Multi-gap nodeless superconductivity in nickel chalcogenide TlNi2Se2

TL;DR

This study investigates the superconducting gap structure of TlNi2Se2, revealing evidence for multiple nodeless gaps through thermal conductivity measurements, which enhances understanding of nickel chalcogenide superconductors.

Contribution

It provides experimental evidence for multi-gap nodeless superconductivity in TlNi2Se2 using thermal conductivity data.

Findings

Residual thermal conductivity is very small, indicating no nodal quasiparticles.

Weak field dependence of residual thermal conductivity supports nodeless gaps.

Thermal conductivity exhibits an 'S'-shaped curve consistent with multiple gaps.

Abstract

Low-temperature thermal conductivity measurements were performed on single crystals of TlNi$_2$Se$_2$, a nickel-chalcogenide heavy-electron superconductor with $T_c$ $\simeq$ 3.7 K. In zero field, the residual electronic contribution at $T$ $\rightarrow$ 0 K ($\kappa_0/T$) was well separated from the total thermal conductivity, which is less than 0.45\% of its normal-state value. Such a tiny residual $\kappa_0/T$ is unlikely contributed by the nodal quasiparticles. Nodeless gap structure is supported by the very weak field dependence of $\kappa_0(H)/T$ in low magnetic fields. In the whole field range, $\kappa_0(H)/T$ exhibits an "$S$"-shape curve, as in the case of nickel pnictides BaNi$_2$As$_2$ and SrNi$_2$P$_2$. This common feature of nickel-based superconductors can be explained by multiple nodeless superconducting gaps.