Pattern formation and orbital-selective metal skin in Ca₂RuO₄

Mario Cuoco

In this talk I will present the mechanisms for the occurrence of electronic phase reconstruction in quench dynamics and the surface doping insulator-to-metal (IMT) transitions in Ca₂RuO₄ (CRO). It is known that the control of Mott phase is intertwined with the spatial reorganization of the electronic states. Out-of-equilibrium driving forces typically lead to electronic patterns that are absent at equilibrium, whose nature is however often elusive. Here, I present how a nanoscale pattern formation can be realized in CRO. Applied gating can enable a spatial reconstruction of the insulating phase that, uniquely after switching off the electric field, exhibits nanoscale stripe domains [1]. I discuss how the electronic and structural reconstruction can be theoretically accounted by the quench of the orbital dynamics and noncentrosymmetric interface formation in CRO [1]. Then, I will consider the metallic state arising upon alkali-metal surface doping [2]. Photoemission spectroscopy demonstrates that CRO undergoes an IMT transition by surface doping developing a single band metal skin. Supported by a cluster model and cluster perturbation theory calculations, we demonstrate a novel type of skin metal-insulator transition induced by surface dopants that orbital-selectively hybridize with the bulk Mott state and in turn produce coherent in-gap states. 

[1] N. Gauquelin, F. Forte,…, A. Vecchione, J. Verbeeck, and M. Cuoco, Nano Lett. 23, 17, 7782 (2023).

[2] M. Horio, F. Forte, …, A. Vecchione, M. Cuoco, and J. Chang, arXiv:2310.13170 (to appear in Communication Physics)