Antiperovskite superconductor LaPd$_{3}$P with noncentrosymmetric cubic structure

TL;DR

This study reports the discovery of a noncentrosymmetric cubic antiperovskite superconductor LaPd3P with a transition temperature of 0.28 K, combining experimental measurements and first-principles calculations to explore its electronic structure and superconducting properties.

Contribution

The paper introduces a new cubic noncentrosymmetric antiperovskite superconductor LaPd3P and analyzes its electronic structure and superconductivity, highlighting the effects of La deficiency and potential unconventional pairing.

Findings

LaPd3P is a noncentrosymmetric cubic superconductor with Tc = 0.28 K.

Theoretical and experimental DOS at the Fermi level differ, explained by La deficiency.

Observed Tc is lower than BCS estimate, suggesting possible unconventional superconductivity.

Abstract

Antiperovskites are a promising candidate structure for the exploration of new materials. We discovered an antiperovskite phosphide, LaPd$_{3}$P, following our recent synthesis of $A$Pd$_{3}$P ($A$ = Ca, Sr, Ba). While $A$Pd$_{3}$P and (Ca,Sr)Pd$_{3}$P were found to be tetragonal or orthorhombic systems, LaPd$_{3}$P is a new prototype cubic system ($a$ = 9.0317(1) A) with a noncentrosymmetric space group ($I-43m$). LaPd$_{3}$P exhibited superconductivity with a transition temperature ($T_\mathrm{c}$) of 0.28 K. The upper critical field, Debye temperature, and Sommerfeld constant ($\gamma$) were determined as 0.305(8) kOe, 267(1) K, 6.06(4) mJ mol-1 K-2 f.u.-1, respectively. We performed first-principles electronic band structure calculations for LaPd$_{3}$P and compared the theoretical and experimental results. The calculated Sommerfeld constant (2.24 mJ mol-1 K-2 f.u.-1) was much smaller than the experimental value of $\gamma$ because the Fermi energy ($E_\mathrm{F}$) was located slightly below the density of states (DOS) pseudogap. This difference was explained by the increase in the DOS at $E_\mathrm{F}$ due to the approximately 5 at.% La deficiency (hole doping) in the sample. The observed Tc value was much lower than that estimated using the Bardeen-Cooper-Schrieffer equation. To explain the discrepancy, we examined the possibility of an unconventional superconductivity in LaPd$_{3}$P arising from the lack of space inversion symmetry.