“Electron quantum transport characteristics in twisted multi-layers of graphene”

Dr. Minsoo Kim
Department of Applied Physics, Kyung Hee University

Oct. 29 (Fri.), 02:30 PM
E6-2. 1st fl. #1323
https://kaist.zoom.us/j/85881284991
회의 ID: 858 8128 4991
암호: 884772

Abstract:
Twisted heterostructure of graphene multilayers offers a facile route for the study of topological properties and highly correlated phenomena, such as superconductivity, ferromagnetism, and correlated insulating states. At very small twist angles of ~0.1°, twisted bilayer graphene (TBG) exhibits a strain-accompanied lattice reconstruction resulting in submicron-size triangular domains with the standard, Bernal stacking. The domain boundary remains conductive due to a triangular network of topological one-dimensional states. First, I will present the electron quantum transport through this helical network and giant Aharonov-Bohm oscillations that reach in amplitude up to 50 % of resistivity and persist to temperatures above 100 K. On the other hand, the broken crystal symmetry in twisted monolayer-bilayer graphene (TMBG) allows higher control over the band structure. Here, I am going to show the electron quantum transport characteristics of correlated insulating states in TMBG at the twisted angle of ~1.2°. At half-filling, where two-electrons are filled per Moiré unit cell, the spin-polarized nature of the correlated insulating state lets observed ferromagnetism be isotropic. Electrically tunable metal-insulator quantum phase transition at half-filling also gives us a clue of the origin of correlated insulating state in TMBG. I will also discuss a critical-current behavior in non-linear current-voltage characteristics in graphene and its superlattices, resembling those of superconductors. The criticality develops upon the velocity of electron flow reaching the Fermi velocity, where the carrier distribution is shifted far from the equilibrium.