High-pressure effects on isotropic superconductivity in the iron-free layered pnictide superconductor BaPd2As2

TL;DR

This study reveals that BaPd2As2, a layered superconductor without iron, exhibits conventional isotropic superconductivity with Tc decreasing linearly under high pressure, accompanied by structural changes at specific pressures.

Contribution

It provides comprehensive experimental and theoretical analysis showing BaPd2As2's conventional, isotropic superconductivity and pressure-induced structural transitions.

Findings

Superconductivity in BaPd2As2 is isotropic and conventional.

Tc decreases linearly with increasing pressure.

Structural distortions occur at 12 GPa and 24.2 GPa.

Abstract

While the layered 122 iron arsenide superconductors are highly anisotropic, unconventional, and exhibit several forms of electronic orders that coexist or compete with superconductivity in different regions of their phase diagrams, we find in the absence of iron in the structure that the superconducting characteristics of the end member BaPd2As2 are surprisingly conventional. Here we report on complementary measurements of specific heat, magnetic susceptibility, resistivity measurements, Andreev spectroscopy, and synchrotron high pressure x-ray diffraction measurements supplemented with theoretical calculations for BaPd2As2. Its superconducting properties are completely isotropic as demonstrated by the critical fields, which do not depend on the direction of the applied field. Under the application of high pressure, Tc is linearly suppressed, which is the typical behavior of classical phonon-mediated superconductors with some additional effect of a pressure-induced decrease in the electronic density of states and the electron-phonon coupling parameters. Structural changes in the layered BaPd2As2 have been studied by means of angle-dispersive diffraction in a diamond-anvil cell. At 12 GPa and 24.2 GPa we observed pressure induced lattice distortions manifesting as the discontinuity and, hence discontinuity in the Birch-Murnaghan equation of state. The bulk modulus is B0=40(6) GPa below 12 GPa and B0=142(3) GPa below 27.2 GPa.