Unraveling Enhanced Superconductivity in Single-layer FeSe through Substrate Surface Terminations

Qiang Zou; Gi-Yeop Kim; Jong-Hoon Kang; Basu Dev Oli; Zhuozhi Ge; Michael Weinert; Subhasish Mandal; Chang-Beom Eom; Si-Young Choi; Lian Li

arXiv · 2502.16784

Unraveling Enhanced Superconductivity in Single-layer FeSe through Substrate Surface Terminations

Qiang Zou·Gi-Yeop Kim·Jong-Hoon Kang·Basu Dev Oli·Zhuozhi Ge·Michael Weinert·Subhasish Mandal·Chang-Beom Eom·Si-Young Choi·Lian Li

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Abstract

Single-layer FeSe films grown on (001) SrTiO3 substrates have shown a significant increase in superconducting transition temperature compared to bulk FeSe. Several mechanisms have been proposed to explain such enhancement, including electron doping, interfacial electron-phonon coupling, and strong electron correlations. To pinpoint the primary driver, we grew FeSe films on SrTiO3 substrates with coexisting TiO2 and SrO surface terminations. Scanning tunneling spectroscopy revealed a larger superconducting gap of 17 meV for FeSe on TiO2 compared to 11 meV on SrO. Tunneling spectroscopy also showed a larger work function on SrO, leading to reduced charge transfer, as confirmed by angle-resolved photoemission spectroscopy. Scanning transmission electron microscopy revealed distinctive interfacial atomic-scale structures, with the Se-Fe-Se tetrahedral angle changing from 109.9{\deg} on SrO to 105.1{\deg} on TiO2. Compared to dynamical mean field theory calculations, these results suggest optimal electron correlations in FeSe/TiO2 for enhancing high-temperature superconductivity.

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Qiang Zou, Gi-Yeop Kim, Jong-Hoon Kang, Basu Dev Oli, Zhuozhi Ge, Michael Weinert, Subhasish Mandal, Chang-Beom Eom, Si-Young Choi, Lian Li. 2025-02-24. Unraveling Enhanced Superconductivity in Single-layer FeSe through Substrate Surface Terminations. https://arxiv.org/abs/2502.16784

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