A theoretical study of strongly interacting superfluids and superconductors

Sascha Hoinka

Gases of neutral atoms cooled to nanoKelvin temperatures exhibit remarkable behaviour such as superfluidity in which particles can flow indefinitely with zero friction. Superfluids made of fermionic particles are especially interesting as they occur in a variety of settings from neutron stars to superconductors; however, many of their physical properties are difficult to predict theoretically. This thesis presents experimental measurements of the universal contact parameter for a Fermi gas with strong interactions which characterizes the many-body properties of the system and secondly the spin susceptibility which describes how the system responds to magnetic fields. These results further our understandings of strongly interacting quantum systems.

C. Di Castro, Roberto Raimondi

Dominik Husmann, Shun Uchino, Sebastian Krinner +4 more

Point contacts provide simple connections between macroscopic particle reservoirs. In electric circuits, strong links between metals, semiconductors, or superconductors have applications for fundamental condensed-matter physics as well as quantum information processing. However, for complex, strongly correlated materials, links have been largely restricted to weak tunnel junctions. We studied resonantly interacting Fermi gases connected by a tunable, ballistic quantum point contact, finding a nonlinear current-bias relation. At low temperature, our observations agree quantitatively with a theoretical model in which the current originates from multiple Andreev reflections. In a wide contact geometry, the competition between superfluidity and thermally activated transport leads to a conductance minimum. Our system offers a controllable platform for the study of mesoscopic devices based on strongly interacting matter.

Dominik Husmann, Shun Uchino, Sebastian Krinner +4 more

Point contacts provide simple connections between macroscopic particle reservoirs. In electric circuits, strong links between metals, semiconductors, or superconductors have applications for fundamental condensed-matter physics as well as quantum information processing. However, for complex, strongly correlated materials, links have been largely restricted to weak tunnel junctions. We studied resonantly interacting Fermi gases connected by a tunable, ballistic quantum point contact, finding a nonlinear current-bias relation. At low temperature, our observations agree quantitatively with a theoretical model in which the current originates from multiple Andreev reflections. In a wide contact geometry, the competition between superfluidity and thermally activated transport leads to a conductance minimum. Our system offers a controllable platform for the study of mesoscopic devices based on strongly interacting matter.