# Seminar by Alexander Brinkman

Tuesday 2 October 2018 15:15 - 16:00

K-Space (Q179, Dept. Physics)

Published 2018-09-12 10:51 by Marica Kolobaric

**Observation of 4pi-periodic supercurrent in Bi1-xSbx Dirac semimetal based Josephson junctions**

Seminar Alexander Brinkman

MESA+ Institute for Nanotechnology, University of Twente, the Netherlands

Bi1-xSbx is classified as an accidental three-dimensional Dirac semimetal at a doping level of x = 3% for which a band inversion occurs. When a magnetic field is applied parallel to the current in Hall bar devices the degenerate Dirac cone splits into two Weyl cones and we observe a strong and negative magnetoresistance as an indication of the chiral anomaly.

The accidental three-dimensional Dirac semimetal is ideally suited for realizing Majorana bound states in superconducting hybrids since chirality prevents the 4pi-periodic current-phase relation from opening a gap at zero energy for Andreev bound states at perpendicular incidence. We observe a strong contribution of 4pi-periodic Majorana bound states to the supercurrent in Nb-Bi1-xSbx-Nb devices. The 4pi-modes are revealed by studying the junction under GHz microwave irradiation.

The conditions for a substantial 4pi-contribution to the supercurrent are favourable because of the Dirac cone's topological protection against backscattering, providing very broad transmission resonances and an enhanced lifetime of the 4pi-state due to local conservation of fermion parity. The large g-factor of the Zeeman effect from a magnetic field applied in the plane of the junction, allows tuning of the Josephson junctions from 0 to pi regimes.

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*The same morning Professor Brinkman will be the Faculty Opponent for Chunlin Yu's doctoral thesis: “Quantum Transport in Superconductor - Semiconductor Nanowire Hybrid Devices”.*