Regensburg 2022 – scientific programme

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MA: Fachverband Magnetismus

MA 31: Topological Insulators (joint session MA/KFM)

MA 31.4: Talk

Thursday, September 8, 2022, 16:00–16:15, H37

Probing the Superconductor / Quantum Anomalous Hall Interface — •Anjana Uday¹, Gertjan Lippertz^1,2, Andrea Bliesener¹, Alexey Taskin¹, and Yoichi Ando¹ — ¹University of Cologne, Cologne, Germany — ²KU Leuven, Leuven, Belgium

Recently, crossed Andreev conversion was reported in a hybrid quantum Hall (QH) / Superconductor (SC) system [1]. The evidence was based on the observation of a negative downstream resistance R_D in a three-terminal measurement of a Hall-bar device with respect to the grounded SC electrode. Similar experiments would be of great interest in the quantum anomalous Hall (QAH) / SC hybrid system, where superconductivity can be suppressed for control experiments by applying a magnetic field while keeping the 1D edge state unchanged. We fabricated Hall-bar devices from V-doped (Bi_xSb_1−x)₂Te₃ thin films contacted with Nb electrodes having various widths. We found a finite positive R_D which increases with decreasing the widths of the SC electrode due to the QAH breakdown mechanism [2]. We also found a clear increase in R_D upon killing the superconductivity with a magnetic field for Nb electrodes narrower than 200 nm; this can be attributed to either non-local Andreev reflections on top of the breakdown-induced finite R_D or local Andreev reflections on the 2D normal metal/SC interface, which can be created by the charge transfer from the Nb electrode to the gapped VBST surface state. In both cases our observation implies a high transparency of the SC/QAH interface.

[1] G.-H. Lee et al., Nat. Phys. 13, 693-698 (2017)

[2] G. Lippertz et al., arXiv:2108.02081 (2021)