Non-magic angle twisted bilayer graphene: Double layer 2DEG with strong coupling
일 시 : 2021년 12월 02일 목요일 16:00
연 사 : 김 영 욱 교수 (대구경북과학기술원)
장 소 : 747호 & 온라인 (줌 회의ID: 811 0183 4598 , 암호: 783734)
HOST : 신 상 진 교수님
초 록
We report on the quantum Hall effect in two stacked graphene layers rotated by 2°. The tunneling strength among the layers can be varied from very weak to strong via the mechanism of magnetic breakdown when tuning the density. Odd-integer quantum Hall physics is not anticipated in the regime of suppressed tunneling for balanced layer densities, yet it is observed. We interpret this as a signature of Coulomb interaction induced interlayer coherence and Bose−Einstein condensation of excitons that form at half filling of each layer. A density imbalance gives rise to reentrant behavior due to a phase transition from the interlayer coherent state to incompressible behavior caused by simultaneous condensation of both layers in different quantum Hall states. With increasing overall density, magnetic breakdown gains the upper hand. As a consequence of the enhanced interlayer tunneling, the interlayer coherent state and the phase transition vanish. In addition, we will discuss recent observations of fractional quantum Hall effect and their phase transition at first excited Landau level in large twist angle device.