$4\pi$ periodic Andreev bound states in a Dirac semimetal

TL;DR

This paper demonstrates the presence of 4π-periodic Andreev bound states in a Dirac semimetal-based Josephson junction, revealing topologically protected supercurrent contributions and tunable quantum states via magnetic fields.

Contribution

It reports the experimental observation of 4π-periodic Andreev bound states in a Dirac semimetal, highlighting their topological protection and tunability in Josephson junctions.

Findings

Significant 4π-periodic supercurrent contribution observed.

Topological protection enhances transmission resonances.

Magnetic field tuning switches junctions between 0 and π regimes.

Abstract

Electrons in a Dirac semimetals possess linear dispersion in all three spatial dimensions, and form part of a developing platform of novel quantum materials. Bi$_{1-x}$Sb$_x$ supports a three-dimensional Dirac cone at the Sb-induced band inversion point. Nanoscale phase-sensitive junction technology is used to induce superconductivity in this Dirac semimetal. Radio frequency irradiation experiments reveal a significant contribution of 4$\pi$-periodic Andreev bound states to the supercurrent in Nb-Bi$_{0.97}$Sb$_{0.03}$-Nb Josephson junctions. The conditions for a substantial $4\pi$ contribution to the supercurrent are favourable because of the Dirac cone's topological protection against backscattering, providing very broad transmission resonances. 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.