Time reversal symmetry breaking and s-wave superconductivity in CaPd2Ge2: A $\mu$SR study

TL;DR

This study investigates the superconducting properties of CaPd2Ge2, revealing s-wave pairing and broken time-reversal symmetry through muon spin relaxation measurements, indicating unconventional superconductivity.

Contribution

First demonstration of time-reversal symmetry breaking in CaPd2Ge2 with s-wave superconductivity using $bc$SR techniques.

Findings

Superconducting transition temperature $T_c$ = 1.69 K.

Isotropic s-wave energy gap with $2Delta(0)/k_B T_c$ = 3.50.

Evidence of spontaneous magnetic fields indicating broken time-reversal symmetry.

Abstract

${\rm CaPd_2Ge_2}$ which crystallizes in ${\rm ThCr_2Si_2}$-type body-centered tetragonal structure exhibits superconductivity below the critical temperature $T_{\rm c} = 1.69$~K\@. We have investigated the superconducting gap structure and time reversal symmetry of the ground state in ${\rm CaPd_2Ge_2}$ by means of muon spin relaxation and rotation ($\mu$SR) measurements. Our analysis of $\mu$SR data collected in transverse magnetic field reveals BCS superconductivity with a single-band $s$-wave singlet pairing and an isotropic energy gap having the value $2\Delta(0)/k_{\rm B}T_{\rm c} = 3.50(1)$. Further, an increased relaxation rate in zero field $\mu$SR asymmetry spectra below $T_{\rm c} $ provides evidence for the presence of a spontaneous magnetic field in the superconducting state revealing that the time-reversal symmetry is broken in ${\rm CaPd_2Ge_2}$.