Muon spin rotation study of the ternary noncentrosymmetric superconductors Li$_2$Pd$_x$Pt$_{3-x}$B

TL;DR

This study uses muon-spin rotation and specific heat measurements to show that the entire family of Li$_2$Pd$_x$Pt$_{3-x}$B superconductors exhibits single-gap s-wave behavior regardless of doping level.

Contribution

It provides comprehensive experimental evidence that all compounds in the Li$_2$Pd$_x$Pt$_{3-x}$B family are single-gap s-wave superconductors across the doping range.

Findings

Muon-spin rotation relaxation rate is constant at low temperatures.

Magnetic penetration depth is field-independent in some compounds.

Specific heat shows exponential increase at low temperatures.

Abstract

We investigated the superconducting state of the noncentrosymmetric superconductors Li$_2$Pd$_x$Pt$_{3-x}$B with superconducting transition temperature $T_c$= 5.16(8) K ($x$=2.25), 3.56(8) K ($x=1.5$) and 2.60 K ($x=0$) by means of muon-spin rotation ($\mu$SR) and specific heat experiments. The $\mu$SR relaxation rate $\sigma_{sc}$ was found to be constant at low temperatures for all the compounds. Data taken at different magnetic fields show that the magnetic penetration depth $\lambda$ is field-independent for Li$_2$Pd$_{2.25}$Pt$_{0.75}$B and Li$_2$Pt$_{3}$B. The electronic contribution to the specific heat measured in Li$_2$Pd$_{1.5}$Pt$_{1.5}$B and Li$_2$Pt$_{3}$B increases exponentially at the lowest temperatures. These features suggest that the {\it whole family} of Li$_2$Pd$_x$Pt$_{3-x}$B are single-gap s-wave superconductors across the entire doping regime.