Prof. Jun-Hyung Cho [Department of Physics, Hanyang University, Korea]

Title: Competing charge density wave, magnetic order, and topological states in low-dimensional materials

Time: 3:00 - 4:00 PM, Tue., Jan.23, 2018

Place: Conference room 410, HPSTAR (Shanghai)

Host: Bin Chen

Abstract:

Low-dimensional electron systems exhibit many exotic quantum phases such as charge density wave (CDW), magnetic ordering, Mott state, or non-Fermi-liquid state. In this talk, I will present our recent first-principles density-functional theory (DFT) studies for the origin of the insulating phases of several 1D and 2D electronic systems [1-4]. First, I talk about indium nanowires on Si(111) which were initially proposed to have a metal-insulator (MI) transition in terms of the CDW mechanism with the Peierls dimerization caused by Fermi surface nesting. However, we reveal that the driving force of the CDW is attributed to the relaxation of the tensile strained In wires on Si(111) [1]. Our findings not only solve a long-standing puzzle about the driving force of the CDW formation in In/Si(111), but also have important implications for understanding the formation mechanism of CDW in quasi-1D electron systems [1-2]. Secondly, I discuss the competing charge density wave, antiferromagnetism, or topological states in the low-dimensional electron systems formed on GaN(101 ̅0), ZnO(101 ̅0), [3,4] and Bi(111) bilayer. Thirdly, the intriguing feature of a charge density wave (CDW) of transition metal dichalcogenide 1T-TaS2 is introduced, which involves the interplay of the charge, lattice, orbital, and spin degrees of freedom [5].

[1] H. J. Kim and J. H. Cho, Phys. Rev. Lett. 110, 116801 (2013)

[2] Zhang et al., Phys. Rev. Lett 113, 196802 (2014).

[3] S. W. Kim, Y. G. Kang, H. J. Kim and J. H. Cho, PRL 118, 239601 (2017).

[4] Y. G. Kang, S. W. Kim, and J. H. Cho, PRB 96, 235416 (2017).

[5] S. Yi, Z. Zhang, and J. H. Cho, Phys. Rev. Lett. (submitted).

Biography of the Speaker:





Prof. Jun-Hyung Cho graduated in 1983 from Han Yang University in physics. He then received a master from Seoul University and a PHD in in condensed matter physics in 1994 from POSTECH. He worked at the Fritz-Haber-Institut, Oak Ridge National Laboratory, National Renewable Energy Laboratory, and University of Texas at Austin as postdoctoral researchers. In 2003, he moved to Han Yang University as assistant professor in physics, and become associate and full professors in the same department. Since 2011, he has been spending 3 months each year at both the ICQD in USTC and the Zhengzhou University as a guest professor. He works in the first-principles electronic structure theory of a broad range of solid-state materials, especially in low-dimensional electron systems.