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

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 $\le$ x $\le$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 $m^{\ast }$=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.

5 papers, 6 figures

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