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FRACTIONAL A. C. JOSEPHSON EFFECT AS EVIDENCE OF TOPOLOGICAL HINGE STATES INADIRAC SEMIMETAL NiTe2

Issue number 5 from 15.11.2024

We experimentally investigate Josephson current between two 5 µm spaced superconducting indium leads,coupled to a NiTe2single crystal flake, which is a type-II Dirac semimetal. Under microwave irradiation, wedemonstrate a. c. Josephson effect at millikelvin temperatures as a number of Shapiro steps. In addition to theinteger (n= 1,2,3,4, ...) steps, we observe fractional ones at half-integer values n= 1/2,3/2,5/2and 7/2,which corresponds to πperiodicity of current-phase relationship. In contrast to previous investigations, we donot observe 4πperiodicity (disappearance of the odd n= 1,3,5, ... Shapiro steps), while the latter is usuallyconsidered 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 NiTe2: since one canexclude bulk supercurrent in 5 µm long Josephson junctions, interference of the hinge modes is responsible forthe πperiodicity, while stable odd Shapiro steps reflect chiral character of the topological hinge states.

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