Abstract Prof. Kim received his Ph.D. in Applied Physics from Stanford University. After working at SSRL as a staff member, he took a faculty position at Yonsei University in the department of Physics. He moved to Seoul National University as a professor in the department of Physics and Astronomy as well as an associate director of the center for correlated electron systems.His expertise is in angle resolved photoelectron spectroscopy on correlated materials, including high temperature superconductors and topological materials. His recent research interest is focused on investigation of novel electronic phases, via in-situ ARPES, that can be realized in atomically thin films of correlated materials. In addition to the atomically thin film results, his notable accomplishments include observation of spin-charge separation and discovery of the role of orbital angular momentum in solids.32Professor, Department of Physics & Astronomy, Seoul National UniversityInvited Talk: S2-1Manipulation & Detection of Electronic States of Atomically Thin Filmsof Quantum MaterialsChangyoung Kim2D systems can not only have physical properties distinct from those of 3D materials but also allow control/manipulation of their properties. For example, Mott insulating and superconducting states, unavailable in a single layer graphene, are realized in twisted bilayer graphene systems. While these novel 2D systems are mostly obtained through exfoliation of van der Waals materials, a more conventional approach is to achieve it through thin film growth. In this presentation, I wish to introduce our research efforts to measure and manipulate electronic properties of a few unit-cell (uc) thick thin films by using thin film growth and in-situ angle resolved photoemission (ARPES). We started with ARPES on a few uc thick film of SrRuO3 (SRO), a prototypical metallic ferromagnet with spin-orbit coupling. It was found that nodal lines and quadratic band crossing points are generic features of ultrathin perovskite films. These symmetry-protected nodal lines and quadratic band crossing points are sources of Berry curvature that causes the sign changing anomalous Hall effects [1]. By using additional ‘conducting layer’, we were able to obtain the electronic structure of 1 uc thick SRO films. Our results show that 1 uc films are not insulators but remain metallic. Dosing experiments reveal that 1 uc films are correlated Hund metals caused by the high density of states near EF from the van Hov singularity [2]. We further controlled the strain and octahedron distortion of 1 uc films by using different substrates with various lattice constants. We demonstrate that the electronic state of 1 uc films can be manipulated from a good metal to a correlated Hund metal, and finally to a Mott insulator [3][4]. Our work on SRO was extended to SrIrO3 (SIO) and a cuprate superconductor (La,Sr)2CuO4 (LSCO). It is found that SIO 1uc films have the electronic structure of Sr2IrO4, relativistic Mott insulating state with (short) AF order, which is not surprising considering the similarity in their crystal structure. Meanwhile, 0.5 uc LSCO (a single CuO2 plane) shows a d-wave gap structure, strongly suggesting that superconductivity is retained even in a single CuO2 plane.[1] Sohn et al., NAT. MATER. 20, 1643-1649 (2021).[2] Sohn et al., Nat. Commun. 12, 6171 (2021). [3] Kim et al., Adv. Mater. (2023).[4] Ko et al., Nat. Commun. (2023).
元のページ ../index.html#32