S. Hartl | Searcharxiv

arXiv2025

Magnetic field-bias current interplay in HgTe-based three-terminal Josephson junctions

We investigate HgTe/Nb-based three-terminal Josephson junctions in T-shaped and X-shaped geometries and their critical current contours (CCCs). By decomposing the CCCs into the contributions from individual junctions, we uncover how bias current and magnetic field jointly determine the collective Josephson behavior. A perpendicular magnetic field induces a tunable crossover between SQUID-like and Fraunhofer-like interference patterns, controlled by the applied bias. Moreover, magnetic flux produces pronounced deformations of the CCC, enabling symmetry control in the $(I_1,I_2)$ plane. Remarkably, we identify a regime of strongly enhanced Josephson diode efficiency, reaching values up to $\eta\approx 0.8$ at low bias and magnetic field. The experimental results are quantitatively reproduced by resistively shunted junction (RSJ) simulations, which capture the coupled dynamics of current and flux in these multi-terminal superconducting systems.

cond-mat.supr-con↗

arXiv2024

Quantum Hall effect and current distribution in the 3D topological insulator HgTe

We study the quantum Hall effect (QHE) in the three-dimensional topological insulator HgTe, which features topological Dirac-type surface states in a bulk gap opened by strain. Despite the co-existence of multiple carrier subsystems, the system exhibits perfectly quantized Hall plateaus at high magnetic fields. Here we study the system using three different experimental techniques: Transport experiments, capacitance measurements including the quantum capacitance, and current distribution measurements using electrostatically sensitive scanning probe microscopy. Our key finding is that at sufficiently high magnetic fields, the different electronic subsystems merge into one, and the current in a quantum Hall plateau is distributed across the entire width of the Hall bar device.

cond-mat.mes-hall↗