2024-2025 Kavli Heising-Simons Junior Fellow
Faculty Advisor: Professor Feng Wang
Haleem Kim obtained his B.S. degree in physics from Seoul National University in South Korea. After finishing his military duty as a Korean citizen, he joined the research group of Professor Feng Wang as a Ph.D. student. His research work mainly focuses on experimental condensed matter physics and, in particular, using advanced spectroscopic techniques to study strongly correlated two-dimensional systems.
Optical spectroscopies play a crucial role in studying the magnetic properties of vdW heterostructure. Understanding spin statics and dynamics relies highly on optical techniques such as Magnetic Circular Dichroism spectroscopy and Magneto-Optical Kerr rotation. Haleem recently developed a customized Bluefors Dilution Refrigerator Measurement System for optical spectroscopy. The system can apply 12T, and the base temperature can reach 12mK. Absorption and magnetic circular dichroism measurements have been tested successfully on reference samples.
During his fellowship, using this state-of-the-art experimental capability, he will probe and understand the quantum spin liquid ground state at the twisted bilayer Moire platform. Theoretical study indicates that at specific electronic correlation strength windows U/t~9, gapped quantum spin-liquid phase can be realized near the mott-insulator to metal phase transition on the triangular Hubbard Model. The advantage of the 2D Moire system is the controllability of its Hamiltonian, such as bandwidth or on-site electron repulsion, in addition to the carrier density. It has been demonstrated that bandwidth can be tuned via a vertical electric field for twisted bilayer systems (WSe2/MoTe2, tWS2), leading to continuous metal-to-mott insulator transition. Although the system has been widely studied, the magneto-optical study is limited to a few K temperatures. Effective magnetic interaction (J) of the twisted system is the order of a few K. Thus, to understand the true magnetic ground state and excitation mode, it is essential to go below sub-K temperature. He expects to find a novel magnetic ground state near the Mott transition point at millikelvin temperature.