Manipulation & detection of electronic states of a few unit cell thick oxide films

报告人

Prof. Changyoung Kim 

Seoul National University

时间

2026年1月23日（星期五）下午3：00

地点

物质科学教研楼B902会议室

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.

报告摘要

2D systems can not only have physical properties distinct from those of 3D materials but also allow control/manipulation of their properties through stacking. For example, Mott insulating and superconducting states, unavailable in single layer graphene, are realized in twisted bilayer graphene. While these novel 2D systems are mostly obtained through exfoliation of van der Waals materials, a more conventional approach 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 including SrRuO₃, SrIrO₃ and (La,Sr)₂CuO₄ 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 E_F from the van Hov singularity [2]. We further controlled the strain and octahedron distortion of 1 uc films by using various substrates. 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].

Meanwhile, we were able to grow and measure the electronic structure of SrIrO₃ (SIO) as well as (La,Sr)₂CuO₄ (LSCO) films down to a single layer. 1 uc SIO films has the same crystal structure of that of 1 uc Sr₂IrO₄. Not surprisingly, it is found that SIO 1uc films have the electronic structure of Sr₂IrO₄: relativistic Mott insulating state with (short) AF order[5]. Meanwhile, a single layer of LSCO contains a single CuO₂ plane and gap measurements indicates superconductivity in a single CuO₂ plane[6].

参考文献

[1] Sohn et al., Nature Materials 20, 1643 (2021)

[2] Sohn et al., Nature Communications 12, 6171 (2021)

[3] Kim et al., Advanced Materials (2023)

[4] Ko et al., Nature Communications (2023)

[5] J. Y. Kim, in preparation

[6] Y. D. Kim, under review