Combining thin film growth and spectroscopy to unveil novel states in oxide materials.

Electron correlation is responsible for numerous intriguing condensed matter phenomena, such as metal-insulator transitions, ferroelectricity, colossal magnetoresistance, 2D electron gases, and high-temperature superconductivity. Perovskite oxides serve as an attractive testbed for many of these phases, arising from the intricate interplay of spin, orbital, lattice, and charge degrees of freedom. One of the grand challenges in this field is understanding how strong quantum many-body interactions affect the electronic structure of these materials and ultimately lead to these exotic properties. In pursuit of this goal, researchers are increasingly focusing on the design and synthesis of artificial heterostructures, which offer new ways to tune material parameters and endow these systems with novel properties. I will present our recent studies of the alkaline earth stannates, particularly BaSnO3, which demonstrate light transparency and high electrical conductivity when doped. By combining thin film growth, angle-resolved photoemission spectroscopy, and ab initio calculations, we reveal the existence of a 2-dimensional metallic state at the SnO2-terminated surface of a 1% La-doped BaSnO3 thin film. This surface state is characterized by a distinct carrier density and a smaller effective mass compared to the corresponding bulk values. The small effective mass of the surface state, about 0.12me, indicates that BSO can be a crucial component in transition metal oxide heterostructures with significantly improved electrical conductivity.

If time permits, I will also present our recent work on synthesizing infinite-layer nickelates that exhibit unconventional superconductivity. Our angle-dependent anisotropic magnetoresistance measurements have provided crucial insights into the evolution of magnetic ordering from the parent compound phase to the superconducting state. The results suggest a similarity between superconducting nickelates and electron-doped cuprates.