Valence Bond Orders at Charge Neutrality in a Possible Two-Orbital Extended Hubbard Model for Twisted Bilayer Graphene

作     者：Yuan Da Liao Zi Yang Meng Xiao Yan Xu 

作者机构：Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences Beijing 100190 China School of Physical Sciences University of Chinese Academy of Sciences Beijing 100190 China Department of Physics and HKU-UCAS Joint Institute of Theoretical and Computational Physics The University of Hong Kong Pokfulam Road Hong Kong China Songshan Lake Materials Laboratory Dongguan Guangdong 523808 China CAS Center of Excellence in Topological Quantum Computation and School of Physical Sciences University of Chinese Academy of Sciences Beijing 100190 China Department of Physics Hong Kong University of Science and Technology Clear Water Bay Hong Kong China Department of Physics University of California at San Diego La Jolla California 92093 USA 

出 版 物：《Physical Review Letters》 (物理评论快报)

年 卷 期：2019年第123卷第15期

页      面：157601-157601页

核心收录：

学科分类：07[理学] 0702[理学-物理学] 

基　　金：Ministry of Science and Technology of the People's Republic of China, MOST National Key Research and Development Program of China, NKRDPC, (2016YFA0300502) National Key Research and Development Program of China, NKRDPC Chinese Academy of Sciences, CAS, (XDB28000000) Chinese Academy of Sciences, CAS Research Grants Council of Hong Kong Special Administrative Region of China, (17303019) National Natural Science Foundation of China, NSFC, (11574359) National Natural Science Foundation of China, NSFC 

主　　题：Dirac fermions Order parameters Quantum phase transitions Quantum spin Hall effect Bilayer films Dirac semimetal Graphene Strongly correlated systems Electron-correlation calculations Quantum Monte Carlo 

摘      要：An extended Hubbard model on a honeycomb lattice with two orbitals per site at charge neutrality is investigated with unbiased large-scale quantum Monte Carlo simulations. The Fermi velocity of the Dirac fermions is renormalized as the cluster charge interaction increases, until a mass term emerges and a quantum phase transition from Dirac semimetal to valence bond solid (VBS) insulator is established. The quantum critical point is discovered to belong to the 3D N=4 Gross-Neveu chiral XY universality with the critical exponents obtained at high precision. Further enhancement of the interaction drives the system into two different VBS phases, the properties and transition between them are also revealed. Since the model is related to magic-angle twisted bilayer graphene, our results may have relevance towards the symmetry breaking order at the charge neutrality point of the material, and associate the wide range of universal strange metal behavior around it with quantum critical fluctuations.