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TT: Fachverband Tiefe Temperaturen

TT 19: Topological Superconductors

TT 19.2: Vortrag

Mittwoch, 7. September 2022, 12:00–12:15, H23

Superconductivity in HgTe based quantum point contacts — •Johannes Baumann, Martin Stehno, Hartmut Buhmann, and Laurens Molenkamp — Institute for Topological Insulators and Physikalisches Institut, Experimentelle Physik 3, Universität Würzburg, 97074 Würzburg, Germany

Quantum point contacts have been suggested as tunable transmission elements in topological quantum circuits. We etched narrow constrictions into the weak links of topological Josephson junctions prepared from high-mobility, band-inverted HgTe quantum wells (2D topological insulator). In such devices, the conductance and supercurrent transmission decrease step-wise as we deplete the carriers in the constriction electrostatically with a gate. In the entire gating range, the supercurrent diffraction pattern in a perpendicular magnetic field exhibits a slow decay indicative of a small number of Andreev bound states funnelling through the constriction. Under microwave irradiation, odd Shapiro steps are suppressed in the current-voltage characteristic of the open constriction. This observation has been linked to the appearance of a 4pi-periodic contribution to the supercurrent of topological Josephson devices. Surprisingly, we recover all steps as we reduce the transmission to a small number of channels. We discuss possible origins of the effect and implications for topological quantum devices.