Multiband Superconductivity of Heavy Electrons in TlNi2Se2 single crystal

TL;DR

This study reveals that TlNi2Se2 is a multiband superconductor with heavy electrons, fully gapped, and exhibits unique specific heat behaviors, expanding understanding of heavy electron superconductivity.

Contribution

It provides the first detailed analysis of the multiband heavy electron superconductivity in TlNi2Se2, including specific heat and critical field measurements.

Findings

TlNi2Se2 has a superconducting transition at 3.7 K.

The superconductor exhibits heavy electron effective mass (14-20 m_b).

The specific heat data fits a two-gap BCS model.

Abstract

Superconductivity has been first observed in TlNi$_2$Se$_2$ at T$_C$=3.7 K and appears to involve heavy electrons with an effective mass $m^*$=14$\sim$20 $m_b$, as inferred from the normal state electronic specific heat and the upper critical field, H_${C2}$(T). Although the zero-field electronic specific heat data, $C_{es}(T)$, in low temperatures (T < 1/4 T$_C$) can be fitted with a gap BCS model, indicating that TlNi$_2$Se$_2$ is a fully gapped superconductor, the two-gap BCS model presents the best fit to all the $C_{es}(T)$ data below $T_C$. It is also found that the electronic specific heat coefficient in the mixed state, $\gamma_N(H)$, exhibits a \textit{H}$^{1/2}$ behavior, which was also observed in some \textit{s}-wave superconductors, although once considered as a common feature of the \textit{d}-wave superconductors. Anyway, these results indicate that TlNi$_2$Se$_2$, as a non-magnetic analogue of TlFe$_x$Se$_2$ superconductor, is a multiband superconductor of heavy electron system.