Superconductivity at 32 K in single crystal Rb$_{0.78}$Fe$_2$Se$_{1.78}$}

TL;DR

This study reports the successful growth of high-quality Rb$_{0.78}$Fe$_2$Se$_{1.78}$ single crystals exhibiting superconductivity at 32 K, with high upper critical fields and moderate anisotropy, contributing to understanding iron-based superconductors.

Contribution

The paper presents the synthesis and characterization of Rb$_{0.78}$Fe$_2$Se$_{1.78}$ single crystals with detailed superconducting properties, including critical temperature and magnetic field behavior, which is novel for this compound.

Findings

Superconducting transition at 32.1 K observed.

High upper critical field estimated at 180 T (in-plane).

Anisotropy ratio around 3.0.

Abstract

We successfully grew the high-quality single crystal of Rb$_{0.78}$Fe$_2$Se$_{1.78}$, which shows sharp superconducting transition in magnetic susceptibility and electrical resistivity. Resistivity measurements show the onset superconducting transition ($T_{\rm c}$) at 32.1 K and zero resistivity at 30 K. From the low-temperature iso-magnetic-field magnetoresistance, large upper critical field $H_{\rm c2}$(0) has been estimated as high as 180 T for in-plane field and 59 T for out-of-plane field. The anisotropy $H^{ab}_{\rm c2}$(0)/$H^{c}_{\rm c2}$(0) is around 3.0, right lying between those observed in K$_x$Fe$_2$Se$_2$ and Cs$_x$Fe$_2$Se$_2$.