Thursday, April 9 at 1:30 p.m. by videoconference
Julien Varignon
CRISMAT Laboratory, CNRS UMR 6508, ENSICAEN, Normandie University
Charge and orbital orders drive superconductivity in complex oxides
Abstract: Superconductivity, characterized by zero electrical resistance and expulsion of the magnetic field, remains limited by relatively modest critical temperatures Tc, reaching 135 K at best in cuprates at ambient pressure. In complex oxides, understanding the mechanisms by which Tc can be increased is a major challenge, particularly from the point of view of electronic and structural chemistry.
Oxides derived from Ruddlesden-Popper An+1BnO3n+1-type phases play a central role in this issue. In these systems, superconductivity frequently appears close to a transition between an insulating and a metallic phase. This transition is often associated with the disappearance of electronic orders such as charge orders (cationic dismutation) or orbitals, frequently linked to Jahn-Teller-type structural instabilities.
In this seminar, I show, using first-principles simulations based on density functional theory (DFT), that superconductivity emerges systematically in the vicinity of these ordered phases. Even if these orders disappear in the metallic phase, their fluctuations persist and generate sufficient electron-phonon coupling to initiate superconductivity.
These results thus suggest that ordered insulating and superconducting phases share a common origin1,2. Finally, I highlight that structural distortions of O₆ octahedral lattices, such as rotations, allow modulation of this electron-phonon coupling. This paves the way for an oxide structural engineering strategy to optimize Tc.
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1. J. Varignon, M. Bibes, and A. Zunger, Nat. Comm. 10, 1658 (2019)
2. A. A. Carrasco-Alvarez, S. Petit, W. Prellier, M. Bibes, and J. Varignon, Nat. Comm. 16, 1458 (2025)
https://univ-nantes-fr.zoom.us/j/88146334543?pwd=8GL4UQasDKOmY9g5XmabSbPm0nDZx7.1
Meeting ID: 881 4633 4543
Secret code: 468276
