Evidence of s-wave pairing symmetry in layered superconductor Li$_{0.68}$NbO$_2$ from the specific heat measurement

TL;DR

This study provides evidence that the layered superconductor Li$_{0.68}$NbO$_2$ exhibits s-wave pairing symmetry, based on specific heat measurements and analysis consistent with BCS theory.

Contribution

It is the first to demonstrate s-wave pairing symmetry in Li$_{0.68}$NbO$_2$ through detailed specific heat analysis and resistivity measurements.

Findings

Superconducting transition at T_c ~ 5.0 K

Upper critical field H_{c2}(0) ~ 2.98 T

Electronic specific heat shows thermal activated behavior

Abstract

A high quality superconducting Li$_{0.68}$NbO$_2$ polycrystalline sample was synthesized by deintercalation of Li ions from Li$_{0.93}$NbO$_2$. The field dependent resistivity and specific heat were measured down to 0.5 K. The upper critical field $H_{c2} (T)$ is deduced from the resistivity data and $H_{c2}(0)$ is estimated to be $\sim 2.98$ T. A notable specific heat jump is observed at the superconducting transition temperature $T_c \sim 5.0$ K at zero field. Below $T_c$, the electronic specific heat shows a thermal activated behavior and agrees well with the theoretical result of the BCS s-wave superconductors. It indicates that the superconducting pairing in Li$_{0.68}$NbO$_2$ has s-wave symmetry.