Novel Superconducting SrSnP with Strong Sn-P Antibonding Interaction: Is the Sn Atom Single or Mixed Valent?

TL;DR

This study reports the discovery and characterization of superconducting SrSnP with a critical temperature of 2.3 K, revealing strong Sn-P interactions and an unusual Sn oxidation state through experimental and theoretical analyses.

Contribution

It provides the first detailed crystallographic, electronic, and superconducting characterization of SrSnP, highlighting its unique Sn oxidation state and strong covalent interactions as key to its superconductivity.

Findings

Superconductivity observed at Tc ≈ 2.3 K in SrSnP.

Strong Sn-P and Sr-P interactions stabilize the structure.

Sn atom likely has a single unusual oxidation state.

Abstract

The large single crystals of SrSnP were prepared using Sn self-flux method. The superconductivity in the tetragonal SrSnP is observed with the critical temperature of ~2.3 K. The results of a crystallographic analysis, superconducting characterization, and theoretical assessment of tetragonal SrSnP are presented. The SrSnP crystallizes in the CaGaN structure type with space group P4/nmm (S.G.129, Pearson symbol tP6) according to the single crystal X-ray diffraction characterization. A combination of magnetic susceptibility, resistivity, and heat capacity measurements confirms the bulk superconductivity with Tc = 2.3(1) K in SrSnP. According to the X-ray photoelectron spectroscopy (XPS) measurement, the assignments of Sr2+ and P3- are consistent with the chemical valence electron balance principles. Moreover, it is highly likely that Sn atom has only one unusual oxidation state. First-principles calculations indicate the bands around Fermi level are hybridized among Sr-d, Sn-p, and P-p orbitals. The strong Sn-P and Sr-P interactions pose as keys to stabilize the crystallographic structure and induce the superconductivity, respectively. The physics-based electronic and phononic calculations are consistent with the molecular viewpoint. After including the spin-orbit coupling (SOC) into the calculation, the band degeneracies at gamma-point in the first Brillouin zone (BZ) split into two bands, which yield to the van Hove singularities around Fermi level.