Superconductivity and Disorder Effect in TlNi$_2$Se$_{2-x}$S$_x$ crystals

TL;DR

This study investigates how disorder affects superconductivity in TlNi$_2$Se$_{2-x}$S$_x$ crystals, revealing changes in critical temperature and volume fraction with substitution-induced disorder, providing insights into the superconducting mechanism.

Contribution

It presents the synthesis and characterization of TlNi$_2$Se$_{2-x}$S$_x$ crystals and explores the impact of disorder on their superconducting properties, a novel investigation in this Ni-chalcogenide system.

Findings

Superconductivity with $T_C$=2.3 K observed in TlNi$_2$S$_2$.

Superconducting properties vary with substitution-induced disorder.

Heavy electron behavior inferred from specific heat and critical field measurements.

Abstract

After our first discovery of superconductivity (SC) with $T_C$=3.7 K in TlNi$_2$Se$_2$, we grew successfully a series of TlNi$_2$Se$_{2-x}$S$_x$ (0.0 $\leq$ x $\leq$2.0) single crystals. The measurements of resistivity, susceptibility and specific heat were carried out. We found that SC with $T_C$=2.3 K also emerges in TlNi$_2$S$_2$ crystal, which appears to involve heavy electrons with an effective mass $m^*$=13$\sim$25 $m_b$, as inferred from the normal state electronic specific heat and the upper critical field, $H_{C2}(T)$. It was found that the $T_C$ and superconducting volume fraction in TlNi$_2$Se$_{2-x}$S$_x$ crystals changes with the disorder degree induced by the partial substitution of S for Se, which is characterized by the residual resistivity ratio (\textit{RRR}). The effect of the disorder on SC may provide some information for understanding the mechanism of SC in this new Ni-chalcogenide system.