[Paper Review] Superconductivity up to 17 K in the high-pressure rhombohedral-I phase of ReO3: a potential oxide analogy of hydride superconductors

P. F. Shan, T. L. Lu+11 more|arXiv (Cornell University)|Apr 18, 2023

Thermal Expansion and Ionic ConductivityMaterials Science3 citations

TL;DR

This study identifies superconductivity with a critical temperature (Tc) up to 17 K in the high-pressure rhombohedral-I phase of ReO3, stabilized under 12–39 GPa. The superconductivity arises from enhanced electron-phonon coupling due to a nearly close-packed oxygen sublattice, mirroring mechanisms in superhydride superconductors, establishing a rare oxide analog to light-element hydride superconductors.

ABSTRACT

As an A-site-vacant perovskite-type oxide, ReO3 undergoes sequential pressure-driven structural transitions associated with the rotation of ReO6 octahedra. The rhombohedral-I phase in the pressure range of 12-39 GPa is featured by a lattice of nearly close-packed oxygen layers intercalated with Re cations, in reminiscent of the recently discovered superhydride superconductors. A combined study of first-principles calculations and transport measurements under high pressures enabled us to discover superconductivity in the rhombohedral-I phase, and it shows a dome-shaped Tc(P) with a maximum Tc of 17 K at about 30 GPa. In addition to the enhanced density of states at Fermi level compared to that of the ambient phase, the vibrations of hexagonal-close-packed oxygen lattice significantly strengthen the electron-phonon coupling, which is responsible for observed superconductivity with a relatively high Tc. The present work thus establishes a rare case among oxide superconductors that the light-element oxygen lattice plays a crucial role in inducing superconductivity.

Motivation & Objective

• To investigate superconductivity in high-pressure phases of ReO3, an A-site-vacant perovskite oxide.
• To determine whether the rhombohedral-I phase of ReO3, featuring a close-packed oxygen lattice, exhibits superconducting behavior.
• To explore the role of electron-phonon coupling in inducing superconductivity in this oxide phase.
• To establish a connection between oxide systems and recently discovered hydride superconductors through structural and electronic similarities.

Proposed method

• High-pressure transport measurements were performed using a cubic anvil press to probe electrical resistivity and magnetic susceptibility up to 40 GPa.
• First-principles density functional theory (DFT) calculations were used to analyze electronic structure and phonon modes in the rhombohedral-I phase.
• The electron-phonon coupling strength was evaluated from calculated phonon spectra and density of states at the Fermi level.
• Structural transitions in ReO3 were tracked via pressure-dependent X-ray diffraction to identify the rhombohedral-I phase stability window.
• The critical temperature (Tc) was extracted from the onset of resistivity drop and diamagnetic shielding in magnetic measurements.
• A comparison was made between the electronic and vibrational properties of the rhombohedral-I phase and the ambient-pressure phase of ReO3.

Experimental results

Research questions

• RQ1 Does the rhombohedral-I phase of ReO3 exhibit superconductivity under high pressure, and if so, what is its critical temperature?
• RQ2 What is the origin of superconductivity in the rhombohedral-I phase of ReO3—specifically, is it driven by electron-phonon coupling?
• RQ3 How does the electronic structure, particularly the density of states at the Fermi level, differ in the rhombohedral-I phase compared to ambient-pressure ReO3?
• RQ4 To what extent does the close-packed oxygen sublattice in the rhombohedral-I phase mimic the behavior of hydrogen-rich lattices in superhydride superconductors?
• RQ5 Can ReO3 serve as a structural and electronic analog to superhydride superconductors in oxide systems?

Key findings

• Superconductivity was observed in the rhombohedral-I phase of ReO3 with a maximum critical temperature (Tc) of 17 K at approximately 30 GPa.
• The Tc exhibits a dome-shaped dependence on pressure, peaking at 30 GPa and suppressing above 39 GPa.
• The rhombohedral-I phase features a nearly close-packed oxygen lattice that enhances electron-phonon coupling, contributing to the observed superconductivity.
• First-principles calculations revealed a significant increase in the density of states at the Fermi level compared to the ambient-pressure phase.
• The vibrations of the hexagonal-close-packed oxygen lattice strongly mediate electron-phonon coupling, which is the primary mechanism for superconductivity.
• This work establishes ReO3 as a rare example of an oxide superconductor where the light-element oxygen sublattice plays a central role in enabling superconductivity, analogous to superhydride systems.