Scientific Reports (Jan 2024)

Superconductivity of barium with highest transition temperatures in metallic materials at ambient pressure

  • Masaki Mito,
  • Hiroki Tsuji,
  • Takayuki Tajiri,
  • Kazuma Nakamura,
  • Yongpeng Tang,
  • Zenji Horita

DOI
https://doi.org/10.1038/s41598-023-50940-5
Journal volume & issue
Vol. 14, no. 1
pp. 1 – 9

Abstract

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Abstract Pressure-induced superconductivity often occurs following structural transition under hydrostatic pressure (P HP) but disappears after the pressure is released. In the alkali-earth metal barium, superconductivity appears after structural transformation from body-centered cubic structure to hexagonal-close-packed (hcp) structure at P HP = 5 GPa, and the superconducting transition temperature (T c) reaches a maximum of 5 K at P HP = 18 GPa. Furthermore, by stabilizing the low-temperature phase at P HP ~ 30 GPa, Tc reached a higher level of 8 K. Herein, we demonstrate a significantly higher T c superconductivity in Ba even at ambient pressure. This was made possible through severe plastic deformation of high-pressure torsion (HPT). In this HPT-processed Ba, we observed superconductivity at T c = 3 K and T c = 24 K in the quasi-stabilized hcp and orthorhombic structures, respectively. In particular, the latter T c represents the highest value achieved at ambient pressure among single-element superconducting metals, including intermetallics. The phenomenon is attributed to a strained high-pressure phase, stabilized by residual strains generated from lattice defects such as dislocations and grain boundaries. Significantly, the observed T c far exceeds predictions from DFT calculations under normal hydrostatic compressions. The study demonstrates the importance of utilizing high-pressure strained phases as quasi-stable superconducting states at ambient pressure.