A Brinkman

Linnaeus Colloquium: Observation of 4pi-periodic supercurrent in Bi1-xSbx Dirac semimetal based Josephson junctions

Talk by Alexander Brinkman, 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. ​ 

​Coffee will be served before the talk at 15:00
Category Colloquium; Seminar
Location: Kollektorn, lecture room,
Starts: 18 October, 2018, 15:15
Ends: 18 October, 2018, 16:00

Published: Wed 15 Aug 2018. Modified: Wed 03 Oct 2018