Comparison of the pressure dependences of Tc in the trivalent d-electron superconductors

TL;DR

This study investigates how the superconducting transition temperature (Tc) in trivalent d-electron metals varies with pressure, revealing significant increases and phase transitions, and correlating Tc with electronic free volume.

Contribution

It provides extended high-pressure measurements of Tc for Sc and Lu, compares pressure dependences across several metals, and links Tc behavior to electronic structure factors.

Findings

Tc for Lu increases monotonically to 12.4 K at 174 GPa

Sc reaches 19.6 K at 107 GPa, then drops after a phase transition

Correlation between Tc and fractional free volume related to d electrons

Abstract

Whereas dhcp La superconducts at ambient pressure with Tc = 5 K, the other trivalent d-electron metals Sc, Y, and Lu only superconduct if high pressures are applied. Earlier measurements of the pressure dependence of Tc for Sc and Lu metal are here extended to much higher pressures. Whereas Tc for Lu increases monotonically with pressure to 12.4 K at 174 GPa (1.74 Mbar). Tc for Sc reaches 19.6 K at 107 GPa, the 2nd highest value observed for any elemental superconductor. At higher pressures a phase transition occurs whereupon Tc drops to 8.31 K at 111 GPa. The Tc(P) dependences for Sc and Lu are compared to those of Y and La. An interesting correlation is pointed out between the value of Tc and the fractional free volume available to the conduction electrons outside the ion cores, a quantity which is directly related to the number of d electrons in the conduction band.