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arXiv · 2603.23657

A correlated insulator at the surface of the polar metal Ca$_3$Ru$_2$O$_7$

Daniel Halliday·Izidor Benedičič·Andela Zivanovic·Masahiro Naritsuka·Brendan Edwards·Tommaso Antonelli·Naoki Kikugawa·Dmitry A. Sokolov·Craig Polley·Andrew P. Mackenzie·Georg Held·Phil D. C. King·Peter Wahl
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Abstract

We investigate the electronic structure at the surface of the correlated oxide Ca$_3$Ru$_2$O$_7$, a low-symmetry ruthenate oxide which hosts an unconventional polar-metal phase. From a combination of angle-resolved photoemission spectroscopy and scanning tunneling spectroscopy measurements, we demonstrate that the surface hosts an insulating phase, a distinct departure from metallicity within the bulk. Utilizing quantitative low-energy electron diffraction in conjunction with electronic structure calculations, we show how this results from a combined surface structure relaxation and the impact of marked electronic correlations in this system. Our findings highlight the proximity of Ca$_3$Ru$_2$O$_7$ to an insulating metallic state, and illustrate how subtle structural distortions can control its emergent electronic phases.

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Daniel Halliday, Izidor Benedičič, Andela Zivanovic, Masahiro Naritsuka, Brendan Edwards, Tommaso Antonelli, Naoki Kikugawa, Dmitry A. Sokolov, Craig Polley, Andrew P. Mackenzie, Georg Held, Phil D. C. King, Peter Wahl. 2026-03-24. A correlated insulator at the surface of the polar metal Ca$_3$Ru$_2$O$_7$. https://arxiv.org/abs/2603.23657

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