By this author

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

Issue number 5 from 16.09.2025

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.

68 0

FERROMAGNETIC RESPONSE OF THIN NiI2 FLAKES UP TO ROOM TEMPERATURES

Issue number 4 from 16.09.2025

We investigate the magnetic response of thin NiI2 flakes for temperatures above 80 K. Since no magnetic ordering is expected for bulk NiI2, we observe clear paramagnetic response for massive NiI2 single crystals. In contrast, thin NiI2 flakes show well-defined ferromagnetic hysteresis loop within ±2 kOe field range. The value of the response does not scale with the sample mass, ferromagnetic hysteresis can be seen for any flake orientation in the external field, so it originates from the sample surface, possibly, due to the anisotropic exchange (Kitaev interaction). The observed ferromagnetism is weakly sensitive to temperature up to 300 K. If a flake is multiply exposed to air, ferromagnetic hysteresis is accompanied by the periodic modulation of the magnetization curves, which is usually a fingerprint of the multiferroic state. While NiI2 flakes can not be considered as multiferroics above 80 K, surface degradation due to the crystallohydrate formation decreases the symmetry of NiI2 surface, which produces the surface ferroelectric polarization in addition to the described above ferromagnetic one.

4 0