Enhancement of superconductivity on thin film of Sn under high pressure

TL;DR

This study demonstrates that combining thin film growth and high-pressure techniques can significantly enhance the superconducting transition temperature of Sn, reaching above 6 K and improving critical magnetic fields.

Contribution

The paper introduces a novel approach of applying high pressure to thin Sn films, achieving higher $T_{c}$ than previously reported, and explores the effects of grain refinement under pressure.

Findings

$T_{c}$ on thin films increased to above 6 K under high pressure.

The upper critical magnetic field was significantly enhanced.

Grain size refinement under pressure stabilizes higher $T_{c}$.

Abstract

We investigated the pressure effects of a superconductivity on thin films of Sn. Elemental superconductor Sn with a body-centered tetragonal structure, $\beta$-Sn, exhibits superconductivity below the superconducting transition temperature ($T_{\rm c}=3.72$ K) at ambient pressure. $T_{\rm c}$ of Sn increases with lowering dimension such as in thin film and nanowire growth, or by high-pressure application. For thin films, $T_{\rm c}$ exhibits a slight increase up to approximately 4 K compared to the bulk value, attributable to the crystalline size and lattice disorder. By applying pressure on a bulk Sn, $T_{\rm c}$ initially decreases from 3.72 K as the pressure increases. Further increasing pressure up to 10 GPa, $T_{\rm c}$ increases to 5.3 K with the structural transformation. However, the combination of these effects on thin films of Sn, namely, thin-film growth and pressure effects, remains underexplored. In this study, we combined film-growth and pressure-application techniques to further increase $T_{\rm c}$ using a diamond anvil cell with boron-doped diamond electrodes. The drop of the electrical resistance suggesting the onset of $T_{\rm c}$ on the thin film reached above 6 K in $\gamma$-Sn phase. Further, the upper critical magnetic field was drastically enhanced. Atomic force microscopy suggests that the refinement of the grain size of the thin film under the non-hydrostatic pressure conditions contributes to stabilizing the higher $T_{\rm c}$ of $\gamma$-Sn.