Superconductivity and the Effects of Pressure and Structure in Single Crystalline SrNi$_2$P$_2$

TL;DR

This study investigates the structural transitions and superconductivity in SrNi2P2 single crystals, revealing a conventional superconductor with pressure-dependent properties and suggesting reduced dimensionality as a factor for higher transition temperatures.

Contribution

It provides detailed experimental data on the structural and superconducting properties of SrNi2P2 under pressure, highlighting the persistence of superconductivity across phase transitions.

Findings

Superconductivity at 1.4 K in SrNi2P2

Structural transition at 325 K without magnetism

Superconductivity persists under pressure despite phase changes

Abstract

Heat capacity, magnetic susceptibility, NMR, and resistivity of SrNi2P2 single crystals are presented, illustrating a purely structural transition at 325 K with no magnetism. Bulk superconductivity is found at 1.4 K. The magnitude of the transition temperature T_c, fits to the heat capacity data, the small upper critical field $H_{c2}$ = 390 Oe, and Ginzburg-Landau parameter $\kappa$ = 2.1 suggests a conventional fully gapped superconductor. With applied pressure a second structural phase transition occurs which results in an 8% reduction in the c/a ratio of lattice parameters. We find that superconductivity persists into this high pressure phase, although the transition temperature is monotonically suppressed with increasing pressure. Comparison of these Ni-P data as well as layered Fe-As and Ni-As superconductor indicates that reduced dimensionality can be a mechanism for increasing the transition temperature.