Inferior interfacial superconductivity in 1 UC FeSe/SrVO${}_3$/SrTiO${}_3$ with screened interfacial electron-phonon coupling

Abstract

Monolayer FeSe/TiO${}_x$ and FeSe/FeO${}_x$ interfaces exhibit significant superconductivity enhancement compared to bulk FeSe, with interfacial electron-phonon coupling (EPC) playing a crucial role. However, the reduced dimensionality in monolayer FeSe, which may drive superconducting fluctuations, complicates the understanding of the enhancement mechanisms. Here we construct a new superconducting interface: monolayer FeSe/SrVO${}_3$/SrTiO${}_3$, in which the itinerant electrons of highly metallic SrVO${}_3$ films can screen all the high-energy Fuchs-Kliewer phonons, including those of SrTiO${}_3$, making it the first FeSe/oxide system with screened interfacial EPC while maintaining the monolayer FeSe thickness. Despite comparable doping levels, the heavily electron-doped monolayer FeSe/SrVO${}_3$ exhibits a lower pairing temperature ($T_{\mathrm{g}}$ $\sim$ 48 K) than FeSe/SrTiO${}_3$ and FeSe/LaFeO${}_3$. Our findings disentangle the contributions of interfacial EPC from dimensionality on enhancing $T_{\mathrm{g}}$ in FeSe/oxide interfaces, underscoring the importance of interfacial EPC in $T_{\mathrm{g}}$ enhancement. This FeSe/VO${}_x$ interface also provides a platform for studying the interfacial superconductivity.

Published in Nano Letters, 11 pages, 4 figures, 1 table