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

Liu, Chaofei; Kreisel, Andreas; Zhong, Shan; Li, Yu; Andersen, Brian M; Hirschfeld, Peter; Wang, Jian · Nano Lett · 2022

basic_science · Level V

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Abstract

For multiband superconductors, the orbital multiplicity yields orbital differentiation in normal-state properties and can lead to orbital-selective spin-fluctuation Cooper pairing. The orbital-selective phenomenon has become increasingly pivotal in clarifying the pairing "enigma", particularly for multiband high-temperature superconductors. Meanwhile, in one-unit-cell (1-UC) FeSe/SrTiO<sub>3</sub>, since the standard electron-hole Fermi pocket nesting scenario is inapplicable, the actual pairing mechanism is subject to intense debate. Here, by measuring high-resolution Bogoliubov quasiparticle interference, we report observations of highly anisotropic magnetic Cooper pairing in 1-UC FeSe. Theoretically, it is important to incorporate orbitally selective effects of electronic correlations within a spin-fluctuation pairing calculation, where the d<sub><i>xy</i></sub> orbital becomes coherence-suppressed. The resulting pairing gap is compatible with the experimental findings, which suggests that high-<i>T</i><sub>c</sub> Cooper pairing with orbital selectivity applies to 2D-limit 1-UC FeSe. Our findings imply the general existence of orbital selectivity in iron-based superconductors and the universal significance of electron correlations in high-<i>T</i><sub>c</sub> superconductors.