Orbital-Selective High-Temperature Cooper Pairing Developed in the Two-Dimensional Limit

TL;DR

This paper demonstrates orbital-selective high-temperature Cooper pairing in monolayer FeSe/SrTiO3, highlighting the role of electronic correlations and anisotropic pairing, which advances understanding of high-Tc superconductivity mechanisms.

Contribution

It provides experimental evidence of orbital-selective pairing in 1-UC FeSe and incorporates electronic correlations into theoretical models, revealing the importance of orbital differentiation.

Findings

Observation of highly anisotropic magnetic Cooper pairing in 1-UC FeSe

Theoretical modeling shows orbital selectivity is crucial for pairing mechanisms

Electronic correlations suppress the dxy orbital coherence, influencing pairing

Abstract

The orbital multiplicity in multiband superconductors yields orbital differentiation in normal-state properties, and can lead to orbital-selective spin-fluctuation Cooper pairing. This phenomenon has become increasingly pivotal in clarifying the pairing 'enigma' particularly for multiband high-temperature superconductors. In one-unit-cell (1-UC) FeSe/SrTiO3, the thinnest and highest-Tc member of iron-based superconductors, the standard electron-hole Fermi pocket nesting scenario is apparently not applicable since the Gamma-centered hole pockets are absent, so the actual pairing mechanism is the subject of intense debate. Here, by measuring high-resolution Bogoliubov quasiparticle interference, we report observations of highly anisotropic magnetic Cooper pairing in 1-UC FeSe. From a theoretical point of view, it is important to incorporate effects of electronic correlations within a spin-fluctuation pairing calculation, where the dxy orbital becomes coherence-suppressed. The resulting pairing gap is compatible with the experimental findings, which suggests that high-Tc Cooper pairing with orbital selectivity applies to 1-UC FeSe. Our findings imply the general existence of orbital selectivity in iron-based superconductors and the universal importance of electron correlations in high-Tc superconductors.