Fractional a.c. Josephson effect as evidence of topological hinge states in a Dirac semimetal NiTe₂
Kazmin D.Yu., Esin V.D., Timonina A.V., Koselnikov N.N., Deviatov E.V.

Received: April 25, 2024

DOI: 10.31857/S0044451024110117

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We experimentally investigate Josephson current between two 5 μ m spaced superconducting indium leads, coupled to a NiTe₂ 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=1,2,3,4,...) steps, we observe fractional ones at half-integer values n=1/2,3/2,5/2 and 7/2, which corresponds to π periodicity of current-phase relationship. In contrast to previous investigations, we do not observe 4π periodicity (disappearance of the odd n=1,3,5,... 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 NiTe₂: since one can exclude bulk supercurrent in 5 μ m long Josephson junctions, interference of the hinge modes is responsible for the π periodicity, while stable odd Shapiro steps reflect chiral character of the topological hinge states.