Superconductivity in the presence of disorder in skutterudite-related La$_3$Co$_4$Sn$_{13}$ and La$_3$Ru$_4$Sn$_{13}$ compounds; electrical transport and magnetic studies

TL;DR

This study investigates superconductivity in La$_3$Co$_4$Sn$_{13}$ and La$_3$Ru$_4$Sn$_{13}$, revealing multiple superconducting phases, pressure effects, and the influence of disorder and chemical pressure on critical temperatures.

Contribution

It uncovers a second superconducting phase in La$_3$Ru$_4$Sn$_{13}$ and explores how disorder and chemical substitution affect superconducting properties.

Findings

La$_3$Ru$_4$Sn$_{13}$ exhibits a second superconducting phase at higher $T_c^{ ext{ iny$ullet$}}$

Critical temperatures decrease under pressure and magnetic field, with different rates for $T_c$ and $T_c^{ ext{ iny$ullet$}}$

Partial Co substitution increases $T_c^{ ext{ iny$ullet$}}$ above $T_c$ for $x<4$.

Abstract

La$_3$Co$_4$Sn$_{13}$ and La$_3$Ru$_4$Sn$_{13}$ were categorized as BCS superconductors. In a plot of the critical field $H_{c2}$ vs $T$, La$_3$Ru$_4$Sn$_{13}$ displays a second superconducting phase at the higher critical temperature $T_c^{\star}$, characteristic of inhomogeneous superconductors, while La$_3$Co$_4$Sn$_{13}$ shows bulk superconductivity below $T_c$. We observe a decrease in critical temperatures with external pressure and magnetic field for both compounds with $\frac{dT_c^{\star}}{dP} > \frac{dT_c}{dP}$. The pressure dependences of $T_c$ are interpreted according to the McMillan theory and understood to be a consequence of lattice stiffening. The investigation of the superconducting state of La$_3$Co$_x$Ru$_{4-x}$Sn$_{13}$ shows a $T_c^{\star}$ that is larger then $T_c$ for $x<4$. This unique and unexpected observation is discussed as a result of the local disorder and/or the effect of chemical pressure when Ru atoms are partially replaced by smaller Co atoms.