Robust zero resistance in a superconducting high-entropy alloy at pressures up to 190 GPa

Abstract

SignificanceHigh-entropy alloys (HEAs) are made from multiple transition-metal elements in equimolar or near-equimolar ratios. The elements in HEAs arrange themselves randomly on the crystallographic positions of a simple lattice. In addition to their excellent mechanical properties, one HEA has been reported to display superconductivity. In this work, we report that the Ta–Nb–Hf–Zr–Ti high-entropy alloy superconductor exhibits extraordinarily robust zero-resistance superconductivity under pressure up to 190.6 GPa. This is an observation of the zero-resistance state of a superconductor all the way from 1-bar pressure to the pressure of the earth’s outer core without structure phase transition, making the superconducting HEA a promising candidate for new application under extreme condition.

Pressure effects on the electronic structure and superconductivity of(TaNb)0.67(HfZrTi)0.33high entropy alloy

“…An excellent additional test of our theoretical results would be a measurement of the electronic heat capacity under pressure, which would allow verification of the observed decrease in both N (E F ) and λ. Calculated pressure dependence of Tc of (TaNb)0.67(HfZrTi)0.33 for two constant values of µ * = 0.13 and µ * = 0.215, variable µ * (P ) (see, Fig 15) and compared to experiment [6]. The electron-phonon coupling constant λ is defined as:…”

“…Here, the same approach is applied to (TaNb) 0.67 (HfZrTi) 0.33 system to study evolution of superconducting properties under pressure. As far as the crystal structure is concerned, high pressure synchrotron X-ray diffraction measurements were performed in the pressure range from 0 to 96 GPa and it was shown that (TaNb) 0.67 (HfZrTi) 0.33 maintains the bcc structure, since no structural distortion was observed [6]. As there is no information on the crystal structure above this pressure we limit our studies to the pressure range from 0 to 100 GPa.…”

“…The lattice thermal expansion coefficient and unit cell volume have been measured experimentally and heat capacity was approximated by the Dulong-Petit law. The parameters B = 177 GPa and B = 2.87 were determined from the Birch-Murnaghan equation of state [6]. Values of those parameters are gathered in Table II, along with a data reported for similar alloys [59].…”

“…When the external pressure is applied, T c of (TaNb) 0.67 (HfZrTi) 0.33 increases up to about 10 K at around 50-60 GPa and then it remains practically constant up to about 100 GPa. After that, it slightly decreases to 9 K at 190 GPa [6]. In our work we investigate effects of pressure on the electronic structure and superconductivity in this disordered system to better understand microscopic mechanisms controlling these interesting T c (P ) characteristics.…”

“…As superconductivity in these materials is mediated by the electron-phonon interaction, recent discoveries also turned attention to the effect of extreme pressure on superconductivity in other materials, including bulk conventional superconductors. This includes recent high-pressure studies on superconductivity in Nb-Ti alloy [5] and (TaNb) 0.67 (HfZrTi) 0.33 high-entropy alloy (HEA) [6], on which we are focusing in the current work.…”