Evolution of superconductivity in Pr$_{1-x}$La$_{x}$Os$_{4}$Sb$_{12}$: Upper critical field measurements

TL;DR

This study investigates how the upper critical field in Pr$_{1-x}$La$_{x}$Os$_{4}$Sb$_{12}$ evolves with La substitution, revealing a crossover concentration affecting electron mass and superconducting properties.

Contribution

It provides new insights into the evolution of superconductivity and electron mass suppression in Pr$_{1-x}$La$_{x}$Os$_{4}$Sb$_{12}$ through specific heat measurements of $H_{c2}$.

Findings

Positive curvature in $H_{c2}$ vs. $T$ in samples with two superconducting transitions.

Identification of a crossover concentration $x_{cr} \\approx 0.25$ affecting electron mass.

Rapid suppression of effective electron mass below the crossover concentration.

Abstract

Measurements of the upper critical field $H_{c2}$ near $T_c$ of Pr$_{1- x}$La$_{x}$Os$_{4}$Sb$_{12}$ were performed by specific heat. A positive curvature in $H_{c2}$ versus $T$ was observed in samples and concentrations exhibiting two superconducting transitions. These results argue against this curvature being due to two-band superconductivity. The critical field slope - $dH_{c2}/dT$ suggests the existence of a crossover concentration $x_{cr} \approx 0.25$, below which there is a rapid suppression of effective electron mass with La-alloying. This crossover concentration was previously detected in the measurement of the discontinuity of $C/T$ at $T_c$.