Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session YY05: V: Complex Structured Materials, Including Graphene V |
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Sponsoring Units: DCMP Chair: Betul Pamuk, Cornell University Room: Virtual Room 5 |
Wednesday, March 22, 2023 10:00AM - 10:12AM |
YY05.00001: TBG as Topological Heavy Fermion II: Analytical approximations of the model parameters and enlarged continuous symmetries Maksim Borovkov, Dumitru Calugaru, Liam L.H. Lau, Zhida Song, Piers Coleman, Andrei B Bernevig The recently-introduced Topological Heavy-Fermion (THF) model [1] of twisted bilayer graphene (TBG) aims to reconcile the quantum-dot-like electronic structure of the latter observed by scanning tunneling microscopy, with its electron delocalization seen in transport measurements. The THF model achieves this by coupling localized fermions with anomalous conduction electrons. Originally, the parameters of the THF model were obtained numerically from the Bistritzer-Macdonald (BM) model of TBG [1]. In this work, we derive analytical expressions for the THF model parameters using tractable BM model approximations [2]. By numerically computing the THF model parameters across a vast experimentally-relevant parameter space, we show that the resulting approximations are remarkably good, i.e. within the 20% relative error for almost the entire parameter space. Finally, we derive enlarged continuous symmetries of the interaction Hamiltonian that arise in various limits of the model. |
Wednesday, March 22, 2023 10:12AM - 10:24AM |
YY05.00002: Heavy fermion representation for twisted bilayer graphene systems: a hybridized ZLL + OPW model Hao Shi, Xi Dai We construct a heavy fermion representation for twisted bilayer graphene (TBG) systems. Two local orbitals (per spin/valley) are analytically found, which are exactly the maximally localized zero modes of the continuum Hamiltonian near the AA-stacking center. They have similar properties to the Wannier functions found in a recent work, but also have a clear interpretation as the zeroth pseudo Landau levels (ZLL) of Dirac fermions under the uniform strain field created by twisting. The electronic states of TBG can be viewed as the hybridization between these ZLL orbitals and other itinerant states which can be obtained following the standard procedure of orthogonalized plane wave method. The "heavy fermion" model for TBG separates the strongly correlated components from the itinerant components and provides a solid base for the comprehensive understanding of the exotic physics in TBG. |
Wednesday, March 22, 2023 10:24AM - 10:36AM |
YY05.00003: Seaching for Moire flat bands in twisted bilayers of nodal materials Fan Cui, Congcong Le, Qiang Zhang, Xianxin Wu, Ching-Kai Chiu In twisted bilayer graphene (TBG), topological Dirac nodes can evolve to zero-energy flat bands as a critical playground for strongly correlated physics. Beyond TBG, considering different types of topological nodes in a variety of twisted bilayers and a direction-dependent interlayer coupling, we study the criteria for the emergence of flat bands in the Moire ´ Brillouin zone. Distinguished from TBG with two-fold degenerate flat bands, other bilayers with topological nodes can host two-fold degenerate as well as highly degenerate flat bands at different magic angles. The presence of multiple degeneracy flat bands in these systems may result in more rich correlation physics. |
Wednesday, March 22, 2023 10:36AM - 10:48AM |
YY05.00004: Topological invariant and domain connectivity in moiré materials Ikuma Tateishi, Motoaki Hirayama Moiré materials have become one of the most active fields in material science in recent years due to their high tunability and wide variety of quantum phases. Very recently, a moiré material in which topological insulator domains and normal insulator domains coexist in the moiré unit cell has been proposed. In this presentation, we show a correspondence between the topology of the domain structure in real space and a topological invariant of the moiré material at the charge neutral point. We also found a bulk-edge corresponding that is compatible with a continuous change of the truncation condition, which is specific in moiré materials. We demonstrate the correspondence in twisted Bernevig-Hughes-Zhang model by tuning its moiré periodic mass term. This result is expected to contribute to the design of moiré materials with more diverse quantum properties. |
Wednesday, March 22, 2023 10:48AM - 11:00AM |
YY05.00005: A First-principles Study of Structural and Electronic Properties of Moire Patterns of Twisted Bilayer Phosphorene Aswad Alhassan, Ming Yu The prudent assembly of monolayers of 2D vdW nanomaterials into multilayer heterostructures with moire potentials has opened a new area of research and methods to engineer multilayer systems with fascinating novel properties. Interests to explore the fundamental aspects of moire patterns of twisted bilayer phosphorene (TBP) has recently been on the rise. In our first-principles study, we explored the novel structural and electronic properties of some TBP by considering the anisotropic properties of phosphorene monolayer coupled with the layer-dependent electronic properties and twisting of one layer relative to the other. Preliminarily, our results show that the equilibrium interlayer distance, the cohesive energy, the electronic band structures, and the distribution of the valence band and conduction bands of TBP strongly depend on the stacking arrangement, the twist angles, and the local strains. We will discuss our findings in our presentation. |
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