Electronically Driven Insulating to Conductive State in Correlated Oxides

On demand insulator-to-metal transition (IMT) offers a transformative pathway for next-generation brain-inspired computing [1,2]. Several correlated oxides exhibit electrically controlled IMT at remarkably low voltages [2]. Recent investigations suggest that electronic correlations, spin-orbit coupling, and structural distortions concurrently contribute to this electrically controlled non-standard Mott physics [3,4,5]. To decipher the leading mechanisms, it is essential to probe these degrees of freedom simultaneously. However, a suitable in situ bulk-sensitive probe with access to these degrees of freedom has been missing so far. Here, we developed a novel transport-RIXS setup and employed it to investigate the electrically controlled IMT in a prototypical correlated oxide candidate: Ca₂RuO₄ (CRO) [6]. Our findings reveal an energy-selective suppression of RIXS spectral weight across the electrically driven IMT, distinct from the trend observed for the thermally driven case, thus supporting the involvement of a new mechanism. Through dedicated RIXS cross-section calculations, we propose that electronic correlations are the leading players behind the electrically driven IMT, creating new states - charge defects - at the Fermi level. These newly created states enable the flow of current, leading to conduction without melting the underlying Mott insulating state. This work sheds light on the fundamental mechanism of current-driven IMT endemic to correlated oxides. The newly developed transport-RIXS setup opens the way to electrically driven quantum materials and artificial structures, promising advancements in microelectronics and quantum technology.<br/><br/>1. A. Mehonic et. al. Nature <b>604</b>, 255 (2022).<br/>2. Y. Zhou et. al., IEEE <b>103</b>, 8 (2015), A. Hoffman APL Mater<i>.</i> <b>10</b>, 070904 (2022).<br/>3. D. Sutter et al., Nat. Commun. 8, 15176 (2017).<br/>4. F. Nakamura et al., Sci. Rep. 3, 2536 (2013).<br/>5. C. Cirillo et al., Phys. Rev. B 100, 235142 (2019).<br/>6. M. Braden et al., Phys. Rev. B 58, 847 (1998).<br/><br/>Acknowledgements<br/>This work was supported by the US Department of Energy (DOE) Office of Science, Early Career Research Program. This research used beamline 2-ID of NSLS-II, a US DOE Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under contract no. DE-SC0012704.