Correlation-Induced Insulating Topological Phases at Charge Neutrality in Twisted Bilayer Graphene
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75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Engineering topics
Xu, Xiao Yan
Publications and source records attributed to Xu, Xiao Yan.
Identification of non-Fermi liquid fermionic self-energy from quantum Monte Carlo data
Quantum Monte Carlo (QMC) simulations of correlated electron systems provide unbiased information about system behavior at a quantum critical point (QCP) and can verify or disprove the existing theories of non-Fermi liquid (NFL) behavior at a QCP. However, simulations are carried out at a finite temperature, where quantum critical features are masked by finite-temperature effects. Here, we present a theoretical framework within which it is possible to separate thermal and quantum effects and extract the information about NFL physics at T = 0. We demonstrate our method for a specific example of 2D fermions near an Ising ferromagnetic QCP. We show that one can extract from QMC data the zero-temperature form of fermionic self-energy Σ(ω) even though the leading contribution to the self-energy comes from thermal effects. We find that the frequency dependence of Σ(ω) agrees well with the analytic form obtained within the Eliashberg theory of dynamical quantum criticality, and obeys ω 2/3 scaling at low frequencies. Our results open up an avenue for QMC studies of quantum critical metals.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Pair Density Wave in the Doped t - J Model with Ring Exchange on a Triangular Lattice
In our previous study, we found a quantum spin liquid phase with a spinon Fermi surface in the two dimensional spin-1/2 Heisenberg model with four-spin ring exchange on a triangular lattice. In this work we dope the spinon Fermi surface phase by studying the $t - J$ model with four-spin ring exchange. We perform density matrix renormalization group calculations on four-leg cylinders of a triangular lattice and find that the dominant pair correlation function is that of a pair density wave; i.e., it is oscillatory while decaying with distance with a power law. The doping dependence of the period is studied. This is the first example where a pair density wave is the dominant pairing in a generic strongly interacting system where the pair density wave cannot be explained as a composite order and no special symmetry is required.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Kekulé valence bond order in an extended Hubbard model on the honeycomb lattice with possible applications to twisted bilayer graphene
Using large-scale quantum Monte Carlo simulations, we exactly solve a model of fermions hopping on the honeycomb lattice with cluster charge interactions, which has been proposed as an effective model with possible application to twisted bilayer graphene near half-filling. Here, we find an interaction driven semimetal to insulator transition to an insulating phase consisting of a valence bond solid with Kekulé pattern. Finite size scaling reveals that the phase transition of the semimetal to Kekulé valence bond solid phase is continuous and belongs to chiral XY universality class.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Spinon Fermi Surface in a Cluster Mott Insulator Model on a Triangular Lattice and Possible Application to 1 T –TaS 2
1T-TaS 2 is a cluster Mott insulator on the triangular lattice with 13 Ta atoms forming a star of David cluster as the unit cell. We derive a two-dimensional XXZ spin-1/2 model with a four-spin ring exchange term to describe the effective low energy physics of a monolayer 1T-TaS 2 , where the effective spin-1/2 degrees of freedom arises from the Kramers degenerate spin-orbital states on each star of David. Here, a large scale density matrix renormalization group simulation is further performed on this effective model and we find a gapless spin liquid phase with a spinon Fermi surface at a moderate to large strength region of the four-spin ring exchange term. All peaks in the static spin structure factor are found to be located on the “2k F ” surface of a half-filled spinon on the triangular lattice. Experiments to detect the spinon Fermi surface phase in 1T-TaS 2 are discussed.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Symmetry-enforced self-learning Monte Carlo method applied to the Holstein model
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Chen, Chuang↗
Self-learning quantum Monte Carlo method in interacting fermion systems
We present the self-learning Monte Carlo method is a powerful general-purpose numerical method recently introduced to simulate many-body systems. In this work, we extend it to an interacting fermion quantum system in the framework of the widely used determinant quantum Monte Carlo. This method can generally reduce the computational complexity and moreover can greatly suppress the autocorrelation time near a critical point. This enables us to simulate an interacting fermion system on a $100 × 100$ lattice even at the critical point and obtain critical exponents with high precision.
36 MATERIALS SCIENCE↗