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.

arXiv commentSome references have been added

References in corpus (25)

• Topological Insulators
• Topological insulators and superconductors
• Weyl and Dirac Semimetals in Three Dimensional Solids
• Classification of topological quantum matter with symmetries
• Colloquium: Topological Band Theory
• Electric Multipole Moments, Topological Multipole Moment Pumping, and Chiral Hinge States in Crystalline Insulators
• Induced Superconductivity in the Quantum Spin Hall Edge
• The Josephson critical current in a long mesoscopic S-N-S junction
• Edge-mode Superconductivity in a Two Dimensional Topological Insulator
• Strong and Fragile Topological Dirac Semimetals with Higher-Order Fermi Arcs
• 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
• Low-energy type-II Dirac fermions and spin-polarized topological surface states in transition-metal dichalcogenide NiTe${}_2$
• Fermi-crossing Type-II Dirac fermions and topological surface states in NiTe2
• π and 4π Josephson Effects Mediated by a Dirac Semimetal
• Fractional Order Shapiro Steps in Superconducting Nanowires
• Bulk and surface states carried supercurrent in ballistic Nb-Dirac semimetal Cd3As2 nanowire-Nb junctions
• Weak-link Josephson Junctions Made from Topological Crystalline Insulators
• Realization of a double-slit SQUID geometry by Fermi arc surface states in a WTe${}_2$ Weyl semimetal
• Multivalued current-phase relationship in a.c. Josephson effect for a three-dimensional Weyl semimetal WTe${}_2$
• Microwave studies of the fractional Josephson effect in HgTe-based Josephson junctions
• 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