Place　:        Lecture Loom A632 and On Zoom (Hybrid)
Speaker　:   Prof. Mikito Koshino
Affiliation  :   Department of Physics, Osaka University
Title　:  　　Topological gap labeling in moire quasicrystals
Abstract：
 Twisted 2D materials, consisting of rotationally stacked layers, can generally beregarded as quasi-periodic systems (quasicrystals)in that the systems have multipleperiodicitiesincommensurate with each other.Here we present a novel approach to characterizing energy gaps in 2D quasi-periodicsystems using a set of second Chern numbers.Theses numbers correspond to quantized Hall conductivity in a 4D system,which isconnected tothe original 2D quasicrystal through a process of dimensional reduction.We apply the theory to hBN/graphene/hBN superlattice, where we find thattheelectronic spectrum exhibits fractal minigaps,and each of them is uniquely labeled bysix second Chern numbers.We also consider the bulk-edge correspondence in this system,and discover that thenumber of edge-states bands per unit length is determined by the second Chern numbersassociated with the gap.

[1] M. Koshino, H. Oka, Phys. Rev. Research 4, 013028(2022)

[2] H. Oka and M. Koshino, Phys. Rev. B 104, 035306 (2021)

 ------------------

Once you make a registration below, you will get the access information of Zoom by e-mail.

Contact : Takashi Oka（ext. 63280）