Dependence of the superconducting transition temperature of single- and polycrystalline MgB2 on hydrostatic pressure

TL;DR

This study investigates how hydrostatic pressure affects the superconducting transition temperature (Tc) of MgB2, showing a consistent decrease in Tc up to 32 GPa and highlighting the importance of pressure conditions.

Contribution

It provides the first comprehensive comparison of Tc dependence on hydrostatic pressure for single- and polycrystalline MgB2, clarifying the role of shear-stress effects.

Findings

Tc decreases from 39 K to 15 K under pressure

dTc/dP is approximately -1.11 K/GPa

Shear-stress effects influence reported pressure dependencies

Abstract

The dependence of Tc for MgB2 on purely hydrostatic or nearly hydrostatic pressure has been determined to 23 GPa for single-crystalline and to 32 GPa for polycrystalline samples, and found to be in good agreement. Tc decreases from 39 K at ambient pressure to 15 K at 32 GPa with an initial slope dTc/dP = -1.11(2) K/GPa. Evidence is presented that the differing values of dTc/dP reported in the literature result primarily from shear-stress effects in nonhydrostatic pressure media and not differences in the samples. Although comparison of these results with theory supports phonon-mediated superconductivity, a critical test of theory must await volume-dependent calculations based on the solution of the anisotropic Eliashberg equations.