impulsion déterminées expérimentalement, sans la nécessité d'une étape ab-initio. Pour aller plus loin, un modèle "de Ti isolé", basé sur des coefficients orbitaux affinés par PND, souligne l'importance du couplage cohérent métal-oxygène nécessaire à rendre compte des observations dans l'espace des impulsions.La matrice densité réduite à un électron (1-RDM) est proposée comme socle de base permettant de systématiquement combiner les espaces des positions et des impulsions. Pour reconstruire cette 1-RDM à partir d'un calcul ab-initio périodique, une approche "cluster" est proposée. Il devient alors possible d'obtenir la 1-RDM théorique résolue en spin sur des chemins de liaison chimique particuliers. Ceci nous permet notamment de clarifier la différence entre les couplages Ti--O1--Ti et Ti-O2--Ti. Il est montré que l'importance des contributions du terme d'interaction entre les atomes (de métal et d'oxygène) est différente selon que l'on considère une représentation des propriétés dans l'espace des positions ou des impulsions. Ceci est clairement observé dans les liaisons chimiques métal-oxygène et peut être illustré par une analyse séparant les contributions par orbitales. Les grandeurs decrivant les électrons dans l'espace des phases comme la fonction de Moyal peuvent également être déterminées par cette construction en "cluster". Ceci peut revêtir un intérêt particulier si la technique de diffusion Compton aux positions de Bragg pouvait être généralisée. Les premiers résultats d'un affinement de modèle simple de 1-RDM résolu en spin sont exposés. Le modèle respecte la N-représentabilité et est adapté pour plusieurs données expérimentales (telles que XRD, PND, CS, MCS ou XMD). Le potentiel de ce modèle n'est pas limité à une analyse en spin mais son usage est ici circonscrit à la description des électrons non appariés, ses limites sont identifiées et des voies d'amélioration future sont proposéesHigh resolution X-ray diffraction (XRD) and polarized neutron diffraction (PND) are commonly used to model charge and spin densities in position space. Additionally, Compton scattering (CS) and magnetic Compton scattering (MCS) are the main techniques to observe the most diffuse electrons and unpaired electrons by providing the “Directional Compton Profiles" (DCPs) and ”Directional magnetic Compton Profiles" (DMCPs), respectively. A set of such DCPs (DMCPs) can be used to reconstruct two-dimensional or three-dimensional electron momentum density. Since all these techniques describe the same electrons in different space representations, we concentrate on associating the electron momentum density reconstructed from DCPs (resp. DMCPs) with electron density refined using XRD (resp. PND) data.The confrontation between theory and experiment, or between different experiments, providing several sets of experimental data, is generally obtained from the reconstructed electron densities and compared with theoretical results in position and momentum spaces. The challenge of comparing the results obtained by ab-initio computations and experimental approaches (in the Nit(SMe)Ph case) shows the necessity of a multiple experiments joint refinement and also the improvement of theoretical computation models. It proves that, in the case of a spin resolved electron density, a mere Hartree-Fock or DFT approach is not sufficient. In the YTiO3 case, a joint analysis of position and momentum spaces (PND & MCS) highlights the possible ferromagnetic pathway along Ti--O1--Ti. Therefore, a “super-position" spin density is proposed and proves to allow cross-checking the coherence between experimental electron densities in posittion and momentum spaces, without having recourse to ab initio results. Furthermore, an ”isolated Ti model" based on PND refined orbital coefficients emphasizes the importance of metal-oxygen coherent coupling to properly account for observations in momentum space.A one-electron reduced density matrix (1-RDM) approach is proposed as a fundamental basis for systematically combining position and momentum spaces. To reconstruct 1-RDM from a periodic ab initio computation, an "iterative cluster" approach is proposed. On this basis, it becomes possible to obtain a theoretical spin resolved 1-RDM along specific chemical bonding paths. It allows a clarification of the difference between Ti--O1--Ti and Ti--O2--Ti spin couplings in YTiO3. It shows that interaction contributions between atoms (metal and oxygen atoms) are different depending on whether the property is represented in position or momentum spaces. This is clearly observed in metal-oxygen chemical bonds and can be illustrated by an orbital resolved contribution analysis. Quantities for electron descriptions in phase space, such as the Moyal function, can also be determinerd by this "cluster model", which might be of particular interest if Compton scattering in Bragg positions could be generalized. The preliminary results of a simple spin resolved 1-RDM refinement model are exposed. The model respects the N-representability and is adapted for various experimental data (e.g.: XRD, PND, CS, MCS, XMD etc.). The potential of this model is not limited to a spin analysis but its use is limited here to the unpaired electrons description. The limitations of this model are analysed and possible improvements in the future are also proposed
35
Liang, Dong. "Semiconductor Nanowires: Synthesis and Quantum Transport." Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1327641946.
Повний текст джерела
36
Giacomoni, Laurence. "De la magnétorésistance géante à la magnétorésistance tunnel de multicouches magnétiques métalliques et métal/isolant." Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10156.
Повний текст джерелаАнотація:
Les etudes presentees dans ce memoire concernent le transport d'electrons polarises en spin dans les multicouches magnetiques et les effets qui en decoulent : la magnetoresistance geante dans les systemes metalliques et la magnetoresistance tunnel dans les systemes metal/oxyde. La magnetoresistance geante de multicouches nife/cu est etudiee dans les deux geometries de courant (planaire et perpendiculaire aux interfaces). Dans ces systemes, l'insertion de fines couches de co aux interfaces a pour effet de modifier le couplage indirect entre couches magnetiques successives et entraine une augmentation de l'amplitude de magnetoresistance. Parallelement, une etude de la variation angulaire de la resistance perpendiculaire a ete menee dans des vannes de spin a base de femn. Elle permet de confirmer le role predominant des electrons de caractere s et du mecanisme de diffusion dependante du spin dans le phenomene de magnetoresistance geante. L'effet tunnel d'electrons polarises en spin a ete etudie a la fois experimentalement et theoriquement. Les premiers resultats de caracterisations structurale, magnetique et de transport de multicouches discontinues (co/zro#2)#n sont presentes en fonction de l'epaisseur des couches magnetiques et des traitements thermiques. D'un point de vue theorique, nous avons etudie la magnetoresistance de jonctions magnetiques planaires de la forme mom' (m, m'=metaux ferromagnetiques, o=barriere d'oxyde) : introduction de couches antireflet selectives en spin aux interfaces et influence des epaisseurs des electrodes magnetiques.
37
Himbert, Marc. "L'helium-trois polarise gazeux en-dessous d'un kelvin : orientation par pompage optique, relaxation sur une paroi recouverte d'helium-quatre." Paris 6, 1987. http://www.theses.fr/1987PA066010.
Повний текст джерелаАнотація:
Orientation des spins nucleaires de **(3)he par pompage optique suivant la methode de colegrove et al. Et etude de la relaxation de ce systeme hors d'equilibre en champ magnetique faible du fait de l'adsorption sur les parois contenant des impuretes magnetiques. Etude detaillee de l'effet d'un film liquide de **(4)he a l'echantillon pour exclure **(3)he au voisinage des parois. Variation du temps de relaxation avec l'epaisseur du film, la composition de l'enduit, la densite gazeuse et la temperature, en tenant compte de la condensation de **(4)he quand on abaisse la temperature de l'adsorption de **(3)he sur le film, de sa dissolution a l'interieur et, en particulier, dans les premieres couches. Par rmn, observations de la precession libre des spins dans un champ magnetique inhomogene, et premieres determinations des coefficients de diffusion de spin dans **(3)he gazeux entre 1 et 0,5k. Obtention d'un taux d'orientation de quelques % vus 0,5k, avec un temps de relaxation de l'orientation longitudinale de 20 mn
38
Karraï, Khaled. "Etude de propriétés magnéto-optiques des hétérostructures de semiconducteurs III-V par spectroscopie submillimétrique." Grenoble 1, 1987. http://www.theses.fr/1987GRE10127.
Повний текст джерелаАнотація:
Interpretation des resultats experimentaux par un modele de transmission optique en presence de champ magnetique externe, developpe dans le formalisme de la fonction reponse; mise en evidence de l'absence d'interaction electron-phonon to etrange et d'une interpretation satisfaisante sans recours a l'interaction electron-phonon lo, indiquant l'importance de l'effet ecran dans la theorie de l'effet polaron resonnant. Etude de l'interaction spin-orbite induite par le champ electrique existant a l'interface; calcul des regles de selection des transitions entre niveaux de landau dans les differentes configurations magnetooptiques, differences par rapport aux semiconducteurs massifs
39
Mallardeau, Catherine. "L'hydrogène atomique polarisé : interaction avec les films d'Helium : expérience de compression." Paris 6, 1986. http://www.theses.fr/1986PA066186.
Повний текст джерелаАнотація:
Etude expérimentale de certains mécanismes de recombinaison de H| afin de comprendre les limites à l'obtention de la condensation de Bose Einstein. Mesure de l'énergie d'adsorption de H sur une couche mince 4He en fonction de l'épaisseur de la couche, paramètre qui donne les limites de stabilisation de H à basse température; obtention de la stabilisation sur des couches biomoléculaires. Construction d'un dispositif expérimental pour comprimer le gaz H| en champ magnétique de 20t, pour étudier le taux de recombinaison à 3 corps de H à haute densité et en champ magnétique intense.
40
Forano, Claude. "Les conducteurs protoniques : HSbO3.nH2O ET SnO2.nH2O : caracterisation, etude rmn et applications." Clermont-Ferrand 2, 1987. http://www.theses.fr/1987CLF21069.
Повний текст джерелаАнотація:
Preparation par une methode sol-gel permettant d'obtenir des materiaux de grande purete; mise en evidence de differences structurales importantes, d'une tres grande homogeneite morphologique et d'une difference importante de la taille des cristallites. Confirmation par rmn de l'existence de plusieurs especes protonees. Etude des variations de la conductivite en fonction de la temperature; influence de la teneur en eau. Mise en evidence de la relation entre la conductivite electrique et la mobilite protonique a partir de mesures des temps de relaxation et proposition d'un mecanisme de type grotthus. Elaboration de couches epaisses par serigraphie; possibilites d'application dans des dispositifs microioniques. Essais d'utilisation pour la detection de h::(2)
41
Celalettin, Metin. "‘A quantum observation technique; Quantum decoherence-by-depolarisation-tunnelling in a Spin Polarized Electron Gas, described by ‘Celalettin’s 1st Paradigm’’." Thesis, 2021. https://vuir.vu.edu.au/43943/.
Повний текст джерелаАнотація:
A Spin Polarized Electron Gas (SPEG) will be mathematically modelled to provide a medium in which the phenomenon will occur. Drawing on similar models consistent with the Quantum Monte Carlo (QMC) method, it will result in an equation enabling the medium to leave evidence of a foreign particle attempting to tunnel through it. This meets the objective of this study, quantum measurement. The SPEG’s spin exchange energy boundaries and collective electric dipole spin frequencies will enable the required Free Electron Laser (FEL) to be calibrated to the SPEG frequency forming the crux of the proposal. The mathematical model will leverage off investigations that have been performed at the single electron level, such as precession manipulation and application to a SPEG. This research will then present a formula that describes a SPEG pierced by a FEL and producing a resultant tunnel; its walls stoned by spin-flipped electrons. The formula presented will be the energy expression of the tunnel by depolarization.
42
Chen, Li-Jie, and 陳俐潔. "Spin Polarized Electron Beam Emission From Graphene Probes." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/r75nsc.
Повний текст джерелаАнотація:
碩士國立臺灣海洋大學
光電科學研究所
106
Graphene has many special electronic properties, different to the metal conductor, not only has highest carrier mobility but also has the ability to maintain the electron spin properties in a long range at room temperature. This thesis describes a method of graphene growth on copper by chemical vapor deposition, follow by the mechanical cutting to generate a home-made graphene edge emitter electron source. This electron source was then place into an electron beam measurement system which has three-electrode structure. It contains a thermal adjustable cathode, a pinhole anode and a fluorescent screen. The graphene edge field emission and measure of thermal-field emission characteristics are observed from this system. Our experiment focus on the injection of spin-polarized electron into graphene edge when the magnetic field was applied on ferromagnetic electrode that attached on the graphene probe. Another magnet on the screen electrodes are placed an the magnetic field dependence of field emission current is observed. We are able to measure the electron beam spin-polarization degree from such innovated electron source. Finally, the spin polarization was calculated as 49% by the measurement. Also, we final the electron beam brightness is 4.22×10^10 Am^(-2) sr^(-1) V^(-1)。
43
Mulhollan, Gregory Anthony. "Surface studies using spin-polarized electron energy loss spectroscopy." Thesis, 1990. http://hdl.handle.net/1911/16376.
Повний текст джерелаАнотація:
Spin-polarized electron energy loss spectroscopy (SPEELS) has been used to investigate several paramagnetic surfaces. In this technique, a low energy beam of spin-polarized electrons from a GaAs source is directed at the surface to be studied and the spin-polarization of the emitted electrons, as well as the kinetic energy distribution, is measured via a micro-Mott polarimeter equipped with a retarding potential energy analyzer. The near-elastic-energy electrons contain information on the inelastic scattering channels available in the solid. The spin-polarization of these same electrons is sensitive to the shape of the final state manifold, i.e., the density of unoccupied states. The low energy and behavior of the spin-polarization spectrum mainly reflects the high number of unpolarized electrons present near zero kinetic energy. Results from Cu(100), polycrystalline Au, GaAs(110), GaAs(100) and Mo(110) surfaces suggest that exchange scattering with spin-flip is ubiquitous for the lowest energy electron beam energies studied ($\sim$14 eV). A simple convolution of the empty and occupied densities of states correctly predicts the shape of the energy dependent spin-flip rate.
44
O'Gorman, Brian Curtin. "Spin-polarized transport in magnetic nanostructures." Thesis, 2009. http://hdl.handle.net/2152/ETD-UT-2009-12-550.
Повний текст джерелаАнотація:
Two of the principal phenomena observed and exploited in the field of spintronics are giant magnetoresistance (GMR) and spin transfer torque (STT). With GMR, the resistance of a magnetic multilayer is affected by the relative orientation of its magnetic layers due to (electron) spin dependent scattering. For the STT effect, a spin-polarized electric current is used to alter the magnetic state of a ferromagnet. Together, GMR and STT are at the foundation of numerous technologies, and they hold promise for many more applications. To achieve the high current densities (~10¹² A/m²) that are necessary to observe STT effects, point contacts – constricted electrical pathways (~1–100 nm in diameter) between conducting materials – are often used because of their small cross-sectional areas. In this sense, we have explored STT in bilayer magnetic nanopillars, where an electric current was used to induce precession of a ferromagnetic layer. This precessional state was detected as an increase in resistance of the device, akin to GMR. Temperature dependent measurements of the onset of precession shed light on the activation mechanism, but raised further questions about its detailed theory. Point contacts can also be used as local sources or detectors of electrons. In this context, we have observed transverse electron focusing (TEF) in a single crystal of bismuth. TEF is a k-selective technique for studying electron scattering from within materials. Using lithographically fabricated point contacts, we have studied the temperature dependence of the relaxation time for ballistic electrons from 4.2 to 100 K. These measurements indicated a transition between electron-electron dominated scattering at low temperatures and electron-phonon scattering as the Debye temperature was approached. We present preliminary work toward a TEF experiment to measure spin dependent scattering from a non-magnet/magnet interface. We also investigated spin wave propagation in thin, magnetic waveguide structures. At the boundary between the waveguide and continuous magnetic film, spin wave rays were found to radiate into the film, or to reflect and form standing waves in the waveguide. A circular defect in the waveguide was observed to cause diffraction of spin waves, generating an interference pattern of higher modes of oscillation.text
45
Huang, Tsai-Yu, and 黃才育. "Spin-dependent transport in a two-dimensional GaAs electron gas." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/80263806589834298892.
Повний текст джерелаАнотація:
碩士國立臺灣大學
物理學研究所
89
1. Spin-dependent transport in a perpendicular magnetic field: We have measured the low-temperature electron transport properties in a front-gated GaAs/Al0.3Ga0.7As heterostructure. Collapse of spin-splitting and an enhanced Lande |g|-factor at Landau level filling factors both n = 3 and n = 1 are observed. Our experimental results show direct evidence that the electron-electron interactions are stronger at n = 3 than those at n = 1; and the effective disorder is stronger at n = 1 than that at n = 3 over approximately the same perpendicular magnetic field range 4 T≦B≦6 T. 2. Spin-dependent transport in a parallel magnetic field: Applying an in-plane magnetic field parallel B|| to a two-dimensional electron gas is a powerful tool to study spin-dependent electron transport since a B|| only couples to the electron’s spin. We observe an enhancement of magnetoresistance of a two-dimensional electron system with increasing parallel magnetic field. Using a simple model, we suggest that the increase of magnetoresistance is due to spin but the model over-estimates the Lange |g |-factor in our system.
46
MULHOLLAN, GREGORY ANTHONY. "A SPIN-POLARIZED LOW-ENERGY ELECTRON DIFFRACTION STUDY OF A MAGNETIZED NICKEL(111) SURFACE." Thesis, 1987. http://hdl.handle.net/1911/13244.
Повний текст джерелаАнотація:
Spin-polarized low energy electrons from a GaAs source were used to probe magnetized nickel(111) surface. Intensity curves as well as spin-orbit and exchange induced polarization asymmetries were obtained for the $(00)-20\sp\circ, (00)-30\sp\circ,$ $(00)-45\sp\circ, (10)$ and $(-10)$ beams. Comparison with a preliminary theoretical study yields no quantitative information on the magnetic moment per surface atom.
47
Lancaster, James Campbell. "A low-energy, electron-spin-polarized helium(+) ion source for use in surface studies." Thesis, 1998. http://hdl.handle.net/1911/17237.
Повний текст джерелаАнотація:
A spin polarized He$\sp+$ ion source has been developed to study the dynamics of ion-surface interactions. The He$\sp+$ ions are produced by Penning ionization in collisions between electron-spin-polarized He(2$\sp3$S) metastable atoms contained in a weak rf-excited discharge. The ions are extracted from the discharge and focused onto clean or adsorbate-covered surfaces using a series of electrostatic lenses. The impact energy can be varied from $\rm{<}10eV$ to $\rm{\ge}650eV$ and typical beam polarizations are 10-15%. Information about ion/surface interactions, and the dependence of those interactions on the incident ion energy, is obtained by measuring the energy distribution and polarization of electrons ejected from the surface as a result of Auger neutralization.
48
Maseberg, Jack William. "Fluorescence polarization of atomic, dissociated atomic, and molecular transitions induced by spin-polarized electron impact." 2009. http://proquest.umi.com/pqdweb?did=1834801371&sid=13&Fmt=2&clientId=14215&RQT=309&VName=PQD.
Повний текст джерелаАнотація:
Thesis (Ph.D.)--University of Nebraska-Lincoln, 2009.Title from title screen (site viewed July 6, 2010). PDF text: x, 133 p. : ill. (some col.) ; 3 Mb. UMI publication number: AAT 3366064 . Includes bibliographical references. Also available in microfilm and microfiche formats.
49
Pradeep, A. V. "Development of a Spin-Polarized Low Energy Electron Diffraction System and Investigation on Spin-Orbit and Exchange Interactions on Ir(100) and Ultrathin Fe(100) Grown on Ir(100)." Thesis, 2016. http://hdl.handle.net/2005/3202.
Повний текст джерелаАнотація:
Spin-polarized electron beam has not yet been produced from an unpolarized electron beam using Stern-Gerlach type spin filter, because of the Lorentz force and Heisenberg uncertainty principle. At present, electron spin detectors and filters work on the basis of spin-dependent scattering of an electron beam from crystal surfaces. Single channel efficiencies of all the spin detectors for electrons are orders of magnitudes lower than the ideal one. Specular reflection type spin-polarized low energy electron diffraction (SPLEED)-spin detectors are having higher single channel efficiencies compared to the conventional Mott detectors. Moreover, multichannel detection can be realized from specular reflection type SPLEED-spin detectors. They have higher effective efficiency than the ideal spin detector. In order to develop specular reflection type spin filter, it is important to develop a spin-polarized low energy electron diffraction system. In addition, SPLEED system allows us to study the spin-orbit and exchange scattering at crystal surfaces.
The general direction of the thesis has been the development of spin-polarized low energy electron diffraction (SPLEED) system. This system has been used to investigate the spin-orbit interactions on Ir(100) surface and exchange interactions of Fe grown on Ir(100). The thesis is organized into chapters as follows.
Chapter 1 introduce the reader to some of the basic concepts of polarized electrons and the evolution of spin-polarized electron sources and detectors. Sources of polarized electrons are discussed with emphasis on photocathodes such as GaAs and strained GaAs. Widely used spin detector is the Mott detector which works in the higher energy range. The working principle of the Mott detector is discussed. Commonly used spin detector in the lower energy range is the LEED detector. The concept of the LEED detector is also discussed. Working principle and recent developments of specular reflection type SPLEED spin filters are introduced. Evolution of electron spin detector is discussed towards the end of the chapter.
Chapter 2 discusses about the two instruments designed and developed during the course of the thesis. The first one is a spin-polarized low energy electron diffraction system working in the reflected electron pulse counting mode in UHV. This system is capable of measuring spin asymmetries due to spin-orbit interaction and exchange interaction. This instrument is useful in understanding structure and magnetism at surfaces as well as helps to develop new spin polarimeter based on SPLEED by evaluating spin asymmetries from different surfaces. All instruments connected to SPLEED system, measurement protocol and controlling software are discussed with some details. Along with this, standard characterization tools such as X-ray diffraction and magneto-optic Kerr effect measurements are discussed. The second instrument is a novel quadratic magneto-optic Kerr effect measurement system using permanent magnets, which is simple, compact and cost-effective. We have used rotating field method to extract QMOKE component in saturation. So there is no need for precise real-time measurement of magnitude and direction of the magnetic field as in the case of vector magnet. This instrument can easily quantify QMOKE coefficients for ferrimagnetic and ferromagnetic thin films and single crystals.
Chapter 3 discusses SPLEED experiments carried out on Ir(100)-(1×5)-Hex and Ir(100)-(1×2+2×1)-O surfaces. The surface structure and surface preparation techniques are discussed. The stability of the Ir(100)-(1×5)-Hex surface is evaluated by monitoring the spin asymmetry as the function of time. Within 25 hours after the surface preparation, the profile of the spin asymmetry and the reflected electron count for Ir(100)-(1×5)-Hex surface resembles that of hydrogen adsorbed Ir(100)-(1×5)-H surface. The electron energy-angle of incidence landscape of reflectivity, spin asymmetry and figure of merit are recorded for Ir(100)-(1×2+2×1)-O surface. Many wide regions with a large figure of merit are identified in the E- landscape.
Chapter 4 reports SPLEED experiments carried out on Ir(100)-(1×5)-H surface. The comparison between asymmetries evaluated for the Ir(100)-(1×5)-Hex surface after 25 hours and Ir(100)-(1×5)-H surface suggests that Ir(100)-(1×5)-Hex surface is transforming to Ir(100)-(1×5)-H surface, in 25 hours. This can be due to the adsorption of more than four Langmuir of residual hydrogen during this time. The energy-angle landscape of reflectivity, asymmetry and figure of merit are recorded for Ir(100)-(1×5)-H surface in an energy range 20 eV to 100 eV and angle range 10 to 60 . Many regions are identified as the working point for specular reflection type spin filter based on SPLEED. The surface structure and surface preparation techniques are discussed. The stability of the surface is also evaluated.
Chapter 5 investigates the growth and magnetic properties of Fe(100) film on Ir(100)-(1×1), Ir(100)-(1×5)-Hex and Ir(100)-(1×2+2×1)-O surfaces. LEED, MEED, LMOKE and QMOKE studies were presented. The growth is found to be layer-by-layer at least up to 20 monolayers (ML) at room temperature. At higher deposition temperature, the MEED oscillations disappear around 3-5 ML. Magnetic anisotropy of the Fe(100) film grown on Ir(100)-(1×2+2×1)-O surfaces is evaluated using LMOKE measurement using Kerr microscope. Simultaneous in-situ LMOKE and MEED measurements were carried out during the deposition. Ferromagnetic ordering with an in-plane easy axis starts above 4.5 ML at room temperature. The Kerr rotation normalized by thickness is evaluated in the pseudomorphic regime and strain relaxed regime. The probing depth of the MOKE is found to be around 14 nm in Fe(100)/Ir(100). An antisymmetric component is observed in the re-magnetization loop measured using MOKE. This antisymmetric loop arises due to the quadratic magneto-optic coupling which is separated by symmetrization and antisymmetrization procedure. The observed quadratic magneto-optic coupling suggests that the analysis based on the assumption that the magneto-optic coupling is linear in magnetization has to be modified. In order to quantify the quadratic magneto-optic coupling parameters, a QMOKE measurement system is developed and measurements were carried out.
Chapter 6 discusses SPLEED experiments carried out on various thicknesses of Fe(100) film. Fe(100) films grown on Ir(100) substrate with the thickness less than or equal to 4 ML is not ferromagnetic with in-plane easy axis at room temperature. The non-zero exchange asymmetry observed for 5 ML and above indicates the presence of ferromagnetic ordering. A difference in the profile of exchange asymmetry is observed between pseudomorphic and strain relaxed regime. Large spin-orbit asymmetry is observed for 1 ML and 2 ML Fe(100) which is unexpected from a low atomic number (Z) material. The reason for large spin-orbit asymmetry is still unknown. The energy-angle landscape of reflectivity, exchange asymmetry, spin-orbit asymmetry and figure of merit were evaluated for 21 ML of Fe(100). Many working points were identified for different types multichannel spin filter based on exchange interaction
Finally, the various results are summarized and a broad outlook is given.
50
Lancaster, James Campbell. "Investigating the dynamics of ion-surface interactions using electron-spin-polarized positively charged helium ions." Thesis, 2002. http://hdl.handle.net/1911/18101.
Повний текст джерелаАнотація:
Spin-labeling techniques, specifically using electron-spin-polarized 4He+ ions coupled with energy-resolved measurements of the polarization of ejected electrons, are providing significant insight into surface electronic states and the dynamics of the neutralization of charged particles at clean and adsorbate-covered metal surfaces. The electronic structure of surfaces and the process by which charged particles electrically interact with such surfaces are of fundamental interest, yet only partially understood. A powerful technique for studying surface states and interactions has been Ion Neutralization Spectroscopy, in which noble gas ions are directed into a surface, where they are neutralized by electrons from the surface. Energy conservation causes other electrons to be emitted, which are collected and their energy distributions analyzed. Because neutralization takes place outside the surface, this technique serves as a sensitive probe of that part of the material. The current studies expand this technique by analyzing spin-aspects of the interaction. Spin-polarized He+ ions are produced in a radio-frequency driven discharge and directed at selected surfaces. Emitted electrons are analyzed with a retarding grid energy analyzer to determine their energy distributions and a mott polarimeter to measure their spin polarization. Correlating the spins of the outgoing electrons and incoming ions provides previously unavailable information about the dynamics of this reaction. Analysis of the energy distributions and polarization of electrons emitted from Au(100), Cu(100), and Al(100) indicate that neutralization occurs at distances closer to the surface than previously believed, and that for the period during which the ion is close to the surface, its presence causes a spin-dependent perturbation in the local density of electronic states---in essence, it locally magnetizes the surface. Further, the data indicate that surface plasmon excitation, a prominent feature in several theoretical models, does not appear to play a significant role in ion neutralization. Polarization data collected on alkali-covered surfaces clarify the dynamics by which the neutralization process takes place, while CO2 surface studies reveal that the ions undergo a previously unexamined neutralization mechanism which should apply to a broad range of van der Waals solids.