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1
Moore, Timothy David. "Andreev reflection at high magnetic fields." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624125.
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Dahliah, Diana Faraj. "Andreev Spectroscopy Measurement Of GaMnAs Spin Polarization." Miami University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=miami1344427042.
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Chauvin, Martin. "Les effets Josephson dans les contacts atomiques supraconducteurs." Paris 6, 2005. https://tel.archives-ouvertes.fr/tel-00107465v2.
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Seif, Burkhard E. R. "Chaos on quantum graphs with Andreev scattering." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=968415458.
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Chua, Kok Gnee. "Andreev interferometry with superconducting persistent current qubits." Thesis, Royal Holloway, University of London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.424914.
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Miyoshi, Yasuyuki. "Development of point-contact Andreev reflection spectroscopy." Thesis, Imperial College London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.441970.
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偉亞東 and Yadong Wei. "Resonant Andreev reflections in superconductor-carbon-nanotubedevices." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2000. http://hub.hku.hk/bib/B31242406.
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Abu, Jeib Hussein A. A. "Andreev Reflection Studies in GaMnAs/Nb Microstructure." Miami University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=miami1407425754.
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Andreev, Andriy. "Nonparametric statistical modeling of recurrent events : a Bayesian approach." Helsinki : University of Helsinki, 2000. http://ethesis.helsinki.fi/julkaisut/mat/rolfn/vk/andreev/.
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Sanches, José Eduardo Cardozo. "Moléculas de Andreev mediadas por férmions de Majorana /." Ilha Solteira, 2020. http://hdl.handle.net/11449/192099.
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Orientador: Antonio Carlos Ferreira SeridonioResumo: Estudou-se teoricamente um modelo composto por um fio de Kitaev na fase topológica com dois pontos quânticos (QDs - Quantum Dots), um em cada extremidade do nanofio. Desta forma, dois casos foram factíveis de análise, um deles com os estados ligados de Majorana (MBSs - Majorana Bound States) das bordas do fio acoplados a um único QD e o segundo em que se tem ambos os MBSs acoplados aos dois QDs. Para a primeira situação três condições foram estudadas, nas quais se verificou, na primeira, os perfis de férmions de Majorana não locais, dados pelo acoplamento entre o MBS e o QD mais próximo e, nas outras duas condições, dois perfis relacionados aos acoplamentos dos dois MBSs a um QD, em que se considerou também a superposição entre os MBS. Estes dois perfis são denominados de bowtie e diamond, já conhecidos na literatura, possuindo também experimentos que validam suas manifestações. No segundo caso, em que se tem o acoplamento dos dois MBSs aos dois QDs e que se considerou também amplitudes de superposição entre os férmions de Majorana, investigou-se a manifestação de estados moleculares mediados por tais férmions, pois o transporte eletrônico entre os QDs, no sistema proposto, se dá por meio do nanofio. Constatou-se padrões condizentes a níveis moleculares ligante e antiligante nas assinaturas dos estados ligados de Andreev (ABSs), originários da superposição dos MBSs, assim como nos níveis dos QDs que foram desdobrados após a formação molecular.
Mestre
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Webb, James Luke. "Crossed Andreev reflection in nanoscale ferromagnet-superconductor devices." Thesis, University of Leeds, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.577519.
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Non-local effects in nanoscale devices have been of recent interest in the study of both superconducting spintronic effects and study, use and detection of pure spin currents in the normal state such as utilised in the lateral or non-local spin valve (NLSV). These devices have potential in terms of lateral integration of spintronics to electronic systems and potentially for superconducting solid state quantum entanglement, from crossed or non-local Andreev refection (CAR). Work is presented on NLSV structures fabricated by electron beam lithography and DC magnetron sputtering with in-situ Ar" ion milling of two nanoscale ferromagnetic Py nanowire electrodes in contact with a perpendicular normal/superconducting metal track, inter-electrode separation close to the spin coherence length As or the BCS coherence length ~o. Preliminary work is also presented on fabrication by resist masked shadow deposition. Local and nonlocal transport measurements have been performed to characterise both superconducting and normal state processes. The normal state NLSV effect for a Cu/Py device has been measured and values are presented for As and spin polarisation P for tunnelling and Ohmic junctions. Measurements of electrode anisotropic magnetoresis- tance (AMR) are shown, aiming to create an ideal electrode anti parallel magnetisation to separate CAR from competing elastic cotunnelling (EC). Poor magnetic switching be- haviour was observed; the results of investigations performed to determine the cause for Py nanowire structures is presented in conjunction with micromagnetic simulation. Measurements taken at sub-lK are shown, with good evidence of CAR for PylAI devices. Distinction between CAR, EC and charge imbalance (Cl) is detailed through measurements as a function of injected current, temperature and magnetic field compar- ing to literature experiments and theoretical models. Evidence is presented of CAR in Ta, not previously observed. A proposal is made for a potential new geometry for realising non local effects for shorter coherence length superconductors. 3
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Naylor, Adam David. "Measuring spin polarisation with point-contact Andreev reflection." Thesis, University of Leeds, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.534829.
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Wei, Yadong. "Resonant Andreev reflections in superconductor-carbon-nanotube devices." Hong Kong : University of Hong Kong, 2000. http://sunzi.lib.hku.hk/hkuto/record.jsp?B22718679.
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Siqueira, Ezequiel Costa. "Transporte por reflexão de Andreev em pontos quânticos duplos acoplados a eletrodos supercondutores e ferromagnéticos." [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277834.
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Orientador: Guillermo Gerardo Cabrera OyarzunTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
Made available in DSpace on 2018-09-24T19:09:49Z (GMT). No. of bitstreams: 1 Siqueira_EzequielCosta_D.pdf: 16155551 bytes, checksum: 43337169b3f9ac0ffbe444e3859ff790 (MD5) Previous issue date: 2010
Resumo: Neste trabalho é estudado o transporte quântico em nanoestruturas híbridas compostas por pontos quânticos (PQ) duplos acoplados a eletrodos supercondutores (S) e ferromagnéticos (F). A primeira nanoestrutura, denotada por F - PQa - PQb - S consiste em dois PQs em série acoplados a um eletrodo ferromagnético e outro supercondutor. O segundo sistema, denotado por (F1, F2) - PQa - PQb - S consiste em dois PQs em série acoplados a dois eletrodos ferromagnéticos e um supercondutor. Através do método de funções de Green de não equilíbrio foram obtidas expressões para a corrente elétrica, condutância diferencial, densidade local de estados (LDOS) e a transmitância para energias inferiores ao gap supercondutor. Neste regime, o mecanismo de transmissão de carga é a reflexão de Andreev, a qual permite controlar a corrente através da polarização do ferromagneto. A presença de interações nos PQs é considerada usando um tratamento de campo médio. Para o sistema F - PQa - PQb - S, as interações tendem a localizar os elétrons nos PQs levando a um padrão assimétrico da LDOS reduzindo a transmissão através da nanoestrutura. Em particular, a interação intra PQ levanta a degenerescência de spin reduzindo o valor máximo da corrente devido ao desequilíbrio nas populações de spin up e spin down. Regiões de condutância diferencial negativa (CDN) aparecem em determinados valores do potencial aplicado, como resultado da competição entre o espalhamento Andreev e as correlações eletrônicas. Aplicando-se um potencial de gate nos pontos quânticos é possível sintonizar o efeito mudando a região onde este fenômeno ocorre. Para o sistema (F1, F2) - PQa - PQb - S observou-se que o sinal da magnetoresistência pode mudar de positivo para negativo mudando-se o sinal do potencial aplicado. Além disso é possível controlar a corrente no primeiro eletrodo mudando-se o valor do potencial no segundo ferromagneto. Este tipo de controle pode ser interessante do ponto de vista de aplicações desde que é um comportamento similar a um transistor. Na presença de interações nos PQs, observou-se novamente regiões de CDN para determinados valores do potencial aplicado mesmo para quando os ferromagnetos estão completamente polarizados. Desta forma, a interação entre supercondutividade e correlações eletrônicas permitiu observar fenômenos originais mostrando que este sistemas podem ser utilizados em aplicações tecnológicas futuras
Abstract: In this work we studied the quantum transport in two hybrid nanostructures composed of double quantum dots (DQD)s coupled to superconductor (S) and ferromagnetic (F) leads. The first nanostructure, denoted by F - QDa - QDb - S, is composed of a ferromagnet, two quantum dots, and a superconductor connected in series. In the second nanostructure, denoted by ( F1, F2) - QDa - Q Db - S, a second ferromagnetic lead is added and coupled to the first QD. By using the non-equilibrium Green's function approach, we have calculated the electric current, the differential conductance and the transmittance for energies within the superconductor gap. In this regime, the mechanism of charge transmission is the Andreev re°ection, which allows for a control of the current through the ferromagnet polarization. We have also included interdot and intradot interactions, and have analyzed their influence through a mean field approximation. For the F - QDa - QDb - S system the presence of interactions tend to localize the electrons at the double-dot system, leading to an asymmetric pattern for the density of states at the dots, and thus reducing the transmission probability through the device. In particular, for non-zero polarization, the intradot interaction splits the spin degeneracy, reducing the maximum value of the current due to different spin-up and spin-down densities of states. Negative differential conductance (NDC) appears for some regions of the voltage bias, as a result of the interplay of the Andreev scattering with electronic correlations. By applying a gate voltage at the dots, one can tune the effect, changing the voltage region where this novel phenomenon appears. In the (F1, F2) - QDa - QDb - S, we have found that the signal of the magnetoresistance can be changed through the external potential applied in the ferromagnets. In addition, it is possible to control the current of the first ferromagnet (F1) through the potential applied in the second one (F2). This transistor-like behavior can be useful in technological applications. In the presence of interaction at the dots it was observed the NDC effect even when the electrodes were fully polarized. The results presented in this thesis show that the interplay between the superconductor correlation and electronic interactions can give rise to original effects which can be used in future technological applications
Doutorado
Física da Matéria Condensada
Doutor em Ciências
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Iniotakis, C., N. Hayashi, Y. Sawa, T. Yokoyama, U. May, Y. Tanaka, and M. Sigrist. "Andreev bound states and tunneling characteristics of a noncentrosymmetric superconductor." American Physical Society, 2007. http://hdl.handle.net/2237/11288.
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Bretheau, L. "LOCALIZED EXCITATIONS IN SUPERCONDUCTING POINT CONTACTS: PROBING THE ANDREEV DOUBLET." Phd thesis, Ecole Polytechnique X, 2013. http://tel.archives-ouvertes.fr/tel-00772851.
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L'effet Josephson décrit le couplage cohérent entre supraconducteurs et le supercourant qui en résulte. D'un point de vue microscopique, il découle de l'existence d'états de quasiparticules discrets, localisés au niveau du lien faible, les états liés d'Andreev. Ils viennent en doublets dans chaque canal de conduction du lien faible, avec des énergies et supercourants opposés. Chaque doublet d'Andreev donne lieu à quatre états: l'état fondamental \left|-\right\rangle et l'état excité \left|+\right\rangle , avec une parité paire, et les états excités impairs \left|\uparrow\right\rangle et \left|\downarrow\right\rangle . Est-il possible d'exciter les doublets Andreev? Cette thèse décrit deux séries d'expériences conçues pour répondre à cette question en utilisant l'élément Josephson le plus élémentaire, un contact atomique entre deux électrodes supraconductrices. Dans une première expérience, nous avons observé et caractérisé les états excités impairs \left|\uparrow\right\rangle et \left|\downarrow\right\rangle . Comme attendu pour un système dégénéré en spin, ils ne portent pas de supercourant. Dans cette expérience, l'excitation n'était pas contrôlée mais dû au piégeage spontanée de quasi-particules parasites dans l'un des états d'Andreev. Sous certaines conditions, le temps de vie mesuré de ces états impairs peut dépasser 100 µs. La deuxième expérience est une spectroscopie photonique des états d'Andreev. Elle a été effectuée en utilisant une junction Josephson en tant qu'émetteur et détecteur microonde. Les transitions d'Andreev observées correspondent à des excitations depuis l'état fondamental \left|-\right\rangle vers l'état excité paire \left|+\right\rangle , et sont bien décrites par notre modèle quantique. Ce résultat ouvre la voie à la manipulation cohérente de ce système à deux niveaux. L'observation directe de l'état excité d'Andreev, soit par injection de quasiparticules soit par absorption de photons, conforte la théorie mésoscopique de l'effet Josephson. Cela démontre que, en plus de la différence de phase, chaque canal d'un lien faible Josephson possède un degré de liberté fermionique interne similaire à un spin un-demi.
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Checkley, Chris. "Andreev interferometry of flux qubits driven by radio frequency field." Thesis, Royal Holloway, University of London, 2009. http://repository.royalholloway.ac.uk/items/3cad7ac1-cda2-3276-c635-8a4eef474b9f/10/.
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In this thesis we present the continuing work done examining a system in which an Andreev interferometer is used to probe the state of a flux qubit. In particular, we show that the back action of the interferometer on the qubit is low enough that an energy gap can still be observed in the qubit, and present the first experimental evidence of resonant excitation of a flux qubit detected using an Andreev interferometer. We begin by discussing the theory of flux qubits and Andreev interferometers individually. We then go on to examine what happens when with these two types of structures are combined, with particular attention being paid to the consequences for the coherence time of the qubit. We then discuss the practical elements of the experiment, notably the development of a tri-layer resists system that can be used to create high quality mesoscopic structures. We present the experimental results, which show the evidence for resonant excitation of a qubit detected using an Andreev interferometer. The quality of these resonances suggests that the system has a coherence time of less than 1ns. To conclude we examine some ways in which we believe the system can be improved in order to allow more detailed spectroscopic and time resolved measurements.
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Leibon, Gregory. "Random delaunay triangulations, the Thurston-Andreev theorem, and metric uniformization /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1999. http://wwwlib.umi.com/cr/ucsd/fullcit?p9936832.
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Bretheau, Landry. "Localized Excitations in Superconducting Atomic Contacts : Probing the Andreev Doublet." Palaiseau, Ecole polytechnique, 2013. http://pastel.archives-ouvertes.fr/pastel-00862029.
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Cette thèse décrit deux expériences mettant en lumière l'existence d'un degré de liberté fermionique dans l'effet Josephson: le doublet d'Andreev. Elles sont toutes les deux réalisées sur l'élément Josephson le plus élémentaire qui soit, un contact atomique entre deux électrodes supraconductrices. Dans la première, nous avons observé la disparition du supercourant, qui traduit le piégeage spontané d'une quasiparticule dans l'un des deux états liés d'Andreev. Dans la seconde, nous avons réalisé la spectroscopie photonique de ce système à deux niveaux, en utilisant une jonction Josephson à la fois en tant qu'émetteur et détecteur microonde. On peut bien rendre compte des spectres observés avec un modèle spin-boson incluant le doublet d'Andreev et un mode électromagnétique de l'environnementThis thesis discusses two experiments highlighting the existence of a fermionic degree of freedom in the Josephson effect: the Andreev doublet. They are both performed on the most basic Josephson element, a one-atom contact between two superconducting electrodes. In the first one, we observed the disappearance of the supercurrent, which reflects the spontaneous trapping of a quasiparticle in one of two Andreev bound states. In the second experiment we achieved the photon-absorption spectroscopy of this two-level system, using a Josephson junction as an integrated on-chip microwave emitter and detector. The observed spectra are well accounted for by a spin-boson model including the Andreev doublet and an electromagnetic mode of the environment
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Janvier, Camille. "Coherent manipulation of Andreev Bound States in an atomic contact." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS217/document.
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Des états électroniques localisés apparaissent dans les liens faibles entre électrodes supraconductrices : les états d’Andreev. Les expériences présentées dans cette thèse explorent les propriétés de cohérence quantique de ces états, en utilisant comme liens faibles des contacts à un atome entre des électrodes d’aluminium. Les contacts atomiques sont intégrés dans une cavité microonde qui permet à la fois de les isoler et de les sonder.Dans une première série d’expériences, il est montré qu’on peut utiliser les états d’Andreev pour définir un bit quantique, le « qubit d’Andreev », qu’on contrôle à l’aide d’impulsions micro-onde.Les mesures des temps de vie de cohérence de ce qubit sont analysées en détail.Dans une deuxième série d’expérience,l’interaction entre le qubit d’Andreev et le résonateur micro-onde est utilisée pour quantifier le nombre de photons présents dans le résonateur en fonction de la puissance d’impulsions microonde à sa fréquence propre.Enfin, des sauts quantiques et des sauts de parités ont observés dans des mesures continues de l’état du qubit d’AndreevLocalized electronic states, called Andreev bound states, appear in weak-links placed between superconducting electrodes. The experiments presented in this thesis explore the coherence properties of these states. Single atom contacts between aluminum electrodes are used as weak links. In order to isolate and probe these states, the atomic contacts are integrated in amicrowave cavity.In a first series of experiments, it is shown that Andreev states can be used to define a quantumbit, “the Andreev qubit”, which is controlled using microwave pulses.Measurements of the lifetime and coherence time of this qubit are thoroughly analyzed.In a second series of experiments, the interaction between the Andreev qubit and the microwave cavity are used to determine the number of photons present in the cavity as a function of the power of microwave pulses at its eigenfrequency.Finally, quantum and parity jumps are observed in continuous measurements of the state of the Andreev dot
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Le, calvez Kévin. "Signatures of a 4pi periodic Andreev bound state in topological Josephson junctions." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY099/document.
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Les isolants topologiques 3D sont un nouvel état de la matière décrit par un volume iso-lant électriquement et recouvert par des états de surface métalliques. Une jonction Joseph-son topologique (TJJ) formée autour de ces états de surface peut théoriquement contenirun mode lié d’Andreev ayant une périodicité doublée par rapport aux modes liés d’An-dreev conventionnels 2p périodiques. Le mode d’Andreev 4p périodique serait la briqueélémentaire de l’ordinateur quantique topologique. Ainsi, nous étudions la dynamique dece mode particulier lors de mesures de Shapiro sur des jonctions Josephson fabriquées surdes isolants topologiques à base de bismuth.A?n d’identi?er les e?ets d’un mode 4p-périodique dans une mesure de Shapiro, nousutilisons un model phénoménologique permettant de simuler la caractéristique courant-tension d’une TJJ lors de telles mesures. Nous prédisons deux signatures du mode 4p-périodique et estimons leur robustesse face aux e?ets de chau?age par e?et Joule et face àun modèle d’empoisonnement thermiquement activé du mode 4p-périodique.Par des mesures de Shapiro, nous étudions la dynamique des TJJ basées sur le matériausimple qu’est le Bi2Se3. L’observation des deux mêmes signatures précédemment anticipéespar nos simulations, à savoir un ordre d’apparition non conventionnel des pas de Shapiroainsi que la persistance d’un supercourant à la fermeture du plateau de Shapiro n = 0prouve la présence d’un mode 4p-périodique.Notre étude s’est également portée sur un autre isolant topologique le BiSbTeSe2. Nousavons e?ectué sa croissance par cristallisation liquide-solide et avons mis en évidence,par des mesures d’interférométrie supraconductrice une supraconductivité de surface sanstransport électronique par le volumeThree dimensional topological insulators (3D TI) are a new state of matter composedof an electrically insulating bulk covered by metallic surface states. Theoretically, a topo-logical Josephson junction composed of these surface states can host an Andreev Boundstate (ABS) that has twice the periodicity of the conventional 2p periodic ABSs. The4p periodic ABS is expected to be the building block of topological quantum computing.Therefore, we study the dynamic of this particular ABS by performing Shapiro measure-ment on Josephson junctions built with bismuth based 3D TI.To identify the e?ects of a 4p periodic ABS in a Shapiro measurement, we use a phe-nomenological model that simulates the voltage-current characteristics of a TJJ. We predicttwo signatures of the 4p periodic ABS and estimate their robustness against Joule heatingand thermally activated quasiparticle poisoning of the 4p periodic mode.We study the Josephson junctions dynamics by performing Shapiro measurements onjunctions built on Bi2Se3. We observe the two previously anticipated signatures, whichare the non-conventional appearance order of the Shapiro steps and the remaining of asupercurrent at the closing of the Shapiro step n = 0. They prove the presence of a 4pperiodic ABS.We also study the topological insulator BiSbTeSe2 that we have grown by using themelting growth method. By superconducting interferometric measurements, we show asuperconducting surface transport without bulk electronic conduction
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Usman, Irham Tri Muharram. "Investigating inhomogeneous FM at SC/FM interfaces using point-contact Andreev spectroscopy." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/12254.
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The unconventional long range (m=1) spin triplet proximity effect is theorised to be created at a Superconductor/Ferromagnet (SC/FM) interface that is magnetically inhomogeneous and provides the conditions for spin mixing. Many experimental and theoretical works have identified the existence of the m=1 spin triplet state using Josephson junctions to show how the critical current does not diminish significantly in a thick FM layer, (thickness being relative to the decay length of a Cooper pair in an FM). In this thesis the challenge was to examine single SC/FM, interfaces via point-contact Andreev Reflection spectroscopy (PCARS), to see if it were possible to find clear signatures of the spin mixing or spin scattering conditions that facilitates formation of the spin triplet state. PCARS measurements were performed on Ho single crystals and thin films as a function of contact resistance. The results show an anomalous decrease of the polarisation parameter and an increase in interface scattering parameter as the contact resistance decreases. This is interpreted in terms of the tip experiencing a region in which some form of spin mixing or spin scattering dominates. Measurements of Ni0.19Pd0.81 spectra were also taken as a function of contact resistance but the change of polarisation and scattering parameter that was observed in the Ho samples was not observed here. PCARS temperature measurements were also taken for Ni0.03Pd0.97 to investigate if spin fluctuations close to TC could provide the magnetic inhomogeneity required for spin-mixing. However the trend in the results proved inconclusive. This is likely due to broadening that result in the fitting procedure, and the extremely small polarisation in these samples. During the course of the thesis I contributed to the development of the spectral fitting routines and examined the challenges associated with three and four parameter fitting, degenerate fits and series resistance.
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Rolet, Serge. "Les récits de Leonid Andréïev (une poétique de l'angoisse)." Paris 4, 1995. http://www.theses.fr/1994PA040376.
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Dans les récits de l. Andreev, l'invariant thématique majeur est l'angoisse. La structure du récit s'écarte de celle de la nouvelle classique. Le modèle du monde de l'auteur est un refus du rationalisme : l'absolu est dans le malIn l. Andrejev's short stories, the main constant theme is anguish. The structure of the narrative diverges from that of the classical short story. The writer's model world is a refusal of rationalism: the absolute lies in the nothingness
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Iagallo, Andrea. "Observation of metastable states in a superconducting Josephson circuit using an Andreev interferometer." Thesis, Royal Holloway, University of London, 2011. http://repository.royalholloway.ac.uk/items/4910e2b0-d123-a4f6-7b95-d60288a9b58c/10/.
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We report on measurements of macroscopic quantum states in superconducting Josephson circuits using a highly sensitive hybrid quantum interferometer as the readout probe. The investigated Josephson circuit is one of the leading candidates as solid-state qubits (persistent current qubit), which are known to exhibit macroscopic quantum states with atomic-like properties. The readout device is a modified Andreev interferometer with semi-metallic normal segment in a “folded" geometry, and is designed to reduce the back action during measurement, as well as minimising the electromagnetic coupling between the circuit and the environment. A pulsed lock-in technique has been developed to perform continuous readout of the superconductor phase difference using pulse lengths down to 10 ns. The technique enables to control the energy of the probing quasiparticles in the normal segment of the interferometer, which in turn allows to control of the supercurrent owing in the SNS junction and prevents electron heating of the normal segment. An experimental set-up was designed and installed in a dilution fridge consisting of shielded wiring, magnetic screens, RF tight sample holder and printed circuit board to allow the injection of high frequency excitation signals, while minimising the environment effect on the qubit through careful electrical filtering. The effect of strong RF irradiation on Andreev interferometers allowed us to estimate the response time of the readout device to be less than 40 ps. The measurements show that two macroscopically distinct metastable states exist when the device is biased at the qubit degeneracy point, between which the system makes transitions that can be continuously monitored. Real time kinetics of the system has been investigated at different magnetic fluxes, pulse parameters, temperature and RF radiation. Based on statistical analysis of the transitions, we argue that the metastability is connected with macroscopic quantum tunnelling effects rather than thermal excitation. The experimental data support the hypothesis of a large low frequency noise causing low transition rates.
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Jacobs, Arne. "Andreev-Streuung, Josephson-Bloch-Oszillationen und Zener-Tunneln in Heterokontakten aus Normal- und Supraleitern." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=971768846.
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Freamat, Mario Vadim. "NORMAL AND SPIN POLARIZED TRANSPORT IN HIGH-TEMPERATURE SUPERCONDUCTOR TUNNELING JUNCTIONS." UKnowledge, 2004. http://uknowledge.uky.edu/gradschool_diss/426.
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One of the challenges facing condensed matter physics nowadays is to understand the electronic structure of high temperature superconductors. This dissertation compiles our contribution to the experimental information concerning this subject. Tunneling conductance spectroscopy a technique capable of probing the electronic density of states in hybrid structures was used to study the current and spin transport properties across junctions between metallic counterelectrodes and Bi2Sr2CaCu2O8- (BSCCO) crystals. Since in these structures the transport is mediated by transmission channels depending on superconductive characteristics, the energy resolved density of states is a signature of the mechanism of superconductivity. For instance, one can observe the superconductive energy gap and the behavior of subgap bound states due to phase sensitive Andreev reflections at the junction interface. In particular, tunneling spectroscopy makes possible the observation of the LOFF state characterized by the coexistence of superconductivity and magnetism. Cuprates like BSCCO are highly anisotropic materials and their superconductivity is almost two dimensional, being confined in the CuO2 planes. Therefore, our junctions combine monocrystals of underdoped samples of BSCCO with various thin film counterelectrodes normal metal (Ag), conventional superconductor (Pb) and ferromagnetic metal (Fe) deposited perpendicular onto the cuprate ab-plane (CuO2 plane). We performed measurements on Ag/BSCCO junctions for two current injection directions into the same crystal. We observed that, near the 110 crystal surface, the conductance spectra show a high zero bias peak (ZBCP) which is a manifestation of zero energy Andreev bound states due to an anisotropic superconductive order parameter. Near the 100 surface, the ZBCP is largely suppressed. This is consistent with a predominantly 2 2 x y d - -wave pairing symmetry. In some cases, the ZBCP splits or decreases in amplitude at low temperatures. This is consistent with the existence of a subdominant s-wave (or xy d ) resulting in a mixed d is + state which breaks time reversal symmetry (BTRS). Since we observe this phenomenon in the underdoped case, we do not confirm the possibility of a quantum critical point close to the optimal doping. Our Pb/BSCCO spectra contradict the theory explaining the BTRS by proximity effect. The Fe/BSCCO junctions measure the effect of spin polarization. We explain the recorded 4-peak asymmetric structure by the combined effect of a spin independent BTRS state and a spin filtering exchange energy in the barrier responsible for a large ZBCP splitting. The LOFF state was observed in the proximity region induced on the ferromagnetic side of multilayered-Fe/Ag/BSCCO structures. As expected for the LOFF order parameter, the spectra develops coherent damped oscillations with the Fe layer thickness probing different regions. The magnitude and sign of the oscillation depends on the energy. The conductances at energy zero or equal to the superconductive gap are modulated in antiphase proving that the order parameters takes successively positive and negative values. Changing the junction orientation with 4 p , results in an opposite behavior for the same distance. The maximal amplitudes in one direction is replaced by minima, showing that, besides space, the LOFF state modulation depends on the phase of the high temperature order parameter inducing the proximity
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Assunção, Maryzaura de Oliveira. "Reflexão de Andreev cruzada via dubleto de Autler-Townes em uma junção ponto quântico - supercondutor." Universidade Federal de Uberlândia, 2017. http://dx.doi.org/10.14393/ufu.te.2018.3.
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FAPEMIG - Fundação de Amparo a Pesquisa do Estado de Minas GeraisO conhecimento teórico e experimental acumulado nas últimas décadas sobre pontos quânticos semicondutores (PQs) impulsiona o surgimento de um grande número de propostas atuais de utilizá-los em sistemas híbridos. A habilidade de controlar suas propriedades optoeletrônicas, bem como o domínio de sofisticadas técnicas de fabricação, tornaram-os candidatos ideais para formar junções com supercondutores (SCs), cujas características individuais são também notáveis. Essas junções podem ser simples, com um único PQ acoplado a um SC, ou múltiplas: a conexão de dois terminais SCs através de um PQ (junção tipo Josephson) e a junção de dois PQs através de um SC. Esta última forma um separador de pares de Cooper, dispositivo sugerido como fonte de partículas emaranhadas, que depende fundamentalmente da ocorrência de reflexão de Andreev cruzada (CAR) nas interfaces da junção. Junções de PQs com SCs e com supercondutores topológicos também tem sido propostas em sistemas de dois níveis formando qubits para a computação quântica trivial e topológica. Embora o estudo das junções PQ-SC esteja em evidência atualmente, a revisão da literatura mostra que a análise do regime transiente foi pouco explorada. Por isso, abordamos neste trabalho o transporte de cargas em uma junção PQ-SC-PQ com resolução temporal. Utilizando técnicas de função de Green de não-equilíbrio, particularmente, o formalismo de Kadanoff-Baym, escrevemos um conjunto de equações diferenciais acopladas, solucionado numericamente. Analisando as oscilações de Rabi que surgem na evolução temporal da corrente elétrica e das ocupações dos PQs, fomos capazes de identificar assinaturas de mecanismos de espalhamento através da junção, isto é, o tunelamento direto e a CAR. Adicionalmente, propusemos a expansão deste sistema pela sua inserção na estrutura de um fotodiodo, aplicando luz laser sobre um dos PQs. Os resultados mostram que ocorre a separação dos níveis opticamente excitados em dubletos de Autler-Townes, para acoplamentos fracos entre os PQs. Consequentemente, é observada a ocorrência de CAR, mediada pelo laser aplicado, através dos níveis que compõe o dubleto. Os resultados tem dependência também com a tensão fonte-dreno aplicada ao dispositivo, que pode estar no limite de bias alta (HB) ou zero (ZB). Este é o primeiro trabalho a analisar a separação de pares de Cooper assistida por fótons em uma junção PQ-SC-PQ, em regime de não-equilíbrio. Embora os resultados experimentais ainda sejam escassos, a inclusão de um SC em um fotodiodo de PQs híbrido permite novos mecanismos de formação de fotocorrente, abrindo novas possibilidades de aplicações desse sistema.
The theoretical and experimental knowledge accumulated in the last decades on semiconductors quantum dots (QDs) impulses the emergence of many current proposals for using them in hybrid systems. The ability to control their optoelectronic properties, as well as the control of fabrication techniques, made them the perfect candidates to compose junctions with superconductors (SCs), whose individual characteristics are also remarkable. These junctions can be simple, with a single QD coupled to a SC, or multiple: a connection of two superconducting terminals through a QD (a Josephson-like junction) and the junction of two QDs through a SC. The latter is known as a Cooper-pairs splitter, a device suggested as a source of entangled particles, for which is required the occurrence of crossed Andreev reflection (CAR) on the interfaces of the junction. Junctions of QDs with SCs and with topological SCs have also been proposed in two-level systems as qubits for both trivial and topological quantum computation. Despite the study of QD-SC junctions being currently in evidence, the literature review shows that the analysis of transient regime was little explored. Therefore, we address in this work the topic of time-dependent charge transport in a QD-SC-QD junction. By using non-equilibrium Green functions techniques, particularly, the Kadanoff-Baym formalism, we write down a set of coupled differential equations, which is numerically solved. Examining the Rabi oscillations that appears on the time evolution of electric current and QDs occupations, we were able to identify signatures of the scattering mechanisms through out the junction, i. e., direct tunnelling and CAR. Additionally, we propose to use this system as a photodiode, with the aid of a laser beam over one of the QDs. The results show the splitting of the optically excited states in Autler- Townes doublets, for a weak coupling between the QDs. Hence, CAR mediated by the applied laser was observed through the energy levels that compose the doublet. The results depend also with the source-drain potential applied to the device, which can be high bias (HB) or zero bias (ZB). The present work is the first to analyse the splitting of Cooper pairs assisted by photons in a QD-SC-QD junction, in nonequilibrium regime. Although the experimental results are still sparse, the inclusion of a SC in a QD hybrid photodiode allows new mechanisms of photocurrent formation, creating possibilities in future applications.
Tese (Doutorado)
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Sanders, Jeff T. "Spin polarization measurements and sensor applications in thin films and carbon nanotube-based devices." [Tampa, Fla] : University of South Florida, 2006. http://purl.fcla.edu/usf/dc/et/SFE0001711.
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Pandey, Preeti [Verfasser], and D. [Akademischer Betreuer] Beckmann. "Andreev processes in two-terminal and multiterminal graphene based hybrid junctions / Preeti Pandey ; Betreuer: D. Beckmann." Karlsruhe : KIT-Bibliothek, 2020. http://d-nb.info/1212512537/34.
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Dassonneville, Bastien. "Dynamics of Andeev states in a normal metal-superconductor ring : supercurrent fluctuations and spectroscopy of the minigap." Phd thesis, Université Paris Sud - Paris XI, 2014. http://tel.archives-ouvertes.fr/tel-01011558.
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A SNS junction made of two superconducting (S) electrodes separated by a normal (N) metal carries a non-dissipative current whose amplitude depends on the phase difference between the superconductors. The equilibrium properties of this system have been recently explored and are now well understood. The dynamics is still an open question: how does the current-phase relation evolves with a high-frequency phase modulation? What are the mechanisms and characteristic times that govern this evolution?To probe the dynamics of Andreev states, we measured the response of a phase($ \varphi $)-biased NS ring. The current response at frequencies $ f $ ranging from 200 MHz up to 14 GHz yields the magnetic susceptibility $ \chi(\varphi,f) $ whose real part $ \chi' $ gives the the non-dissipative response while the imaginary part $ \chi'' $ reveals the dissipation. Susceptibility is accessed by the modification of a superconducting resonator coupled to the NS ring.As expected, $ \chi' $ is simply the phase derivative of the supercurrent at low frequency, thus revealing the current-phase relation. More strikingly, we observed the emergence of two contributions at high-frequency. The first one is related to the relaxation of populations driven out-of-equilibrium by the excitation. It is associated with supercurrent noise. The second one corresponds to induced transitions. According to our analysis of the experiment, its phase dependence is accounting for by taking into account selection rules. It should also allows to perform the minigap spectroscopy. These results show that such finite frequency measurements reveal properties of SNS junctions that can not be accessed by standard transport experiments.
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Brunetti, Aldo [Verfasser], Reinhold [Akademischer Betreuer] Egger, and Dagmar [Akademischer Betreuer] Bruß. "Josephson current and Andreev level dynamics in nanoscale superconducting weak links / Aldo Brunetti. Gutachter: Reinhold Egger ; Dagmar Bruß." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2014. http://d-nb.info/1063699754/34.
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Minott, Dutch Henry. "The design and implementation of a point-contact Andreev reflectivity probe for measuring the spin polarization of materials /." Available to subscribers only, 2005. http://proquest.umi.com/pqdweb?did=1079667631&sid=10&Fmt=2&clientId=1509&RQT=309&VName=PQD.
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Brunetti, Aldo [Verfasser], Reinhold Akademischer Betreuer] Egger, and Dagmar [Akademischer Betreuer] [Bruß. "Josephson current and Andreev level dynamics in nanoscale superconducting weak links / Aldo Brunetti. Gutachter: Reinhold Egger ; Dagmar Bruß." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2014. http://nbn-resolving.de/urn:nbn:de:hbz:061-20141204-103716-7.
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Dai, Zhenting. "Coherent and Dissipative Transport in Metallic Atomic-Size Contacts." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/19880.
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Thin-film niobium mechanically controlled break junctions and resistively shunted niobium mechanically-controlled break junctions were developed and successfully microfabricated. Using these devices, high-stability atomic size contacts were routinely produced and investigated both in the normal and superconducting states. Investigations of the two-level conductance fluctuations in the smallest contacts allowed the calculation of their specific atomic structure. Embedding resistive shunts close to the superconducting atomic-sized junctions affected the coherence of the electronic transport. Finally, point contact spectroscopy measurements provide evidence of the interaction of conduction electrons with the mechanical degrees of freedom of the atomic-size niobium contacts.
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Das, David Hari. "History writing and late Muscovite court culture : a study of Andrei Lyzlov's History of the Scythians /." Thesis, Connect to this title online; UW restricted, 1991. http://hdl.handle.net/1773/10509.
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Andreev, Darja [Verfasser], Aline [Akademischer Betreuer] Bozec, and Falk [Gutachter] Nimmerjahn. "The impact of the C-type lectin receptor Mincle on osteoclast-mediated bone remodeling / Darja Andreev ; Gutachter: Falk Nimmerjahn ; Betreuer: Aline Bozec." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2020. http://d-nb.info/1222739461/34.
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Szewczyk, Adam. "Supercurrents in a Topological Josephson Junction with a Magnetic Quantum Dot." Thesis, Linnéuniversitetet, Institutionen för fysik och elektroteknik (IFE), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-79327.
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The purpose of this master thesis is to investigate theoretically the influence of a nanomagnet on the Josephson effect displayed by phase biased point contacts consisting of topological superconductors. The device is modeled using the nonequilibrium Keldysh Green’s function technique. First, the Gor’kov Green’s functions are calculated. From these Green’s functions, the quasi-classical ones, relevant for energies around the Fermi energy, are obtained. Transport properties such as charge currents are calculated and analyzed in terms of the junction’s density of states displaying Andreev and Majorana states. The combination of the nanomagnet coupling and the spin-momentum locking of the topological superconductors generates a magneto-electric effect causing the supercurrent to depend strongly on the nanomagnet’s direction.
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Sarghi, Georgian. "The Circle Packing Theorem." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18804/.
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Il teorema di Koebe-Andreev-Thurston concerne l'esistenza di impacchettamenti di cerchi con un dato grafo di contatto.
In questo lavoro presentiamo una dimostrazione elementare di tale teorema, insieme a qualche esempio di applicazione. Descriveremo, nel terzo capitolo, la congettura di Thurston sull'approssimazione di mappe conformi tamite impacchettamenti di cerchi e daremo una dimostrazione del teorema del separatore planare basata sul teorema di Koebe-Andreev-Thurston.
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Marsh, Richard. "Superconducting phase coherent electron transport in nano-engineered ferromagnetic vortices." Thesis, Royal Holloway, University of London, 2013. http://repository.royalholloway.ac.uk/items/66b15a59-0b9f-4e68-b0aa-47e93f77349a/6/.
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This thesis presents an experimental study of the superconducting proximity effect in sub-micrometer sized ferromagnetic discs. Such discs belong to a class of mesoscopic ferromagnets intermediate between microscopic magnets with dimensions below about 10nm that behave as single giant spins and macroscopic structures that are larger than approximately 1 micrometer where domains are formed to minimise stray fields. The magnetic structure of mesoscopic magnets is strongly dependent on their geometric shape, allowing for purposeful engineering of magnetic structures using modern lithographic techniques. The ground magnetic state of mesoscopic ferromagnetic discs is the magnetic vortex where unusual time-asymmetric triplet superconductivity is predicted to exist and survive up to the non-magnetic coherence length, that is orders in magnitude larger than the ferromagnetic singlet coherence length. Magnetic Force Microscopy (MFM) was used to directly study the magnetic structure of the discs. To detect the proximity effect in the vortices, Andreev interferometers were used with normal parts replaced with mesoscopic ferromagnetic discs in the magnetic vortex state. The samples were fabricated using electron-beam lithography and a modified shadow evaporation technique developed within this project, allowing the whole structure to be made with highly precise alignment, without breaking vacuum and avoiding redundant ferromagnetic elements disturbing the magnetic vortices. Observations were made of superconducting phase periodic oscillations in the conductance of the Andreev interferometers. Such oscillations provide unambiguous evidence of phase coherent electron transport through the ferromagnetic vortex. Finally, further experiments are discussed that would provide a more detailed understanding of the long range proximity effect in SFS junctions.
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Kuorelahti, J. (Juri). "On the motion of objects immersed in Fermi liquids." Doctoral thesis, Oulun yliopisto, 2019. http://urn.fi/urn:isbn:9789526223056.
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Abstract Interacting many-body problems are central to most fields of physics. In condensed matter physics, the systems of interest consists of a number of bodies on the order of Avogadro's constant, ~10²³. The precise modeling of such systems is usually impossible. Under certain circumstances however, even these problems can become tractable. One such circumstance is that of a Fermi liquid. At sufficiently low temperatures, in describing the dynamics of a system of interacting fermions, it is possible to forgo description of the fermions themselves, and instead concentrate on the collective excitations of the entire fermion system. These collective excitations are called quasiparticles. In this thesis we study two phenomena related to the motion of objects in a Fermi liquid. First, we study the transmission of transverse oscillations through a thin film of normal Fermi liquid. The dynamics of normal Fermi liquid are described by Landau's Fermi liquid theory. Landau's theory predicts the existence of new modes of sound under conditions where sound ordinarily would not propagate. Using the equations of motion for the Fermi liquid quasiparticles, we calculate the linear response of a Fermi liquid film to the transverse oscillations of a planar substrate under a wide range of conditions. We present the linear response in terms of the film's acoustic impedance and study the effects of quasiparticle collisions and of the Fermi liquid interactions. The second phenomenon we study is the supercritical motion of a wire in a superfluid Fermi liquid. The prevailing assumption is that if the velocity of an object moving in a superfluid Fermi liquid surpasses a characteristic critical velocity, the object experiences a sudden onset of viscous forces. This viscosity is caused by the escape of quasiparticles, produced by pair breaking on the surface of the object, into the surrounding superfluid. We study Andreev reflection of the quasiparticles by the surrounding superfluid flow field, and modifications to the flow caused by pair breaking, as possible mechanisms for low-dissipation motion above the critical velocityOriginal publications The original publications are not included in the electronic version of the dissertation. Kuorelahti, J. A., Tuorila, J. A., & Thuneberg, E. V. (2016). Fermi liquid theory applied to a film on an oscillating substrate. Physical Review B, 94(18). https://doi.org/10.1103/physrevb.94.184103 Kuorelahti, J. A., & Thuneberg, E. V. (2018). Two-parameter boundary condition applied to transverse acoustic impedance of a Fermi liquid. Journal of Physics: Conference Series, 969, 12010. https://doi.org/10.1088/1742-6596/969/1/012010 http://jultika.oulu.fi/Record/nbnfi-fe2018060425173 Kuorelahti, J. A., Laine, S. M., & Thuneberg, E. V. (2018). Models for supercritical motion in a superfluid Fermi liquid. Physical Review B, 98(14). https://doi.org/10.1103/physrevb.98.144512 http://jultika.oulu.fi/Record/nbnfi-fe2018112148794
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Jehl, Xavier. "Bruit de grenaille dans les jonctions métal normal/supraconducteur." Université Joseph Fourier (Grenoble), 1999. http://www.theses.fr/1999GRE10126.
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Nous avons construit un dispositif permettant de mesurer le bruit de grenaille dans des echantillons de basse impedance, avec des courants de polarisation forts. Il est constitue d'un pont de resistance a basse temperature et d'un squid. Des mesures de bruit ont ete realisees sur des jonctions hybrides mesoscopiques supraconducteur/metal normal/supraconducteur (sns) possedant des interfaces ns tres transparentes. La reflexion d'andreev qui transforme le courant dissipatif dans n en supercourant dans s est responsable d'une augmentation du bruit dans ces structures. Dans le cas sns des charges multiples nettement superieures a 2e peuvent etre transmises. Dans notre gamme de temperature ces effets sont absents et on s'attend a un comportement plus proche des jonctions ns diffusives. Dans ce systeme des resultats theoriques recents predisent un doublement du bruit par rapport au cas normal, du fait du doublement de la charge dans le processus d'andreev. Nos mesures montrent bien une augmentation du bruit, qui reste inferieure au doublement. L'interaction electron-electron, qui est aussi responsable d'une augmentation du bruit par rapport au cas desordonne ne peut pas simplement expliquer nos donnees experimentales. Les resultats de bruit de grenaille sont completes par des mesures de bruit en 1/f interpretees dans le cadre de la theorie de faible localisation. La premiere partie de cet ouvrage tente de rassembler les principaux resultats recents qui consacrent le bruit comme un outil de premier ordre en physique mesoscopique.
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Reid, Steven John. "Education in post-Reformation Scotland : Andrew Melville and the University of St Andrews, 1560-1606 /." St Andrews, 2008. http://hdl.handle.net/10023/849.
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Pfeffer, Andreas Helmut. "Electronic properties of diffusive three-terminal Josephson junctions : a search for non-local quartets." Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENY068.
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Pendant ce travail de thèse, j'ai tout d'abord finalisé le développement d'un système expérimental unique dédié aux études de transport électronique de nanostructures multi-terminaux de faible impédance. Ce dispositif permet des mesures de conductance et de bruit à très basse température (30 mK), avec une résolution du pico-ampère en utilisant des SQUIDs comme amplificateurs de courant. Dans le chapitre 5, je fournis une description du fonctionnement de la mesure. De plus, je décris la calibration du dispositif et la manière de déduire des quantités physiques à partir des mesures.Au Chapitre 6, je décris des mesures de transport avec des jonctions diffusives à trois terminaux (trijonctions). Dans une géométrie, que l'on appelle T-shape, des électrodes supraconductrices d'Aluminium sont connectées entre-elles par une partie centrale métallique non-supraconductrice de Cuivre. Pour ces nanostructures, on observe des anomalies de conductance à basse tension qui n'ont jamais été observées expérimentalement. Ces anomalies de résistance/conductance ressemblant fortement à l'effet Josephson apparaissant lorsque deux des potentiels appliqués à la trijonction ont une somme nulle. Les anomalies sont présentes sur une large échelle de tension sans perte d'amplitude. De-même, elles montrent une grande robustesse en température. Des expériences sous champ magnétique appliqué montrent une forte suppression des anomalies pour un champ magnétique correspondant à flux magnétique dans la partie normale de l'ordre d'un quantum de flux. Ceci indique qu'un mécanisme cohérent de phase doit être à l'origine des anomalies. Dans la littérature, deux mécanismes sont proposés pour expliquer ces effets.Le premier, nommé "mode-locking", est un accrochage dynamique des courants Josephson ac, qui est induit par l'environnement expérimental (circuit). Cette situation a été étudiée dans les années soixante sur des microstructures Josephson couplées à base de liens faibles. Pour tester cette explication, nous avons mesuré un échantillon composé de deux jonctions Josephson spatialement séparées. Les anomalies n'apparaissent pas dans une telle géométrie, pas même avec une amplitude réduite. Ceci indique qu'une synchronisation par l'environnement expérimental ne peut pas être à l'origine des anomalies observées. Le deuxième mécanisme théorique évoqué est nommé "mode de quartet" et a été proposé récemment par Freyn et collaborateurs. L'une des électrodes supraconductrices distribue alors des doublets de paires de Cooper. Chacune de ces deux paires se scindent alors en deux quasiparticles se propageant chacune vers deux contacts supraconducteurs différents. Dans un tel mécanisme deux quasiparticules, issues de deux paires de Cooper différentes, arrivent sur chacun des deux contacts supraconducteurs. Lorsque les tensions appliquées entre le contact supraconducteurs émetteur et les deux autres contacts sont exactement opposés, les phases des fonctions d'ondes électroniques des quasiparticules arrivant sur un même contact supraconducteur sont telles que ces deux quasiparticules peuvent se recombiner pour former une paire de Cooper. Par ce mécanisme le doublet de paires de Copper émis se distribue de manière cohérente en deux paires de Cooper chacune dans un contact supraconducteur différent.Ce mécanisme est favorable, car il est robuste envers le désordre et peut ainsi exister sur une large échelle de tensions.Au cours de cette thèse, j'ai montré que ces anomalies sont effectivement présentes pour des tensions appliquées correspondant à des énergies bien supérieures à l'énergie de Thouless. A contrario, les effets cohérents responsables de l'effet Josephson ac doivent être fortement atténués sur cette même échelle d'énergie, ce qui rend peu probable le mécanisme de mode-lockingDuring this PhD, I have first finished the development of a unique experimental set-up, dedicated for studies of electronic transport of low impedance multi-terminal nanostructures. This set-up allows conductance and noise measurements at very low temperature (30 mK), with a resolution of a few pico-ampere by using SQUIDs as current amplifiers. In chapter 5, I give some explanation of the measurement working principle. Furthermore, I explain the calibration of the experimental set-up as well as how to extract physical quantities from the measurements.In chapter6, I explain transport measurements on diffusive tri-terminal junctions (tri-junction). In a T-shape called geometry, the superconducting Al-electrodes are connected via a common metallic, non-superconducting part of Copper. For these nanostructures, we observe features in the conductance at low voltage, which have been never observed yet experimentally. These features in conductance/resistance have a striking resemblance with a dc-Josephson effect, appearing when two applied potentials on the tri-junction compensate exactly each other.In literature, two mechanisms are proposed to explain this effect.The first mechanism, called "mode-locking", corresponds to a dynamic locking of ac-Josephson currents, which is induced by the experimental environment (circuit). This situation has been extensively studied in the 60's on coupled microstructures, based on weak links. In order to test this explanation, we have measured a junction, which is composed of two spatially separated Josephson junctions. The anomalies does not show up in such a geometry, even not with strongly reduced amplitude. This indicates, that synchronization via the experimental environment can't be the origin of the observed features. The second theoretical mechanism is named "quartet-mode" and has been recently proposed by Freyn and Co-workers. In this process, one superconducting electrode emits doublets of Cooper-pairs. Each of the two pairs splits into two quasi particles propagating toward different superconducting contacts. In such a mechanism, two quasi-particles originating of two different Cooper-pairs, arrive each in the two superconducting contacts. If the applied voltage between the emitting superconducting contact and the two other contacts is exactly opposite, the phase of the electronic wave functions of the arriving quasi-particles on the same superconducting contact are such, that these two quasi-particles can recombine by forming a Cooper-pair. Due to this mechanism, the emitted doublet of Cooper-pairs is coherently distributed as two Cooper-pairs, each of them in a different superconducting contact. This mechanism is favored, since it is robust with respect to disorder and can hence also exist over a large range of voltage. During this PhD, I have shown that these anomalies are indeed present for applied voltage corresponding to energies well above the Thouless energy. Argumentum a contrario, the coherent effects responsible for the ac Josephson-effect have to be strongly attenuated over the same range of energy, which makes low probable the effect of mode-locking
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Melina, Panaotović. "Техничко-стилске карактеристике драматургије Леонида Андрејева у периоду од 1905. до 1910. године." Phd thesis, Univerzitet u Novom Sadu, Filozofski fakultet u Novom Sadu, 2019. https://www.cris.uns.ac.rs/record.jsf?recordId=110601&source=NDLTD&language=en.
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Menjajući poetike, istražujući u oblasti forme, Leonid Andrejev u svom ranom dramskom stvaralaštvu ostaje veran svojoj inicijalnoj ideji: on promišlja ljudsku misao, njenu prirodu i njene moguće manifestacije, kao i moć i nemoć ljudske misli u svetu koji ga okružuje. U prvom periodu svog ranog stvaralaštva, definisanom kao realistički teatar, pisac sagledava tri različite manifestacije ljudske misli: nauku, religiju i revoluciju. U perodu potrage za novom dramskom formom, supstancionalnom teatru, misao dolazi u sukob sa supstancom i rađa se ideja da ljudska misao nije svemoguća, to jest da čovek ne može da živi vođen isključivo razumnim načelom. U trećem periodu svog ranog dramskog stvaralaštva, takozvanom melodramskom teatru, pisac se naizgled udaljava od svoje osnovne teme i afirmišući studentske uspomene, na biografskoj građi stvara dve psihološke melodrame. U sva tri navedena teatra, realističkom, supstancionalnom i melodramskom, pisac se služio bogatim aresenalom tehničko-stilskih sredstava. U radu se tumači upotreba hromatskog i muzičkog prosedea, priroda i funkcija didaskalija, portetna metaforičnost likova, kao i simbolični plan drama, te njihove tematske i idejne koncepcije. Zaključak je da je u potrazi za formom, u tim spontanim smenama poetika i bogatom korišćenju tehničko-stilskih sredstava (npr., montažnost dramskog teksta, kolektivni monolog, personalizacija i depersonalizacija aktera radnje; upotreba metafore, poređenja, metonimije, sinegdohe, sinestezije, groteske, lirskih paralelizama itd.), L. Andrejev ostao dosledan svojoj primarnoj ideji, promišljanju o moći i nemoći ljudske misli. Ta ista ideja ušla je u osnovu teatra panpsihe, koji je okarakterisao naredni plodan period ovog dramskog pisca.Although he was not consistent in his approach when poetics and the form were concerned, Leonid Andreyev never gave up on the initial idea in his early plays: in them he was deeply involved in consideration of human thought, its nature and its possible manifestations, as well as its power, or the lack of it. In the first phase of his early works, which is in this thesis termed a realist theater, the playwright takes into consideration three different manifestations of human thought: science, religion and revolution. During the period in which he was searching for a new form for his plays, the so-called substantialist theater, thought is confronted with substance, upon which a new idea emerges, that of powerlessness of human thought– human beings cannot live their lives based solely on the principle of rationality. In the third period of his early writing, the so-called melodramatic theater, the author seemingly deviates from main theme, and by returning to his university days, creates two autobiographical, psychological plays. In all three theaters, the realist, the substantialist and the melodramatic, the author uses a rich palette of technical and stylistic devices. This thesis offers analyses of chromatic and musical principles; the nature and function of stage directions; metaphorical nature of the characters; as well as the symbolism present in the plays. Searching for the form, through spontaneous shifts between different poetics and an array of technical and stylistic devices (such as editing of plays, collective monologue, personalization and depersonalization of the characters, the use of metaphor, simile, metonymy, synecdoche, synesthesia, grotesque, lyrical parallelisms), Leonid Andreyev remained loyal to his initial idea of pondering the power and weakness of human thought. This idea has become a constitutive part of pan-psyche theater that marked the next, rather fruitful period of this playwright.
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Peters, Brian. "Tuning the structural, magnetic and transport properties of full Heusler Co2FeAlxSi1-x compounds." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1408984221.
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Herrmann, Lorentz. "Carbon Nanotubes as Cooper Pair Beam Splitters." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2010. http://tel.archives-ouvertes.fr/tel-00528938.
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We report on conductance measurements in carbon nanotube based double quantum dots connected to two normal electrodes and a central superconducting finger. By operating our devices as Cooper pair beam splitters, we provide evidence for Crossed Andreev Reflection (CAR). We inject Cooper pairs in the superconducting electrode and measure the differential conductance at both left and right arm. The contacts split the device into two coupled quantum dots. Each of the quantum dots can be tuned by a lateral sidegate. If the two sidegates are tuned such that both quantum dots are at a transmission resonance, a considerable part of the injected Cooper pairs splits into different normal contacts. On the contrary, if only one of the two dots is at resonance, nearly all pairs tunnel to the same normal contact. By comparing different triple points in the double dot stability diagram, we demonstrate the contribution of split Cooper pairs to the total current. In this manner, we are able to extract a splitting efficiency of up to 50% in the resonant case. Carbon Nanotubes ensure ballistic transport and long spin-flip scattering lengths. Due to these properties they are promising candidates to investigate EPR-type correlations in solid state systems.
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Belu, Andreea Anamaria Verfasser], Andreas [Akademischer Betreuer] Offenhäuser, and Ulrich [Akademischer Betreuer] [Simon. "Neurons on 3D polymer nanostructures / Andreea Anamaria Belu ; Andreas Offenhäuser, Ulrich Simon." Aachen : Universitätsbibliothek der RWTH Aachen, 2017. http://d-nb.info/1169830706/34.
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Belu, Andreea Anamaria [Verfasser], Andreas Akademischer Betreuer] Offenhäuser, and Ulrich [Akademischer Betreuer] [Simon. "Neurons on 3D polymer nanostructures / Andreea Anamaria Belu ; Andreas Offenhäuser, Ulrich Simon." Aachen : Universitätsbibliothek der RWTH Aachen, 2017. http://d-nb.info/1169830706/34.
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Reid, Steven John. "Education in post-Reformation Scotland : Andrew Melville and the University of St Andrews, 1560-1606." Thesis, University of St Andrews, 2009. http://hdl.handle.net/10023/849.
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Andrew Melville (1545-1622) was the leader of the Presbyterian wing of the Scottish Kirk between 1574 and 1607, and he and his colleagues were a perpetual irritant to James VI and I in his attempts to establish a royal and Episcopal dominance over the Kirk. Yet much of Melville’s reputation has been based on the seventeenth-century Presbyterian historical narratives written by the likes of James Melville (Andrew’s nephew) and David Calderwood. These partisan accounts formed the basis of modern historiography in Thomas M’Crie’s monumentally influential Life of Andrew Melville. Modern historians broadly agree that Melville’s portrayal as a powerful and decisive church leader in these narratives is greatly exaggerated, and that he was at best an influential voice in the Kirk who was quickly marginalised by the adult James VI. However, only James Kirk has commented at any length on Melville’s other role in Jacobean Scotland—that of developing and reforming the Scottish universities. Melville revitalised the near-defunct Glasgow University between 1574 and 1580, and from 1580 to 1607 was principal of St Mary’s College, St Andrews, Scotland’s only divinity college. He was also rector of the University of St Andrews between 1590 and 1597. This thesis provides a detailed account of Melville’s personal role in the reform and expansion of the Scottish universities. This includes an analysis of his direct work at Glasgow, but focuses primarily on St Andrews, using the untapped archival sources held there and at the Scottish National Library and Archives to create a detailed picture of the development of the University after the Reformation. This thesis also evaluates the intellectual content of Melville’s reform programme, both as it developed during his time in Paris, Poitiers and Geneva, and as we see it in action in St Andrews.
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Lahanque, Reynald Borreli Guy. "Le réalisme socialiste en France 1934 - 1954 /." Nancy : Université Nancy 2, 2002. http://cyberdoc.univ-nancy2.fr/htdocs/docs_ouvert/doc115/2002NAN21025_1.pdf.
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