Theoretical Solid State Physics

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Our group focuses on the study of strongly correlated many particle systems, where interactions play an important role. To do so we use and develop advanced theoretical tools, in particular tensor network and functional renormalization group methods.

The conductance through quantum point contacts (QPCs) is quantized in units of the conductance quantum. In addition to this well understood quantization, measured curves exhibit a shoulder at around 0.7 times the conductance quantum. In this regime, the electrical and thermal conductance show anomalous behavior in their dependence of parameters such as temperature, magnetic field or applied bias. These effects are collectively known as the 0.7-anomaly in QPCs. Their origin has been controversially discussed ever since they were first mentioned in 1996. Based on previous work in our group (Nature 501, 73–78, 2013), we show a possible path to unify different points of view on the origin of the 0.7-anomaly: Using a real-frequency Keldysh-fRG calculation, we find that throughout the subopen 0.7-anomaly region the barrier-induced peak of the local density of states is pinned to the chemical potential. Throughout the pinning region electrons traversing the QPC experience a spatially extended, slowly fluctuating spin background. This view bridges the gap between two previous, seemingly contradictory phenomenological descriptions, one based on localized but dynamic spins, the other on spatially extended but static spin structures.