Engineering Quantum Geometry at Oxide Interfaces

In oxide heterostructures, different materials are integrated into a single artificial crystal, resulting in a breaking of inversion symmetry across the heterointerfaces. A notable example is the interface between polar and nonpolar materials, where valence discontinuities lead to otherwise inaccessible charge and spin states. This approach paved the way for the discovery of numerous unconventional properties absent in the bulk constituents. However, control of the geometric structure of the electronic wave functions in correlated oxides remains an open challenge. Here, we create heterostructures consisting of ultrathin SrRuO3, an itinerant ferromagnet hosting momentum-space sources of Berry curvature, and LaAlO3, a polar wide-band-gap insulator. Transmission electron microscopy reveals an atomically sharp LaO/RuO2/SrO interface configuration, leading to excess charge being pinned near the LaAlO3/SrRuO3 interface. We demonstrate through magneto-optical characterization, theoretical calculations and transport measurements that the real-space charge reconstruction drives a reorganization of the topological charges in the band structure, thereby modifying the momentum-space Berry curvature in SrRuO3 [1]. We will also report the discovery of the first material system having both spin- and orbital-sourced Berry curvature: LaAlO3/SrTiO3 interfaces grown along the [111] direction. We independently detect these two sources and probe the Berry curvature associated to the spin quantum number through the measurements of an anomalous planar Hall effect. The observation of a nonlinear Hall effect with time-reversal symmetry signals large orbital-mediated Berry curvature dipoles. The coexistence of different forms of Berry curvature enables the combination of spintronic and optoelectronic functionalities in a single material [2,3].<br/><br/><b>References</b><br/>[1] T. van Thiel et al., <i>Physical Review Letters</i> <b>127</b>, 127202 (2021)<br/>[2] E. Lesne et al., <i>Nature Materials </i><b>22</b> (2023) 576<br/>[3] M.T. Mercaldo et al., <i>npj Quantum Materials </i><b>8 </b>(2023) 12