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Rebekka Garreis - ​ESR 8,  October 2018 - September 2021

ETH Zurich, Switzerland

Master thesis: "Magneto transport measurements in aluminium nano loop arrays"

Fluxoid quantisation in a superconducting ring yields a modulation of the magneto resistance in a magnetic field with a periodicity of h/2e. Amongst others, the coherence length of the superconductor determines these oscillations. Theory predicts a crossover to a h/e periodicity in the magneto resistance if the ring dimensions become smaller than the coherence length. The resistance of three different aluminium samples in a perpendicular magnetic field around the critical field were investigated. Two of the samples are designed as a double network consisting of decoupled small rectangular loops and coupled large loops, where the size of the small loops is in the order of 4.5 times the zero temperature coherence length. The third one is designed as a reference sample to better understand the signal of the first two samples and has no small loops at all. In all three samples Little-Parks oscillations are detected. Even though the crossover from h/2e to h/e could not be measured in any of the samples other interesting features can be seen for the different geometries. To better understand the results further measurements are needed. University of Konstanz, Germany. Supervisor E. Scheer, co-supervisor W. Belzig

Personal Training Committee

Main supervisor: Klaus Ensslin, ETH

Co-supervisor: Joonas Peltonen, AALTO

Mentor: Amaia Zurutuza, GRA SEMI

Planned secondments

At GRA SEMI, Spain (September 2019) to learn dry transfer and prepare and measure the highest mobility in single layer graphene

At AALTO, Finland (Summer 2021) to learn electron counting techniques with metallic structures

At NGU, Spain (Spring 2021) for training in molecular electronics

PhD Project

Mesoscopic thermodynamics with semiconductor quantum dots

Objectives: I will exploit the unique tuneability of quantum dots in order to investigate charge transport and charge fluctuations on the level of individual electrons. Recently it became possible to probe the Jarzynski relation (relating free energy differences and the irreversible work along an ensemble of trajectories) both for superconducting structures (AALTO) as well as for semiconductor quantum dots (ETH). The next step is to demonstrate that quantum dots can be driven out of equilibrium in order to measure transition of events that rarely occur in equilibrium because of occupation probabilities being so low. I will develop gate-pulsing and read-out schemes in order to extract tunnelling rates out of equilibrium, but also to determine entropy production and heat dissipation in contacts as well as in coupled quantum devices themselves. I will further attempt to realise a Maxwell’s demon situation by carefully tuning the input energies and measuring the dissipated energy when electrons escape to the leads. These experiments will be done in close collaboration with Early Stage Researcher 5 (AALTO, Finland, the pioneer in this field) and theoretically analysed in collaboration with Early Stage Researcher 7 (UKON, Germany).

Previous work in this domain could be mostly understood in terms of single-particle tunnelling rates. In this project, I will extend the experimental study in order to incorporate and understand effects such as level degeneracies (because of spin and orbit) as well as interaction effects that can modify single-particle energies and transition rates. This will be relevant for the understanding of thermodynamics of mesoscopic devices in general. In addition, I will explore fluctuations in coherently coupled quantum dots in order to understand quantum effects with this unique experimental approach.

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