Superconductivity in a new layered nickel-selenide CsNi2Se2

TL;DR

This paper reports the discovery of superconductivity at 2.7K in the layered nickel-selenide CsNi2Se2, characterized by specific heat and resistivity measurements, and explores its electronic properties through experimental and theoretical analysis.

Contribution

It is the first to identify superconductivity in CsNi2Se2 and analyzes its electronic structure, revealing a two-gap BCS behavior and low electron-electron correlation.

Findings

Superconducting transition temperature T_c = 2.7K.

Large Sommerfeld coefficient indicating high density of states.

Superconductivity explained by a two-gap BCS model.

Abstract

The physical properties of CsNi$_{2}$Se$_{2}$ were characterized by electrical resistivity, magnetization and specific heat measurements. We found that the stoichiometric CsNi$_{2}$Se$_{2}$ compound is a superconductor with a transition temperature \textit{T$_{c}$}=2.7K. A large Sommerfeld coefficient $\gamma$$_{n}$ ($\sim$77.90 mJ/mol$\cdot$K$^{-2}$), was obtained from the normal state electronic specific heat. However, the Kadowaki-Woods ratio of CsNi$_{2}$Se$_{2}$ was estimated to be about 0.041$\times$10$^{-5}$ $\mu\Omega$$\cdot$cm(mol$\cdot$K/mJ)$^{2}$, indicating the absence of strong electron-electron correlations in this compound. In the superconducting state, we found that the zero-field electronic specific heat data, $C_{es}(T)$ (0.5K $\leq$ T $<$ 2.6K), can be well fitted with a two-gap BCS model. The comparison with the results of the density functional theory (DFT) calculations suggested that the large $\gamma$$_{n}$ in the nickel-selenide superconductors may be related to the large Density of States (DOS) at the fermi surface.