Fractional ac Josephson effect as evidence of topological hinge states in a Dirac semimetal NiTe2

Abstract

We experimentally investigate Josephson current between two 5~$\mu$m spaced superconducting indium leads, coupled to a NiTe${}_2$ single crystal flake, which is a type-II Dirac semimetal. Under microwave irradiation, we demonstrate a.c. Josephson effect at millikelvin temperatures as a number of Shapiro steps. In addition to the integer ($n=1,2,3,\mathrm{4...}$) steps, we observe fractional ones at half-integer values $n=1/2,3/2,5/2$ and 7/2, which corresponds to $\pi$ periodicity of current-phase relationship. In contrast to previous investigations, we do not observe $4\pi$ periodicity (disappearance of the odd $n=1,3,\mathrm{5...}$ Shapiro steps), while the latter is usually considered as a fingerprint of helical surface states in Dirac semimetals and topological insulators. We argue, that our experiment confirms Josephson current through the topological hinge states in NiTe${}_2$: since one can exclude bulk supercurrent in 5~$\mu$m long Josephson junctions, interference of the hinge modes is responsible for the $\pi$ periodicity, while stable odd Shapiro steps reflect chiral character of the topological hinge states.

Some references have been added

References in corpus (9)

• Electric Multipole Moments, Topological Multipole Moment Pumping, and Chiral Hinge States in Crystalline Insulators
• Edge-mode Superconductivity in a Two Dimensional Topological Insulator
• Non-sinusoidal current-phase relationship in Josephson junctions from the 3D topological insulator HgTe
• Non-topological Origin of the Planar Hall Effect in Type-II Dirac Semimetal NiTe2
• Fractional Order Shapiro Steps in Superconducting Nanowires
• Interface superconductivity in a type-II Dirac semimetal NiTe${}_2$
• Josephson spin-valve realization in the magnetic nodal-line topological semimetal Fe${}_3$GeTe${}_2$
• Magnetic field filtering of the hinge supercurrent in unconventional metal NiTe${}_2$-based Josephson junctions
• Reentrant proximity-induced superconductivity for GeTe semimetal

Cited by in corpus (1)

• Diode effect in Shapiro steps in an asymmetric SQUID with a superconducting nanobridge