The discovery of near-room-temperature superconductivity in superhydrides has stimulated profound research interest in exploring high-transition-temperature (high- T c ) superconductivity dominated by light elements. Following this rationale, oxygen, as another ubiquitous light element, theoretically possesses the potential to enhance electron-phonon coupling (EPC) and consequently achieve a high T c . However, in practical metal oxides, the strong electronegativity of oxygen atoms severely restricts their contribution to the density of states at the Fermi level ( N ( E F )). Consequently, the phonon vibration modes of the oxygen atomic lattice typically fail to induce strong EPC. Therefore, overcoming the constraints imposed by oxygen's strong electronegativity to discover superconductors that exhibit robust metal-oxygen covalent hybridization—and thereby activate a strong EPC mechanism dominated by the light-element oxygen lattice—remains a highly compelling frontier topic.
As a prototypical 5 d transition-metal oxide, ReO 3 features a unique A-site-vacancy perovskite structure. Due to the intense covalent hybridization between the Re-5 d and O-2 p orbitals, it exhibits exceptionally high electrical conductivity at ambient pressure, comparable to that of copper and silver. Driven by high pressure, its corner-sharing ReO 6 octahedra undergo continuous coupled rotations, accompanied by a series of structural phase transitions. Based on an in-depth investigation into the lattice evolution and correlated physical properties of this system under high pressure, a research team led by Prof. Jinguang Cheng from the Institute of Physics, Chinese Academy of Sciences / Beijing National Laboratory for Condensed Matter Physics recently made a breakthrough in the high-pressure superconductivity of ReO 3 . By integrating high-pressure synchrotron X-ray diffraction, electrical transport, and magnetic susceptibility measurements, and assisted by first-principles calculations, the team discovered a superconducting dome covering the pressure range of 12 to 39 GPa within the rhombohedral-I (R-I) high-pressure phase of ReO 3 . The experimentally measured maximum superconducting T c reached approximately 17.8 K, a discovery that sets a new record for the highest T c among all currently known 5 d transition-metal oxide superconductors. This achievement has been published in National Science Review under the title "Discovery of record-breaking high- T c superconductivity among 5 d transition-metal-oxides up to 17.8 K in ReO 3 ," with Associate Prof. Jianping Sun, Prof. Miao Liu, and Prof. Jinguang Cheng serving as co-corresponding authors.
The research team systematically elucidated the compressional evolution of the unique A-site-vacancy perovskite structure of ReO 3 under high pressure. At pressures exceeding 12 GPa, the ReO 6 octahedra exhibit coupled rotations along the <111> direction, progressively compressing the oxygen atomic lattice from its original Kagome configuration into a distorted triangular lattice (the R-I phase). Remarkably, as the pressure further increases beyond 30 GPa and the rotation angle reaches 30°, this lattice evolves into an almost perfect, ideal hexagonal close-packed (hcp) configuration. Such a highly densified packing arrangement of the light-element oxygen atomic layer is exceedingly rare in other oxide materials.
First-principles calculations uncovered the synergistic mechanism underpinning this record-breaking T c . On one hand, with escalating pressure, the strong hybridization between the Re-5 d and O-2 p orbitals doubles the N ( E F ) at 30 GPa compared to ambient pressure, vastly amplifying the contribution of oxygen's electronic orbitals to the N ( E F ). On the other hand, the phonon vibration modes associated with this distinctively dense oxygen atomic packing profoundly augment the EPC, driving the EPC constant λ from approximately 0.2 at ambient pressure to an impressive 0.9 at 34 GPa. Quantitative analysis indicates that under these extreme high-pressure conditions, the oxygen lattice itself accounts for over 50% of the total EPC contribution. It is precisely the synergistic interplay between the pressure-enhanced covalent hybridization and the oxygen-lattice-dominated EPC that actualizes such a high T c ; thus, the high-pressure R-I phase of ReO 3 can be conceptualized as an oxide analog of a light-element superconductor. This research not only substantiates the critical role of the light-element oxygen lattice in facilitating high- T c superconductivity, but also delineates a promising new paradigm for exploring novel superconducting materials via high-pressure synthesis or the precise regulation of metal oxides.
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Institute of Physics, Chinese Academy of Sciences (IOPCAS) is a leading research institution in China dedicated to condensed matter physics and related fields.
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