# Unconventional superconductivity in the cage type compound Sc$_5$Rh$_6$Sn$_{18}$

## TL;DR

This study investigates the unconventional superconducting properties of Sc$_5$Rh$_6$Sn$_{18}$, revealing strong-coupling behavior and broken time-reversal symmetry, indicating a novel superconducting state in this cage compound.

## Contribution

It provides the first detailed experimental evidence of broken time-reversal symmetry in the superconducting state of Sc$_5$Rh$_6$Sn$_{18}$, a cage-type superconductor, using muon-spin relaxation measurements.

## Key findings

- Superconductivity is type-II with $T_c$ = 4.4 K.
- Sc$_5$Rh$_6$Sn$_{18}$ exhibits strong-coupling BCS behavior.
- Broken time-reversal symmetry observed below $T_c$.

## Abstract

We have examined the superconducting ground state properties of the caged type compound Sc$_5$Rh$_6$Sn$_{18}$ using magnetization, heat capacity, and muon-spin relaxation or rotation ($\mu$SR) measurements. Magnetization measurements indicate type-II superconductivity with an upper critical field $\mu_0H_{c2}(0)$ = 7.24 T. The zero-field cooled and field cooled susceptibility measurements unveil an onset of diamagnetic signal below $T_{\bf c}$ = 4.4 K. The interpretation of the heat capacity results below $T_{\bf c}$ using the $\alpha-$BCS model unveils the value of $\alpha$ = 2.65, which gives the dimensionless ratio 2$\Delta(0)/k_B T_{\bf c}$ = 5.3, intimating that Sc$_5$Rh$_6$Sn$_{18}$ is a strong-coupling BCS superconductor. The zero-field $\mu$SR measurements in the longitudinal geometry exhibit a signature of a spontaneous appearance of the internal magnetic field below the superconducting transition temperature, indicating that the superconducting state is characterized by the broken time-reversal symmetry (TRS). We have compared the results of broken TRS in Sc$_5$Rh$_6$Sn$_{18}$ with that observed in R$_5$Rh$_6$Sn$_{18}$ (R = Lu and Y).