In this thesis we use Josephson and noise scanning tunneling microscopy for the study of conventional, unconventional (iron-based) and disordered superconductors. On the one hand, Josephson... Show moreIn this thesis we use Josephson and noise scanning tunneling microscopy for the study of conventional, unconventional (iron-based) and disordered superconductors. On the one hand, Josephson scanning tunneling microscopy allows us to directly visualize the superfluid density with high spatial resolution. On the other hand, noise scanning tunneling microscopy is employed for measuring the shot noise which detects the charge of the carriers forming a superconducting condensate. Show less
Triplet superconductivity refers to a condensate of equal-spin Cooper pairs (pairs of electrons with equal spin). While exceptionally rare in nature, triplet pairing of electrons can occur if... Show moreTriplet superconductivity refers to a condensate of equal-spin Cooper pairs (pairs of electrons with equal spin). While exceptionally rare in nature, triplet pairing of electrons can occur if either the temporal or spatial component of the superconducting wavefunction can be represented by an odd function. These are often referred to as odd-frequency and odd-parity triplets, respectively. We use hybrid magnetic devices to study the former, while the latter is investigated in mesoscopic structures of strontium ruthenate (Sr\tss{2}RuO\tss{4}). Show less
Combining ferromagnetism and superconductivity can lead to the development of a completely new generation of technology, with unique and powerful characteristics, called superconducting spintronics... Show moreCombining ferromagnetism and superconductivity can lead to the development of a completely new generation of technology, with unique and powerful characteristics, called superconducting spintronics. The task of developing this, however, is challenging because at the microscopic level the superconducting and ferromagnetic states are intrinsically incompatible. Under certain conditions, however, the conventional (singlet) superconducting state can be converted into the triplet one, with the spins of the electrons forming the Cooper pairs aligned parallel. The triplet state can coexist with ferromagnetism and is very interesting both for applications and from a fundamental point of view. In this thesis we study the electrical properties of small hybrid devices that mainly consist of superconducting and ferromagnetic layers. By measuring the electrical resistance of these devices as a function of parameters such as the temperature or the applied magnetic field, it is possible to indirectly infer important information about the state of the (super)conductivity in the different layers. We investigate different types of devices (multilayers, triplet spin valves and Josephson junctions), in order to address different aspects related to the generation of the triplet state, for a better and better control of the process. Show less
The thesis is devoted to applications of the anti de Sitter/Conformal field theory correspondence (AdS/CFT, also called holography) to various problems in different areas of theoretical physics. We... Show moreThe thesis is devoted to applications of the anti de Sitter/Conformal field theory correspondence (AdS/CFT, also called holography) to various problems in different areas of theoretical physics. We make use of AdS/CFT to get insights into the physics of superconductors, quark-gluon plasma, and to study properties of quantum field theories on non-causal backgrounds. In the first part of the thesis we construct a holographic model of a Bardeen-Cooper-Schrieffer-like superconductor and demonstrate that the Cooper instability of Fermi-liquids can be naturally described in holographic terms. We show that both the superconducting phase and the BEC/BCS crossover appear naturally. In the second part we address the problem of quark-gluon plasma formation in heavy ion collisions. We study the effect of finite chemical potential on this process and calculate physical properties of the resulting deconfined state. The third part is dedicated to study of evolution of a quantum system with violated causality. Using AdS/CFT we can map the complicated and poorly defined non-causal quantum dynamics onto a classical spacetime with closed timelike curves. Doing that we have derived the Green's function of the QFT and demonstrated that evolution of a quantum system can be consistent and non-pathological even at broken causality. Show less
Topological superconductors are a novel type of superconductors that carry Majorana particles at their boundary. These surface states are equal superpositions of electrons and holes, and hence are... Show moreTopological superconductors are a novel type of superconductors that carry Majorana particles at their boundary. These surface states are equal superpositions of electrons and holes, and hence are their own anti-particles. There has been a recent surge of theoretical and experimental effort to realize these special particles in the lab. While first observations support the theoretical predictions, fail-safe experimental evidence for Majoranas is still needed. Part of the challenge is that due to their vanishing charge they are not easily detected electrically. The topic of this thesis is the proposal and study of electrical signatures of Majoranas that are present in spite of their charge neutrality. By applying scattering and random matrix theory we first examine their generic properties. With the tool of numerical simulations we then put our predictions to test on realistic systems. Show less
We investigate the detection mechanism in superconducting single photon detectors via quantum detector tomography. We find that the detection event is caused by diffusion of quasiparticles from the... Show moreWe investigate the detection mechanism in superconducting single photon detectors via quantum detector tomography. We find that the detection event is caused by diffusion of quasiparticles from the absorption spot, combined with entrance of a vortex. Moreover, we investigate the behaviour of superconducting single photon detectors in an external magnetic field. Show less
A dynamic vortex line traces out a world sheet in spacetime. This thesis shows that the information of all its dynamic behaviour is completely contained in the world sheet. Furthermore a... Show moreA dynamic vortex line traces out a world sheet in spacetime. This thesis shows that the information of all its dynamic behaviour is completely contained in the world sheet. Furthermore a mathematical framework for order–disorder phase transitions in terms of the proliferation of such vortex world sheets is presented, leading to the prediction of quantized vortex lines of electric current in phase-disordered superconductors. Show less
