Observation of two-level critical-state in a van-der-Waals superconductor Pt(Bi$_{1-x}$Se$_x$)$_2$

TL;DR

This study investigates the magnetotransport properties of a doped van-der-Waals superconductor, revealing a two-level critical-state characterized by flux pinning effects through magnetoresistance measurements.

Contribution

It reports the observation of a two-level critical-state in Pt(Bi$_{1-x}$Se$_x$)$_2$, a novel superconducting van-der-Waals material, using systematic magnetotransport experiments.

Findings

Finite hysteresis in magnetoresistance indicates flux pinning.

Identification of a two-level critical-state in the superconductor.

Enhanced superconducting transition temperature with Se doping.

Abstract

Trigonal PtBi$_2$ is one of the attractive van-der-Waals materials because of the enhancement of its superconducting transition temperature $T_{\rm{c}}$ by doping chalcogen elements such as Se and Te. Recently, it has been reported that $T_{\rm{c}}$ of Pt(Bi$_{1-x}$Se$_x$)$_2$ is enhanced by a factor of 4, compared to the pristine PtBi$_2$, together with the polar-nonpolar structural phase transition. Thus, it is desirable to study electrical transport properties for this new superconducting compound. Here, we have performed magnetotransport measurements for Pt(Bi$_{1-x}$Se$_x$)$_2$ ($x$ = 0.06 and 0.08) thin-film devices and have observed a peculiar magnetoresistance where a finite hysteresis appears when the superconducting state is broken. By measuring the magnetoresistance systematically, we have attributed this magnetoresistance to the two-level critical-state where fluxons pinned in Pt(Bi$_{1-x}$Se$_x$)$_2$ play an important role.