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Delocalization Transition of Disordered Axion Insulator
Zhi-Da Song, Biao Lian, Raquel Queiroz +3
The axion insulator is a higher-order topological insulator protected by inversion symmetry. We show that under quenched disorder respecting inversion symmetry {\it on average}, th…
Twisted bilayer graphene.VI. An Exact Diagonalization Study of Twisted Bilayer Graphene at Non-Zero Integer Fillings
Fang Xie, Aditya Cowsik, Zhi-Da Song +3
Using exact diagonalization, we study the projected Hamiltonian with Coulomb interaction in the 8 flat bands of first magic angle twisted bilayer graphene. Employing the U(4) (U(4)…
Twisted Bilayer Graphene V: Exact Analytic Many-Body Excitations in Twisted Bilayer Graphene Coulomb Hamiltonians: Charge Gap, Goldstone Modes and Absence of Cooper Pairing
B. Andrei Bernevig, Biao Lian, Aditya Cowsik +3
We find exact analytic expressions for the energies and wavefunctions of the charged and neutral excitations above the exact ground states (at rational filling per unit cell) of pr…
Twisted Bilayer Graphene IV. Exact Insulator Ground States and Phase Diagram
Biao Lian, Zhi-Da Song, Nicolas Regnault +3
We derive the exact insulator ground states of the projected Hamiltonian of magic-angle twisted bilayer graphene (TBG) flat bands with Coulomb interactions in various limits, and s…
Twisted bilayer graphene III. Interacting Hamiltonian and exact symmetries
B. Andrei Bernevig, Zhi-Da Song, Nicolas Regnault +1
We derive the explicit Hamiltonian of twisted bilayer graphene (TBG) with Coulomb interaction projected into the flat bands, and study the symmetries of the Hamiltonian. First, we…
Twisted bilayer graphene. II. Stable symmetry anomaly
Zhi-Da Song, Biao Lian, Nicolas Regnault +1
We show that the entire continuous model of twisted bilayer graphene (TBG) (and not just the two active bands) with particle-hole symmetry is anomalous and hence incompatible with…
Twisted bilayer graphene I. Matrix elements, approximations, perturbation theory and a 2-Band model
B. Andrei Bernevig, Zhi-Da Song, Nicolas Regnault +1
We investigate the Twisted Bilayer Graphene (TBG) model to obtain an analytic understanding of its energetics and wavefunctions needed for many-body calculations. We provide an app…
Concurrence of topological electrons and magnons in the Kagome ferromagnet CoCu3(OH)6Cl2
Zhuoran He, Aiyun Luo, Biao Lian +1
Spin and charge are two interrelated properties of electrons. However, most of previous works on topological matter study the electronic and magnonic excitations separately. In thi…
Strongly Correlated Chern Insulators in Magic-Angle Twisted Bilayer Graphene
Kevin P. Nuckolls, Myungchul Oh, Dillon Wong +5
Interactions among electrons and the topology of their energy bands can create novel quantum phases of matter. Most topological electronic phases appear in systems with weak electr…
Discovery of a quantum limit Chern magnet TbMn6Sn6
Jia-Xin Yin, Wenlong Ma, Tyler A. Cochran +23
The quantum level interplay between geometry, topology, and correlation is at the forefront of fundamental physics. Owing to the unusual lattice geometry and breaking of time-rever…
Emergent Symmetry and Valley Chern Insulator in Twisted Double-Bilayer Graphene
Yimeng Wang, G. William Burg, Biao Lian +4
Theoretical calculations show that twisted double bilayer graphene (TDBG) under a transverse electric field develops a valley Chern number 2 at charge neutrality. Using thermodynam…
Multiple Flat Bands and Topological Hofstadter Butterfly in Twisted Bilayer Graphene Close to the Second Magic Angle
Xiaobo Lu, Biao Lian, Gaurav Chaudhary +8
Moiré superlattices in two-dimensional (2D) van der Waals (vdW) heterostructures provide 20 an efficient way to engineer electron band properties. The recent discovery of exotic qu…