Dual Enhancement of Superconductivity in FeSe/SrTiO3 via Orbital and Correlation Synergy
arXiv:2607.27104 · doi:10.1073/pnas.2602209123
The paper shows that applying tensile strain to monolayer FeSe/SrTiO3 shifts the dz2 orbital toward the Fermi level, first enhancing electronic correlations and then hybridizing with the dxy band, which together increase the superconducting gap from 17.8 to 23.6 meV.
Abstract
In iron-based superconductors, the dz2 orbital band typically resides far below the Fermi level and has not been considered to participate in Cooper pairing. Here, using monolayer FeSe/SrTiO3 as a model system, we demonstrate that tip-induced tensile strain controllably shifts the dz2 band toward the Fermi level, driving a two-stage enhancement of superconductivity. In-plane lattice expansion first enhances electronic correlation, amplifying superconductivity in the initial stage. As strain further increases, the upward-shifted dz2 band hybridizes with the dxy band, reconstructing the pairing-active d-orbital bands and inducing a secondary, stronger gap enhancement. Collectively, these two stages enlarge the superconducting gap from 17.8 to 23.6 meV. Throughout this process, invariant Fermi wave vectors confirm that the enhancement originates from band renormalization and reconstruction rather than carrier doping. Our work establishes a route to tailor superconducting states via strain-activated electronic correlations and band engineering, and reveals a previously unrecognized orbital-selective pairing mechanism with broad implications for correlated multiband superconductors.
17 pages, 4 figures