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Dissertations / Theses on the topic 'Organic superconductors'
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1
Qayyum, M. M. B. "Organic electronic materials : electroreticulated conductive polymers and potential organic superconductors." Thesis, London South Bank University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.618648.
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Clayton, N. J. "Quantum oscillations in organic metals and superconductors." Thesis, University of Bristol, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326720.
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Marsden, Ian Richard. "Low dimensional organic conductors." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239593.
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McDonald, Ross David. "Optical studies of crystalline organic superconductors under extreme conditions." Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393379.
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Obertelli, S. D. "Magnetic properties of low-dimensional solids." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305925.
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Malone, Liam Douglas. "The gap symmetry of the organic and iron based pnictide superconductors." Thesis, University of Bristol, 2009. http://hdl.handle.net/1983/ec8fb6fa-505b-42c4-b8ea-c128575336b3.
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Kornelsen, Kevin E. "Infrared optical properties of the organic superconductor (BEDT-TTF)₂[Cu(NCS)₂] and the search for the superconducting gap." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/30848.
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The optical properties of the 10.4 K organic superconductor, κ-{BEDT—TTF)₂[CU-(NCS)₂], are the subject of this thesis. This organic superconductor is a crystalline solid consisting of planes of BEDT-TTF molecules separated by planes of Cu{NCS)₂ anions. The arrangement of molecules results in electrical two-dimensionality, with high conductivity within the planes of BEDT-TTF molecules and poor conductivity in the perpendicular direction. Until the recent discovery of an organic superconductor with TC = 11.5 K, the 10.4 K transition of (BEDT-TTF)₂[Cu(NCS)₂] was the highest in the class of organic metals.
Optical properties of superconductors have played an important role in analysis of their unusual properties. Using single crystals of (BEDT—TTF)₂[Cu(NCS)₂] and light polarized within the highly conducting plane, I have measured both specular reflectivity and bolometric absorption over a wide region of the infrared spectrum. The reflectivity measurements cover most of the far and mid-infrared for both protonated and deuter-ated compounds, with sample temperatures between 300 K and 6.5 K. The resulting spectra show contributions from electronic interband transitions, intraband transitions, and molecular phonon vibrations.
A search for the superconducting energy gap was undertaken using the bolometric technique to measure the sample absorption at far-infrared energies. These measurements were performed at temperatures below Tc and cover the part of the spectrum where condensation of electrons into superconducting Cooper pairs should be directly observable optically. On other materials, measurements in this part of the spectrum have directly revealed the binding energy for the superconducting electron pairs, and have been instrumental in showing that details of the electron-phonon interactions are very important in superconducting systems. In the spectra which we have measured, any effect of the superconducting transition is overwhelmed by other contributions to the absorption in the far-infrared energy region.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Shimojo, Yoshiro. "Upper Critical Field of Low-Dimensional Organic Superconductors under Parallel Magnetic Fields." 京都大学 (Kyoto University), 2002. http://hdl.handle.net/2433/149957.
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Vaccarella, Cawley D. "A theoretical analysis of the spin susceptibility tensor and quasiparticle density of states for quasi-one-dimensional superconductors." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/27670.
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Al-Hossain, Md Shahriar. "Study of superconducting and electromagnetic properties of un-doped and organic compound doped MgB₂ conductors." Access electronically, 2008. http://ro.uow.edu.au/theses/90.
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Guterding, Daniel [Verfasser], Roser [Akademischer Betreuer] [Gutachter] Valenti, Igor I. [Gutachter] Mazin, and Rafael [Gutachter] Fernandes. "Microscopic modelling of organic and iron-based superconductors / Daniel Guterding ; Gutachter: Roser Valenti, Igor I. Mazin, Rafael Fernandes ; Betreuer: Roser Valenti." Frankfurt am Main : Universitätsbibliothek Johann Christian Senckenberg, 2017. http://d-nb.info/1134952279/34.
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Taylor, Owen. "Specific heat studies of the organic superconductors k-(BEDT-TTF)2Cu[N(CN)2]Br and k-(BEDT-TTF)2Cu(NCS)2." Thesis, University of Bristol, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492467.
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The measurement of specific heat provides unique information concerning the superconducting state. It has the advantage over many other techniques as in that it is a bulk thermodynamic probe and as such is relatively insensitive to the presence of minority impurity phases. For this thesis, two calorimeters were designed, built and calibrated to measure ae specific heat of various exotic superconductors in the form of sub-milligram single crystals.
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Hardikar, Rahul Padmakar. "Dynamic electron-phonon interactions in one-dimensional models." Diss., Mississippi State : Mississippi State University, 2007. http://library.msstate.edu/etd/show.asp?etd=etd-11092007-143010.
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Roth, Friedrich. "Electronic structure of selected aromatic hydrocarbon systems investigated with electron energy-loss spectroscopy." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-106800.
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Organic materials with fascinating/intriguing electronic properties have been the driving force for many research activities in the past, and in particular for important progress in materials science covering both new functional materials as well as theoretical developments. In addition, charge transfer, i. e., the addition or removal of charges to or from molecules in organic solids is one route to modify and control their electronic properties. Recently, the discovery of superconductivity in several alkali metal intercalated hydrocarbon systems (picene, phenanthrene, coronene and 1,2;8,9-dibenzopentacene) with rather high transition temperatures has opened a new chapter in organic material science as well as solid-state physics.
The search for a microscopic understanding of the mechanism that drives materials superconducting always has initiated a large number of scientific activities, and there are numerous examples where these activities have provided major advancement. A basic foundation of this understanding is the knowledge of the electronic properties of the material under investigation.
In this context, this thesis reports first, very detailed insight into the electronic structure of both undoped as well as potassium doped picene, coronene and 1,2;8,9-dibenzopentacene using electron energy-loss spectroscopy (EELS) as main experimental method. Additionally, also photoemission spectroscopy experiments have been performed to investigate the occupied electronic density of states close to the chemical potential. In order to learn more about the electronic structure we have compared the results we obtained from EELS and photoemission spectroscopy with theoretical calculations based on Density functional theory (DFT) using the local-density approximation (LDA).
We identify the peculiar case of very close lying conduction bands that upon doping harbour the electrons that form the Cooper-pairs in the superconducting state. Moreover, the presented data display substantial changes in the electronic excitation spectrum upon doping, whereas in the doped case the appearance of one new peak (for picene) and several new peaks (for coronene and 1,2;8,9-dibenzopentacene) in the former optical gap is reported. By using a Kramers–Kronig analysis (KKA) it is possible to gain information about the nature of this doping introduced excitations. In particular, in case of picene, the new low energy feature can be assigned to a charge carrier plasmon. Interestingly, this plasmon disperses negatively upon increasing momentum transfer, which deviates significantly from the traditional picture of metals based on the homogeneous electron gas. The comparison with calculations of the loss function of potassium intercalated picene shows how this finding is the result of the competition between metallicity and electronic localization on the molecular units.
Furthermore, core level excitation measurements show the reduction of the lowest lying C 1s excitation feature, which clearly demonstrates that potassium intercalation leads to a filling of the conduction bands with electrons. Additionally, the measurements of potassium intercalated 1,2;8,9-dibenzopentacene clearly indicate the formation of particular doped phases with compositions K_xdibenzopentacene (x = 1, 2, 3), whereas the data suggest that K_1dibenzopentacene has an insulating ground state with an energy gap of about 0.9 eV, while K_2dibenzopentacene and K_3dibenzopentacene might well be metallic, because of the absent of an energy gap in the electronic excitation spectra.
Interestingly, a comparison of the photoemission as well as EELS spectra of undoped 1,2;8,9-dibenzopentacene and pentacene reveal that the electronic states close to the Fermi level and the electronic excitation spectra of the two materials are extremely similar, which is due to the fact, that the additional two benzene rings in 1,2;8,9-dibenzopentacene virtually do not contribute to the delocalized pi molecular orbitals close to the Fermi level. This close electronic similarity is in contrast to the behavior upon potassium doping, where evidence for a Mott state has been reported in the case of pentacene.
A comparison of the low energy excitation spectra of chrysene with picene (phenacenes) as well as tetracene with pentacene (acenes) crystals reveal a significant difference between the former and the latter two materials. While for the phenacenes (zigzag arrangement) the excitation onset is characterized by up to five weak excitation features with only small anisotropy and without visible Davydov splitting within the a*, b*-planes, the acene (linear arrangement) spectra are dominated by a large excitation close to the onset and a sizable Davydov splitting. The presented data show further that the spectral shape of the pentacene excitation spectrum provides clear evidence for a large admixture of molecular Frenkel-type excitons with charge-transfer excitations resulting in excited states with a significantly mixed character. This conclusion is in good agreement with recent advanced calculations which predicted a charge-transfer admixture to the lowest singlet excitation which is significantly dependent upon the length of the acene molecules. Moreover, also for picene and chrysene we observe differences which point towards an increased charge-transfer contribution to the singlet excitation spectrum in the former.
Finally, investigations of the electronic properties of undoped and potassium doped chrysene, a close relative of picene, show that the doping introduced changes are in a similar range such as observed in case of picene. Interestingly, due to the analogy between the observed changes in the electronic structure upon potassium doping between chrysene and picene and further similarity in the crystal structure we speculate that chrysene is a promising candidate for another aromatic hydrocabon superconductor.
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Watanabe, T., H. Yokoyama, Y. Tanaka, and J. Inoue. "Predominant magnetic states in the Hubbard model on anisotropic triangular lattices." American Physical Society, 2008. http://hdl.handle.net/2237/11256.
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Graham, Anthony William. "Synthesis and properties of charge transfer salts of BEDT-TTF." Thesis, University College London (University of London), 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336241.
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Analytis, James. "Confinement and coherence : finite-sized models and disorder experiments on an organic superconductor." Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427904.
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Wang, Wei. "Computational and synthetic approaches to the synthesis of a potential high-temperature organic superconductor precursor: C₃₆ N₄." [Bloomington, Ind.] : Indiana University, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3337538.
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Thesis (Ph.D.)--Indiana University, Dept. of Chemistry, 2008.Title from PDF t.p. (viewed on Jul 27, 2009). Source: Dissertation Abstracts International, Volume: 69-11, Section: B, page: 6813. Adviser: Lawrence K. Montgomery.
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Dhakal, Pashupati. "Angular Magnetoresistance Oscillations in the Molecular Organic Conductor (DMET)2I3: Experiment and Calculation." Thesis, Boston College, 2010. http://hdl.handle.net/2345/1566.
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Thesis advisor: Michael J. NaughtonQuasi-one dimensional (Q1D) molecular organic conductors are among the most exciting materials in condensed matter physics, exhibiting nearly every known ground state. They are highly anisotropic, structurally and electronically, and show large oscillatory phenomena in conductivity for magnetic field rotated in different crystalline planes. Several theoretical works have been published to explain these angular magnetoresistance oscillation (AMRO) effects, but the underlying physics remains illunderstood. Here, we present measurements and calculations of magnetotransport in the molecular organic (super)conductor (DMET)2I3 which detect and simulate all known AMRO phenomena for Q1D systems. Employing, for the first time, the true triclinic crystal structure in the calculations, these results address the mystery of the putative vanishing of the primary AMRO phenomenon, the Lebed magic angle effect, for orientations in which it is expected to be strongest. They also show a common origin for Lebed and so-called "Lee-Naughton" oscillations, and confirm the generalized nature of AMRO in Q1D systems. Furthermore, we report the temperature dependence of the upper critical magnetic field in (DMET)2I3, for magnetic field applied along the intrachain, interchain, and interplane directions. The upper critical field exhibits orbital saturation at low temperature for field in all directions, implying that superconductivity in (DMET)2I3 is conventional spin singlet
Thesis (PhD) — Boston College, 2010
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
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Erbe, Manuela, Jens Hänisch, Thomas Freudenberg, Anke Kirchner, Stefan Kaskel, Ingolf Mönch, Ludwig Schultz, and Bernhard Holzapfel. "Improved REBa₂Cu₃O₇₋ₓ (RE ═ Y, Gd) structure and superconducting properties by addition of acetylacetone in TFA-MOD precursor solutions." Royal Society of Chemistry, 2014. https://tud.qucosa.de/id/qucosa%3A36162.
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For developing commercially utilized high-performance high-temperature superconductors, the fabrication of biaxially textured (RE)Ba₂Cu₃O₇₋ₓ (REBCO, RE ═ Y, Gd) coated conductors via metal–organic decomposition of trifluoroacetate precursors (TFA-MOD) has become an interesting strategy for industrial scale-up due to low costs and simple operation. However, the hygroscopic nature of commonly used precursor solutions makes them very sensitive to water pollution through air humidity. This can lead to a degradation of the final microstructure, which in return deteriorates critical current densities. Here, we present a new method to overcome that problem by using a moderator of 2,4-pentanedione (acac) in a pre-existing REBCO precursor solution. Our results show that even initially low-performance solutions can be enhanced to such an extent that they finally outperform standard high-performance solutions and the temperature window for their optimal growth widens significantly. Scanning electron microscopy gives evidence of considerable microstructural improvements, e.g. avoidance of pore formation and grooves, reduction of buckling and surface granularity. X-ray investigations indicate texture improvements, and electrical measurements reveal that transport critical current densities (Jc) increase in self-field and applied magnetic fields. For YBCO, a molar ratio of acac/RE ═ 0.64 is most effective and leads to an increase of the maximum pinning force density Fmaxp from 1.0 to 2.4 GN mˉ³ at 77 K. For GdBCO, a broad window of annealing temperatures (790–840°C) is possible for films with Jc values above 2.9 MA cmˉ² and Fmaxp above 3 GN mˉ³ at 77 K.
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Takigawa, M., M. Ichioka, K. Kuroki, Y. Asano, and Y. Tanaka. "Effect of the Vortices on the Nuclear Spin Relaxation Rate in the Unconventional Pairing States of the Organic Superconductor (TMTSF)2PF6." American Physical Society, 2006. http://hdl.handle.net/2237/8850.
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Brun, Sulyvan. "Etudes structurales des conducteurs organiques bidimensionnels à haute pression." Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENY034/document.
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Les conducteurs organiques à base du sel de transfert de charge bis(éthylènedithio)tétrathiafulvalène (BEDT-TTF ou ET) montrent un comportement électrique allant de semi-conducteur à métal supraconducteur. La pression peut induire des petits changements structuraux qui s'accompagnent de changements très important des propriétés physiques. L'étude de l'évolution de la structure de ces composés sous pression, dont les mailles sont de faible symétrie contenant plusieurs dizaines d'atomes légers, constitue un défi. Le but de ce travail est d'étudier ces changements structuraux induits par la pression en utilisant la diffraction des rayons X sur monocristaux. Les monocristaux de six conducteurs et supraconducteurs organiques (α-(BEDT-TTF)2I3, β-(BEDT-TTF)2I3, κ-(BEDT-TTF)2I3, α-(BEDT-TTF)2KHg(SCN)4, κ-(BEDT-TTF)2Cu(NCS)2, et κ-(BEDT-TTF)2Cu[N(CN)2]Br) ont été étudiés à haute pression (jusqu'à 32 GPa) dans une cellule à enclumes de diamant sur la ligne de lumière ID09A à l'ESRF. L'hélium a été utilisé comme milieu transmetteur de pression. Les compressibilités de ces six composés ainsi que leurs positions atomiques ont été déterminées sous pression. Pour la première fois, les transitions de phases structurales réversibles de α-(BEDT-TTF)2I3 vers αHP-(BEDT-TTF)2I3 à 13.6 GPa, et de κ-(BEDT-TTF)2Cu(NCS)2 vers κHP-(BEDT-TTF)2Cu(NCS)2 à 8.5 GPa ont été observées, et les structures originales à haute pression ont été décrites avec succès. Les changements structuraux observés ont été appuyés par des mesures RamanOrganic conductors based on charge-transfer salt of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) exhibit electronic properties ranging from semiconducting to metallic to superconducting. Pressure can induce subtle structural rearrangements associated with drastic changes in physical properties. Study of the pressure induced structural changes of these compounds, with low symmetry unit cells containing dozens of light atoms, is a challenge. The aim of this work is to investigate pressure-induced structural changes with single crystal X-ray diffraction. Single-crystals of six organic conductors and superconductors (α-(BEDT-TTF)2I3, β-(BEDT-TTF)2I3, κ-(BEDT-TTF)2I3, α-(BEDT-TTF)2KHg(SCN)4, κ-(BEDT-TTF)2Cu(NCS)2, and κ-(BEDT-TTF)2Cu[N(CN)2]Br) were studied at high-pressures (up to 32 GPa) in a diamond-anvil cell on the ID09A beamline at the ESRF. Helium was used as pressure transmitting-medium. The compressibilities of the six compounds are reported, and atomic positions were determined under pressure. For the first time, reversible structural phase transitions in α-(BEDT-TTF)2I3 to αHP-(BEDT-TTF)2I3 at 13.6 GPa, and in κ-(BEDT-TTF)2Cu(NCS)2 to κHP-(BEDT-TTF)2Cu(NCS)2 at 8.5 GPa have been observed, and the original high pressure structures have been described successfully. Raman measurements agree well with the observed structural changes
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Beyer, Rico. "Winkelaufgelöste Messungen der spezifischen Wärme des organischen Supraleiters beta''-(ET)2SF5CH2CF2SO3." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-105892.
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Im Jahr 1964 wurde eine Theorie der Supraleitung vorgestellt, welche Cooper-Paarbindungen mit nichtverschwindendem Gesamtimpuls berücksichtigt. Sie wird nach den maßgeblich beteiligten Physikern P. Fulde, R. A. Ferrell, A. I. Larkin und Y. N. Ovchinnikov als FFLO-Supraleitung bezeichnet [1, 2]. Aufgrund recht anspruchsvoller Voraussetzungen kommen nur wenige Festkörper-Systeme in Frage, die eine FFLO-Phase ausbilden könnten. Im Jahr 2007 konnte R. Lortz durch Messungen der spezifischen Wärme an dem organischen Supraleiter kappa-(ET)2Cu(NCS)2 einen soliden Nachweis für eine weitere thermodynamische Supraleitungs-Phase in hohen Magnetfeldern erbringen [3]. ET steht hierbei für Bis-(ethylen-dithiolo)-tetrathiafulvalen.
Die Hochfeld-Phase von kappa-(ET)2Cu(NCS)2 erfüllt alle bekannten Bedingungen für einen FFLO-Zustand. Diese Arbeit befasst sich mit der Erbringung eines gleichwertigen Beweises einer thermodynamischen Hochfeld-Supraleitungs-Phase in dem quasi-zweidimensionalen und vollständig organischen Supraleiter beta\'\'-(ET)2SF5CH2CF2SO3 durch hochauflösende Messungen der spezifischen Wärme. Darüber hinaus sollte durch eine präzise Ausrichtung der Probe zum Magnetfeldvektor die Feldorientierungsabhängigkeit der spezifischen Wärme und damit der supraleitenden Phasen bestimmt werden.
[1] - P. Fulde and R.A. Ferrell, Phys. Rev., 135:A550, (1964).
[2] - A.I. Larkin and Y.N. Ovchinnikov, Zh. Eksp. Teor. Fiz., 47:1136,(1964).
[3] - R. Lortz et al., Phys. Rev. Lett., 99:187002, (2007).
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Weiß, Herbert Dieter. "Fermi surface studies on the organic superconductor Kappa-(BEDT-TTF) 2 Cu[N[CN] 2 ]Br and on the alkanline earth subnitride NaBa 3 Nby means of magneto-quantum oscillations." [S.l. : s.n.], 2001. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB9218369.
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Fertey, Pierre. "Adaptation de la diffraction des rayons X par des poudres à l'étude des transitions de phases structurales entre 3K et 470K : application à l'étude des corrélations entre propriétés électroniques et structurales dans le composé organique (TMTSF)2ClO4." Université Joseph Fourier (Grenoble ; 1971-2015), 1995. http://www.theses.fr/1995GRE10196.
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La premiere partie est consacree a une revue des developpements de la technique experimentale de la diffraction des rayons x par des echantillons polycristallins (methode des poudres). Il est ici demontre que cette technique est aujourd'hui une methode pertinente pour l'analyse des proprietes structurales des materiaux. Dans une seconde partie, une application originale de la methode des poudres est presentee: un diffractometre de haute resolution fonctionnant entre 3 k et 470 k, a ete concu puis realise, pour l'analyse des contributions structurales dans les mecanismes regissant les transitions de phases (resolution des structures cristalline, mesure de la dilatation thermique, mise en evidence de transitions de phases/distorsions structurales). Les caracteristiques et les performances de ce diffractometre a temperature controlee sont exposees a travers plusieurs applications (transitions de phases avec deux parametres d'ordre correles, temperature de debye). La troisieme partie illustre une etude par diffraction des rayons x a toute temperature, qui a permis l'analyse du role determinant de la mise en ordre des anions c10 (a t = 24 k) sur l'etat fondamental (supraconducteur ou isolant) du compose organique unidimensionnel (tmtsf)#2c10#4. L'influence des deformations elastiques du reseau cristallin sur les proprietes geometriques de la surface fermi sont ainsi rapportees et correlees aux proprietes electroniques observees a basse temperature
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VAN, QUYNH ALEXANDRA. "Résonance magnétique nucléaire dans la phase mixte des composés organiques de la famille k-(BEDT-TTF)2CuX." Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10107.
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Nous presentons un ensemble de spectres obtenus par resonance magnetique nucleaire (rmn) du proton dans la phase supraconductrice de deux supraconducteurs organiques de structure voisine : -(bedt-ttf)#2cu(ncs)#2 et -(bedt-ttf)#2cun(cn)#2br. Dans le compose -(bedt-ttf)#2cu(ncs)#2 pour un champ applique perpendiculairement aux couches conductrices nous obtenons, dans la phase mixte, des formes de raie inattendues, tres differentes de celles prevues pour un reseau de vortex abrikosov triangulaire. En particulier, au-dessous d'une temperature t* qui depend de l'intensite du champ, nous observons une raie secondaire qui traduit un ecrantage diamagnetique bien plus important que celui attendu pour un reseau de vortex triangulaire. Nous montrons que ce sont les impulsions de champ radiofrequence qui, en perturbant violemment le reseau de vortex, conduisent a des conditions d'ecrantage particulieres. Une etude de ce phenomene pour des valeurs du champ comprises entre 0. 5 et 1 t montre qu'autour de 0. 82 t l'effet des impulsions de champ radiofrequence est maximal. Nous suggerons que cette valeur correspond a celle du champ de crossover dimensionnel du reseau de vortex. Nous estimons alors l'anisotropie #c/#a#b du compose entre 145 et 160. Le comportement aux basses temperatures de la nouvelle phase suggere, a l'instar des variations de la profondeur de penetration avec la temperature, que le gap supraconducteur de -(bedt-ttf)#2cu(ncs)#2 est anisotrope avec d'eventuelles lignes de nuds. Des mesures complementaires, notamment une etude du comportement de la phase secondaire en fonction de la duree des impulsions de champ radiofrequence, sont necessaires pour une meilleure comprehension de ce phenomene, inedit a notre connaissance. Une etude systematique des formes de raie du proton pour des temperatures inferieures a 4. 2 k dans le compose voisin -(bedt-ttf)#2cun(cn)#2br, dans un champ de 0. 8 t applique perpendiculairement aux plans conducteurs, nous a permis de determiner la profondeur de penetration #a#b(0) a 4920 100 a. Les variations lineaires de #a#b(t) aux basses temperatures indiquent que l'etat fondamental de ce compose ne peut etre decrit par un couplage bcs conventionnel isotrope.
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Faulmann, Christophe. "Conducteurs derives de metaux de transition : complexes moleculaires, polymeres, oxydes de cuivre." Toulouse 3, 1988. http://www.theses.fr/1988TOU30160.
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Demiralp, Ersan. "Prediction of structures and properties for organic superconductors." Thesis, 1996. https://thesis.library.caltech.edu/3387/1/Demiralp_e_1996.pdf.
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NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
The main contributions of this thesis to the field of organic superconductors are basically (a) the band structure calculations for the investigations of the conduction properties of [...] using 2-D Hubbard Model with Unrestricted Hartree-Fock (UHF) theory, (b) ab initio quantum mechanical calculations for the structural characterizations and the properties of the donors of the organic superconductors, (c) electron-transfer boat-vibration (ET-BV) mechanism for the superconductivity of these materials, (d) developing force fields for BEDT-TTF and BEDT-TTF+.
To provide a basis for understanding the puzzling electronic properties of the organic superconductor [...] (with Tc=10.4K), we carried out band calculations using the 2-D Hubbard Model with Unrestricted Hartree-Fock (UHF) theory. The electron transfer hopping interactions are from ab initio calculations and the Hubbard parameter (Uopt=0.678950 eV) is adjusted to fit Shubnikov-de Haas and magnetic breakdown experiments. The calculations lead to a two-band semi-metal with a momentum gap separating the electron and the hole bands. The anomalous experimental observations are explained in terms of BEDT-TTF related phonons coupling these two bands (lower temperature) and by anion related phonons (higher temperature). These results also provide a framework for describing the conduction properties of other such complexes.
The donors of all known one- or two-dimensional organic superconductors, X, are based on a core organic molecule that is either tetrathiafulvalene (denoted as TTF) or tetraselenafulvalene (denoted as TSeF) or some mixture of these two molecules. Coupling X, with appropriate acceptors, Y, leads to superconductivity. The oxidized form of X may be X+ or X2+ species in the crystal. Using ab initio Hartree-Fock (HF) calculations (6-31G** basis set), we show that BEDT-TTF deforms to a boat structure (C2 symmetry) with an energy 28 meV (0.65 kcal/mol) lower than planar BEDT-TTF (D2 Symmetry). On the other hand BEDT-TTF+ is planar. Performing ab initio quantum mechanical calculations (HF/6-31G**) also on the other donors of organic superconductors, we find that all known organic superconductors involve an X that deforms to a boat structure while X+ is planar. This leads to a coupling between charge transfer and the boat deformation phonon modes. We propose that this electron-phonon coupling is responsible for the superconductivity and predict the isotope shifts [...] for experimental tests of the electron-transfer boat-vibration (ET-BV) mechanism. We suggest that new higher temperature organic donors can be sought by finding modifications that change the frequency and stability of this boat distortion mode. Based on this idea we have developed similar organic donors having the same properties and have suggested that with appropriate electron acceptors they will also lead to superconductivity.
The highest transition temperature Tc organic superconductors all involve molecule BEDT-TTF coupled with an appropriate acceptor. The experimental structures exhibit considerable disorder in the outer rings and concomitant uncertainty in the structures of BEDT-TTF. We find that Hartree-Fock (6-31G** basis set) calculations leads to results within 0.01Å and 1° of experiment for the ordered regions allowing us to predict to composite structures expected to have this accuracy. We report optimized geometries and atomic charges for BEDT-TTF, BEDT-TTF+, and BEDT-TTF+1/2 that should be useful for atomistic simulations.
The vibrational levels of BEDT-TTF and BEDT-TTF+ have been only partially observed and assigned. In order to provide a complete consistent description of all levels, we carried out HF calculations for all fundamental vibrational frequencies of BEDT-TTF and BEDT-TTF+ and obtained the Hessians for these structures. With these Hessians and available experimental frequencies, we developed the force fields for the neutral and cation BEDT-TTF molecules by using Hessian-biased method.
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Kaiser, Stefan [Verfasser]. "Interplay of charge order and superconductivity : optical properties of quarter-filled two-dimensional organic conductors and superconductors / vorgelegt von Stefan Kaiser." 2010. http://d-nb.info/1008871702/34.
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Patterson, Donald Eugene. "Studies involving novel inorganic materials: I. The direct fluorination of diamond, high-temperature superconductors, and selected organic materials. II. The use of gem-cut cubic zirconia in the diamond anvil cell." Thesis, 1989. http://hdl.handle.net/1911/16279.
Full textAbstract:
The direct reaction of elemental fluorine with diamonds, YBa$\sb2$Cu$\sb3$O$\sb{\rm 7-x}$, and some unique organic materials has been studied. It has been found that diamonds (powder, slabs, and CVD films) can be directly fluorinated to a small extent using elemental fluorine under various reaction conditions. The reaction appears to proceed by fluorine attacking the diamond's more labile surface features such as the hydroxyl group. While the diamond surface is reactive to some extent, it is difficult to fully fluorinate this surface with elemental fluorine. Plasma fluorination seems to lead to the formation of CF terminal bonds on the diamond surface while high temperature direct fluorination leads to the formation of CF$\sb2$ and CF$\sb3$ terminal bonds. In oxidation resistance studies, the CF$\sb2$ and CF$\sb3$ terminal bonds lead to a more stable product than do the CF bonds.
The direct fluorination of the high temperature superconductor, YBa$\sb2$Cu$\sb3$O$\sb{\rm 7-x}$, leads primarily to the formation of a non-superconducting phase. This phase encapsulates the superconducting phase. Thus, there is no significant change in the fluorinated material's onset of critical temperature, but there is a significant decrease in the degree of magnetic shielding for the material as the amount of fluorination is increased. Initial attempts at synthesizing nitrofluorosuperconductors are presented.
We have successfully used direct fluorination techniques to yield improved properties for Velcro (made principally of polypropylene) and have had some success at fluorinating indan and PVC. The fluoro-Velcro shows enhanced lint repellent properties while maintaining its suppleness and other desirable properties. Perfluoroperhydroindan, a potential fluoroblood, has been prepared in small quantities using this novel treatment. PVC has been modestly fluorinated with the potential of carrying the fluorination to completion and should yield a superior product.
The use of cubic zirconia, an inexpensive diamond simulant, as high pressure/high temperature transmitting windows in the diamond anvil optical cell has been shown to be promising. Pressures nearing 20 kbars can be obtained in the cell using cubic zirconia anvils. The optical properties of cubic zirconia open up a region of the mid-IR that has been inaccessible with previous windows at these pressures. An FT-IR study of the high pressure effects on Fe(CO)$\sb6$($\mu$-CO)$\sb2$($\mu$-CH$\sb2$) is presented as proof. (Abstract shortened with permission of author.)
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Roth, Friedrich. "Electronic structure of selected aromatic hydrocarbon systems investigated with electron energy-loss spectroscopy." Doctoral thesis, 2012. https://tud.qucosa.de/id/qucosa%3A26700.
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Organic materials with fascinating/intriguing electronic properties have been the driving force for many research activities in the past, and in particular for important progress in materials science covering both new functional materials as well as theoretical developments. In addition, charge transfer, i. e., the addition or removal of charges to or from molecules in organic solids is one route to modify and control their electronic properties. Recently, the discovery of superconductivity in several alkali metal intercalated hydrocarbon systems (picene, phenanthrene, coronene and 1,2;8,9-dibenzopentacene) with rather high transition temperatures has opened a new chapter in organic material science as well as solid-state physics.
The search for a microscopic understanding of the mechanism that drives materials superconducting always has initiated a large number of scientific activities, and there are numerous examples where these activities have provided major advancement. A basic foundation of this understanding is the knowledge of the electronic properties of the material under investigation.
In this context, this thesis reports first, very detailed insight into the electronic structure of both undoped as well as potassium doped picene, coronene and 1,2;8,9-dibenzopentacene using electron energy-loss spectroscopy (EELS) as main experimental method. Additionally, also photoemission spectroscopy experiments have been performed to investigate the occupied electronic density of states close to the chemical potential. In order to learn more about the electronic structure we have compared the results we obtained from EELS and photoemission spectroscopy with theoretical calculations based on Density functional theory (DFT) using the local-density approximation (LDA).
We identify the peculiar case of very close lying conduction bands that upon doping harbour the electrons that form the Cooper-pairs in the superconducting state. Moreover, the presented data display substantial changes in the electronic excitation spectrum upon doping, whereas in the doped case the appearance of one new peak (for picene) and several new peaks (for coronene and 1,2;8,9-dibenzopentacene) in the former optical gap is reported. By using a Kramers–Kronig analysis (KKA) it is possible to gain information about the nature of this doping introduced excitations. In particular, in case of picene, the new low energy feature can be assigned to a charge carrier plasmon. Interestingly, this plasmon disperses negatively upon increasing momentum transfer, which deviates significantly from the traditional picture of metals based on the homogeneous electron gas. The comparison with calculations of the loss function of potassium intercalated picene shows how this finding is the result of the competition between metallicity and electronic localization on the molecular units.
Furthermore, core level excitation measurements show the reduction of the lowest lying C 1s excitation feature, which clearly demonstrates that potassium intercalation leads to a filling of the conduction bands with electrons. Additionally, the measurements of potassium intercalated 1,2;8,9-dibenzopentacene clearly indicate the formation of particular doped phases with compositions K_xdibenzopentacene (x = 1, 2, 3), whereas the data suggest that K_1dibenzopentacene has an insulating ground state with an energy gap of about 0.9 eV, while K_2dibenzopentacene and K_3dibenzopentacene might well be metallic, because of the absent of an energy gap in the electronic excitation spectra.
Interestingly, a comparison of the photoemission as well as EELS spectra of undoped 1,2;8,9-dibenzopentacene and pentacene reveal that the electronic states close to the Fermi level and the electronic excitation spectra of the two materials are extremely similar, which is due to the fact, that the additional two benzene rings in 1,2;8,9-dibenzopentacene virtually do not contribute to the delocalized pi molecular orbitals close to the Fermi level. This close electronic similarity is in contrast to the behavior upon potassium doping, where evidence for a Mott state has been reported in the case of pentacene.
A comparison of the low energy excitation spectra of chrysene with picene (phenacenes) as well as tetracene with pentacene (acenes) crystals reveal a significant difference between the former and the latter two materials. While for the phenacenes (zigzag arrangement) the excitation onset is characterized by up to five weak excitation features with only small anisotropy and without visible Davydov splitting within the a*, b*-planes, the acene (linear arrangement) spectra are dominated by a large excitation close to the onset and a sizable Davydov splitting. The presented data show further that the spectral shape of the pentacene excitation spectrum provides clear evidence for a large admixture of molecular Frenkel-type excitons with charge-transfer excitations resulting in excited states with a significantly mixed character. This conclusion is in good agreement with recent advanced calculations which predicted a charge-transfer admixture to the lowest singlet excitation which is significantly dependent upon the length of the acene molecules. Moreover, also for picene and chrysene we observe differences which point towards an increased charge-transfer contribution to the singlet excitation spectrum in the former.
Finally, investigations of the electronic properties of undoped and potassium doped chrysene, a close relative of picene, show that the doping introduced changes are in a similar range such as observed in case of picene. Interestingly, due to the analogy between the observed changes in the electronic structure upon potassium doping between chrysene and picene and further similarity in the crystal structure we speculate that chrysene is a promising candidate for another aromatic hydrocabon superconductor.
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Beyer, Rico. "Winkelaufgelöste Messungen der spezifischen Wärme des organischen Supraleiters beta''-(ET)2SF5CH2CF2SO3." Doctoral thesis, 2012. https://tud.qucosa.de/id/qucosa%3A26632.
Full textAbstract:
Im Jahr 1964 wurde eine Theorie der Supraleitung vorgestellt, welche Cooper-Paarbindungen mit nichtverschwindendem Gesamtimpuls berücksichtigt. Sie wird nach den maßgeblich beteiligten Physikern P. Fulde, R. A. Ferrell, A. I. Larkin und Y. N. Ovchinnikov als FFLO-Supraleitung bezeichnet [1, 2]. Aufgrund recht anspruchsvoller Voraussetzungen kommen nur wenige Festkörper-Systeme in Frage, die eine FFLO-Phase ausbilden könnten. Im Jahr 2007 konnte R. Lortz durch Messungen der spezifischen Wärme an dem organischen Supraleiter kappa-(ET)2Cu(NCS)2 einen soliden Nachweis für eine weitere thermodynamische Supraleitungs-Phase in hohen Magnetfeldern erbringen [3]. ET steht hierbei für Bis-(ethylen-dithiolo)-tetrathiafulvalen.
Die Hochfeld-Phase von kappa-(ET)2Cu(NCS)2 erfüllt alle bekannten Bedingungen für einen FFLO-Zustand. Diese Arbeit befasst sich mit der Erbringung eines gleichwertigen Beweises einer thermodynamischen Hochfeld-Supraleitungs-Phase in dem quasi-zweidimensionalen und vollständig organischen Supraleiter beta\'\'-(ET)2SF5CH2CF2SO3 durch hochauflösende Messungen der spezifischen Wärme. Darüber hinaus sollte durch eine präzise Ausrichtung der Probe zum Magnetfeldvektor die Feldorientierungsabhängigkeit der spezifischen Wärme und damit der supraleitenden Phasen bestimmt werden.
[1] - P. Fulde and R.A. Ferrell, Phys. Rev., 135:A550, (1964).
[2] - A.I. Larkin and Y.N. Ovchinnikov, Zh. Eksp. Teor. Fiz., 47:1136,(1964).
[3] - R. Lortz et al., Phys. Rev. Lett., 99:187002, (2007).
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Weiß, Herbert Dieter [Verfasser]. "Fermi surface studies on the organic superconductor k_63-(BEDT-TTF)2Cu[(CN)2]Br [kappa-(BEDT-TTF)]2CuN[(CN)2]Br and on the alkaline earth subnitride NaBa3N by means of magneto-quantum oscillations / vorgelegt von Herbert Dieter Wei." 2001. http://d-nb.info/961716959/34.
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