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Danilo Nikolic - ​ESR 7,  January 2018 - December 2020

University of Konstanz, Quantum Transport Group, Germany

Master thesis: "Josephson current and long - range spin - triplet proximity effect in a junction with inhomogeneous ferromagnet"
In our work, we have studied SFFS Josephson junction with two ferromagnets with noncollinear magnetizations perpendicular to the axis of symmetry. We have considered cases with different transparency of interfaces modeled by δ – function potentials. For strong exchange fields (h/EF = 0.1) and perpendicular magnetizations, we have found strong second harmonic in the Josephson currentphase relation which is the signature of long – range spin – triplet correlations. Nontransparent interfaces decrease the magnitude of the Josephson current because of a decreased probability of Andreev reflection. Nontransparency of F1/F2 interface results in large decrease of the Josephson current for perpendicular magnetizations. This shows that long – range spin – triplet correlations are generated only at F1/F2 interface. Department of Physics, University of Belgrade, Serbia

Personal Training Committee

Main Supervisor: Wolfgang Belzig, UKON

Co-supervisor: Denis Basko, CNRS

Mentor: Agnès Henri, EDP Sciences

Planned secondments

At AALTO (July/August 2018) for learning basics of the theory of refrigeration in mesoscopic devices,

At CNRS (Mid-October-Mid-December 2019)  to learn theoretical techniques of quantum tunneling in superconducting junctions,

At EDP (June/July 2020) to get trained in scientific writing and editing.

PhD project

Theory of time-dependent heat transport and detection of fluctuations

Objectives: I will investigate quantum thermodynamic transport realised in superconducting circuits. Pumping heat: I will first develop the concept of an energy pump in a mesoscopic superconductor-normal metal heterostructure. Using the phase sensitivity in Andreev interferometers, I will study the electronic and radiative transport of heat driven by a time-dependent flux. Using the Keldysh Green function method, I will describe the pumping of heat and charge from adiabatic to non-adiabatic driving in collaboration with ESR3. I will address the full transport statistics and relate it to fundamental thermodynamics concepts like entropy production. This discussion will have an impact on the experimental control of heat and charge transport in mesoscopic current standards as well as on tests of fundamental fluctuation relations in connection with the projects of ESR4 and ESR8. Measuring fluctuations of heat using superconducting threshold detectors: The detection of fluctuations in the quantum regime is a fundamental challenge. On the theoretical side one has to consider detection schemes in the weak, noninvasive limit to access correlations without disturbance. To develop a heat detection device, I will investigate a superconducting tunnel junction acting as a heat fluctuation filter. Embedded in an electromagnetic environment, radiative heat transfer will be taken into account. I will investigate the possibility of using superconducting single electron devices showing a pronounced even-odd effect as heat detector (relevant for ESRs 1, 2 and 6). The goal will be to propose a three-terminal device as realisation of a Maxwell demon, by operating an SSS or NSN SET far from equilibrium.

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