Large enhancement of superconducting transition temperature in single-element superconducting rhenium by shear strain.

Masaki Mito,Kazuma Nakamura,Hiroyuki Deguchi,Hideaki Matsui,Zenji Horita,Yoshifumi Ikoma,Kazuki Tsuruta,Hiroki Adachi,Hideaki Iwaoka,Naoki Shirakawa,Tohru Yamasaki,Tomiko Yamaguchi

doi:10.1038/srep36337

Abstract

Finding a physical approach for increasing the superconducting transition temperature (Tc) is a challenge in the field of material science. Shear strain effects on the superconductivity of rhenium were investigated using magnetic measurements, X-ray diffraction, transmission electron microscopy, and first-principles calculations. A large shear strain reduces the grain size and simultaneously expands the unit cells, resulting in an increase in Tc. Here we show that this shear strain approach is a new method for enhancing Tc and differs from that using hydrostatic strain. The enhancement of Tc is explained by an increase in net electron–electron coupling rather than a change in the density of states near the Fermi level. The shear strain effect in rhenium could be a successful example of manipulating Bardeen–Cooper–Schrieffer-type Cooper pairing, in which the unit cell volumes are indeed a key parameter.

Highlights

Finding a physical approach for increasing the superconducting transition temperature (Tc) is a challenge in the field of material science
The change in Tc under hydrostatic contraction, in which the strain tensor has only diagonal components, is not uniform; in simple metals such as Al, Zn, Ga, Cd, In, Sn, Hg, and Pb, Tc decreases under pressure, whereas in those such as V, Zr, and Tl, Tc increases under pressure[1,2]
When pure Re crystals with Tc of 1.69–1.70 K are placed under hydrostatic pressure, Tc decreases with a slope of dTc/dP ~ –2 × 10–2 K/GPa for P < 0.4 GPa, and the initial slope corresponds to approximately −1 × 10–2 K at a volume shrinkage of 0.1%6,7

Summary

Introduction

Finding a physical approach for increasing the superconducting transition temperature (Tc) is a challenge in the field of material science. The change in Tc under hydrostatic contraction, in which the strain tensor has only diagonal components, is not uniform; in simple metals such as Al, Zn, Ga, Cd, In, Sn, Hg, and Pb, Tc decreases under pressure, whereas in those such as V, Zr, and Tl, Tc increases under pressure[1,2]. The electron-lattice coupling parameter λ in equation (1) is expressed as λ =N(EF) /M , where is the average square phonon frequency. It is thought that the decrease in Tc with pressure in simple metals results from a weakening of λ due to the shift of the phonon spectrum to higher frequencies[1]. In this study of Re, we present a new approach for greatly increasing Tc, in which shear stress instead of hydrostatic pressure is a key parameter affecting the Tc value of superconductors

Methods

Results

Conclusion