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 Y21: Moire Beyond Graphene III |
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Sponsoring Units: DCMP Chair: Thomas Heinzel, University of Dusseldorf Room: Room 213 |
Friday, March 10, 2023 8:00AM - 8:12AM |
Y21.00001: Possible Kondo Behaviors in Moiré Patterned 2M/2H Mixed Phase WS2 William R Scougale, Piumi I Samarawickrama, Joseph McBride, Wenyong Wang, Brian Leonard, John Ackerman, Jifa Tian, TeYu Chien Transition metal dichalcogenide (TMD) heterostructures have recently garnered excitement as platforms to study strongly correlated physics in low dimensional limits. With the wide variety of the polymorphic structures allowed in TMDs, these heterostructures provide a new route to engineer material properties. Here, we present scanning tunneling microscopy and spectroscopy (STM/S) observations on Moiré pattern regions of exfoliated mixed phase 2M/2H WS2 flakes. We examine the dI/dV spectra measured on a non-trivial Moiré pattern with features resembling the strongly correlated system. Kondo-like peak features are observed in the dI/dV spectra near zero bias and undergo a dramatic transition near 7.5 K, near the superconducting transition temperature of 2M WS2 (~8.5 K). In addition, stripe-like Moiré patterns are observed and are determined to be caused by twisting 2M WS2 bilayers. This type of Moiré pattern may provide a platform to observe Luttinger liquids in the one-dimensional strongly correlated regions. These observations show that the polymorphic heterostructures of TMDs can provide rich structural combinations to exhibit novel physics. |
Friday, March 10, 2023 8:12AM - 8:24AM |
Y21.00002: Itinerant magnetism in moiré heterobilayer Yubo Yang, Shiwei Zhang, Miguel A Morales We study the two-dimensional electron gas in an external moiré potential using quantum Monte Carlo (QMC) methods. This continuum model is believed to describe the low-energy electrons in certain transition metal dichalcogenide (TMD) heterobilayers such as WSe2/MoSe2 and WSe2/WS2 [1,2]. Using auxiliary-field quantum Monte Carlo (AFQMC), and diffusion Monte Carlo (DMC), we find significant modifications to the Hartree-Fock (HF) magnetic phase diagram. These include a larger stability region of the paramagnetic phase at small interaction and a closer competition between the dominant antiferromagnetic phase with the incipient ferromagnetic phase at large interaction. We characterize an itinerant magnetic state, which has noncollinear magnetic order. |
Friday, March 10, 2023 8:24AM - 8:36AM |
Y21.00003: Boundary Modes from Periodic Magnetic and Pseudomagnetic Fields in Graphene Phong T Vo, Eugene J Mele
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Friday, March 10, 2023 8:36AM - 8:48AM |
Y21.00004: Moiré Luttinger liquids in a high magnetic field Pengjie Wang, Guo Yu, Yanyu Jia, Ayelet J Uzan, Michael Onyszczak, Yue Tang, Tiancheng Song, Ratnadwip Singha, Xin Gui, Kenji Watanabe, Takashi Taniguchi, Robert Cava, Leslie M Schoop, Sanfeng Wu The observation of moiré Luttinger liquids in twisted bilayer WTe2 (tWTe2) has enabled a new experimental route to study coupled Luttinger liquids, where many theoretical predictions await experimental explorations. One of the interesting questions is how the electrons in the moiré Luttinger liquids would behave when they are subjected to a high magnetic field. In this talk, I will present our study of small angle tWTe2 up to 45 Tesla, and discuss possible mechanisms. |
Friday, March 10, 2023 8:48AM - 9:00AM |
Y21.00005: Indirect Moiré Superlattice Patterning of Monolayer Graphene Adam K Williams The electronic properties of a material can be manipulated by superimposing a spatially periodic superlattice potential. Initially explored in vertical semiconductor heterostructures and lithographically patterned two-dimensional electron gases, moiré patterning of superlattices at van der Waals (vdW) interfaces has emerged as a complementary route to engineered band structures. Although moiré patterns can reach smaller superlattice periodicities than practical with lithography, they can be non-uniform due to lattice reconstruction at the vdW interface. Furthermore, many of the moiré patterned superlattices explored thus far have hexagonal symmetry. Here we explore an indirect approach to moiré superlattice patterning by encapsulating monolayer graphene between dielectrics which would have a moiré pattern at their interface. The separation of the dielectric layers may mitigate moiré disorder arising from lattice reconstruction. Furthermore, indirect moiré patterns can be constructed by lattice mismatch or angular misalignment between dielectrics with a variety of point group symmetries. We comment on how this diversity of superlattice symmetries could pave the way to a variety of novel electronic phases. |
Friday, March 10, 2023 9:00AM - 9:12AM |
Y21.00006: Flat Bands and Moiré Potentials in Acoustic Twisted Bilayer Kagome Benjamin H November, Jeffery B Shi, Harris S Pirie, Stephen T Carr, Jennifer E Hoffman The discovery of vdW heterostructures has opened a vast parameter space of materials and twist geometries too large for direct exploration. Acoustic metamaterials offer a solution to efficiently prototype their quantum counterparts. For example, twisted bilayer graphene has already been translated into the field of acoustics [1]. Here we simulate the acoustic metamaterial analog of a twisted bilayer kagome lattice composed of interconnected air cavities, separated by a thin interlayer membrane. Using COMSOL Multiphysics, we accurately mimic the flattening of the Dirac cone expected from a tight-binding approach, as well as the reorganization of the single-layer kagome flat band modes to form a larger kagome lattice on the Moiré length scale. Additionally, the tunable density and thickness of the interlayer membrane allow us to increase the magic angle, resulting in smaller, more computationally-tractable supercells that permit the exploration of physics beyond the first magic angle. |
Friday, March 10, 2023 9:12AM - 9:24AM |
Y21.00007: Quantum Transport of Small-Angle Twisted Bilayer WTe2 at Ultralow Temperatures Guo Yu, Pengjie Wang, Yanyu Jia, Ayelet J Uzan, Michael Onyszczak, Tiancheng Song, Yue Tang, Xin Gui, Ratnadwip Singha, Kenji Watanabe, Takashi Taniguchi, Robert Cava, Leslie M Schoop, Sanfeng Wu Various intriguing quantum phases have been observed in monolayer WTe2, such as superconductivity, quantum spin Hall states and an excitonic insulating state. In small angle twist bilayer WTe2 (tWTe2), experiments show that an anisotropic 2D phase mimicking a Luttinger liquid emerges. Due to its strong electron correlations and unique Moiré superlattices, tWTe2 provides a new platform to study novel states beyond the Fermi liquid description, thus calling for more comprehensive studies at ultralow temperature. In this talk, I will present our recent efforts on transport studies of tWTe2 system at ultralow temperatures with various tuning knobs such as the twist angle. |
Friday, March 10, 2023 9:24AM - 9:36AM |
Y21.00008: Strain Induced Flat bands and fragile topology Xiaohan Wan, Chunli Huang, Siddhartha Sarkar, Kai Sun, Shizeng Lin Materials with flat electronic bands offer an important pathway towards the realization of strongly correlated phenomena such as the fractional quantum Hall effect and unconventional superconductivity. Recently, magic-angle twisted bilayer graphene has gained considerable attention because of the experimental observation of the unconventional superconductivity and orbital Chern insulators. In this talk, we study the flat bands and their topological properties in two dimensional materials under periodic strain. In monolayer graphene, strain acts as a gauge field but preserves time reversal symmetry. In a recent study, it was shown that monolayer graphene under periodic strain fields can support counter-propagating edge states on the same edge. We show that in other systems strain fields may not act as a gauge field but can still produce rich and unexpected phenomena, such as flat bands and fragile topology. |
Friday, March 10, 2023 9:36AM - 9:48AM |
Y21.00009: Gap labeling theorem for multilayer thin film heterostructures Mao Yoshii, Sota Kitamura, Takahiro Morimoto Quasiperiodic systems show a universal gap structure due to quasiperiodicity which is analogous to gap openings at the Brillouin zone boundary in periodic systems. The integrated density of states (IDoS) below those energy gaps are characterized by a few integers, which is known as the “gap labelling theorem” (GLT) for quasiperiodic systems. |
Friday, March 10, 2023 9:48AM - 10:00AM |
Y21.00010: Z2 nontrivial Moiré minibands and interaction-driven Quantum anomalous Hall insulators in Topological Insulator based Moiré Heterostructures Kai-Jie Yang, Chaoxing Liu, Peizhe Tang, Andrei B Bernevig, Zhen Bi, Zian Xu, Yanjie Feng, Frank Schindler, Yuanfeng Xu We studied the electronic band structure and its topological property of a topological insulator thin film under a Moir'e superlattice potential. The $mathbb Z_2$ non-trivial isolated mini-bands can generally appear for the low-energy Moir'e mini-band spectrum in the phase diagram when the Moir'e potential form a hexagonal lattice with six-fold rotation symmetry. The conduction (valence) mini-bands can be topologically non-trivial when the hexagonal lattice has two minima (maxima). For the nontrivial conduction mini-band case, we find both the two isolated lowest Kramers' pairs of conduction mini-bands have nontrivial $mathbb Z_2$ invariant when there is inversion, while only the isolated lowest Kramers' pair of mini-bands is topologically non-trivial when the inversion symmetry is broken. The Coulomb interaction can potentially drive the lowest conduction Kramers' mini-bands into the quantum anomalous Hall state at half-filling, which is further stablized in the inversion asymmetric case. We propose the atomic Sb layer on top of Sb$_2$Te$_3$ films to realize our model via the first principles calculations. |
Friday, March 10, 2023 10:00AM - 10:12AM |
Y21.00011: A multiscale low-energy continuum model for moiré phonons Ziyan Zhu, Jonathan Z Lu, Mattia Angeli, Daniel T Larson, Efthimios Kaxiras Multiscale continuum models have been widely applied to solving the electronic structure and understanding the lattice relaxation in twisted layered van der Waals heterostructures. However, a systematic study of the phonon properties of moiré materials is lacking due to the computational challenge of obtaining force fields accurately and the lack of periodicity. An accurate description of moiré phonons is critical to understanding the nature of observed superconductivity in moiré systems. In this work, we show that the same multiscale framework for electronic and mechanical properties can be used to study moiré phonons. We present a general continuum framework for low-energy moiré phonons in twisted bilayer heterostructures, based on the local configuration and first-principles density functional theory. Our model not only bypasses the need for a supercell approximation but is also computationally efficient while having the computational accuracy of first-principles calculations. |
Friday, March 10, 2023 10:12AM - 10:24AM |
Y21.00012: Probing the structure of low-energy moiré phonons in twisted bilayer heterostructures Jonathan Z Lu, Ziyan Zhu, Mattia Angeli, Daniel T Larson, Efthimios Kaxiras Theoretical modeling of moiré phonons is critical to understanding the origin of superconductivity and the Raman spectroscopy in twisted layered heterostructures. In this work, we develop a low-energy continuum model for phonons in twisted moiré bilayers, based on a local configuration-space approach that combines density functional theory (DFT). Based on this framework, we show how the low-energy phonon modes, including interlayer shearing and layer-breathing modes, vary with the twist angle. As the twist angle decreases, the frequencies of the low-energy modes are reordered and the atomic displacement fields corresponding to phonon eigenmodes break translational symmetry, developing periodicity on the moiré length scale. On three representatives crystals—bilayer graphene, bilayer molybdenum disulfide (MoS2), and molybdenum diselenide-tungsten diselenide (MoSe2/WSe2) —we describe these moiré phonons in terms of frequency, real-space geometry, and their magnitudes that correspond to their optical activities. |
Friday, March 10, 2023 10:24AM - 10:36AM |
Y21.00013: Probing correlated states with plasmonic origami Michal Papaj, Cyprian K Lewandowski Understanding the nature of strongly correlated states in flat-band materials (such as moiré heterostructures) is at the forefront of both experimental and theoretical pursuits. While optical techniques are often very successful in probing the properties of the underlying order, the very narrow bandwidth, which makes flat-band systems interesting, makes their optical investigation challenging. Here we propose to leverage strong light-matter coupling present in the flat-band systems to gain insight through dynamical dielectric response into the structure of the interacting state. We argue that as a result of the enlargement of the effective lattice of the system, conventional long-range plasmon becomes "folded" to yield a multiband plasmon spectrum. The structure of the plasmon spectrum is highly sensitive to the underlying order revealing valued insights such as the interaction-driven band gaps and the order periodicity. |
Friday, March 10, 2023 10:36AM - 10:48AM |
Y21.00014: Effective superlattice models for moiré electrons and excitons in twisted bilayers of anisotropic 2D semiconductors David A Ruiz-Tijerina, Isaac Soltero, Jonathan Guerrero-Sánchez, Francisco Mireles Twisted bilayer heterostructures of 2D materials forming moiré patterns have recently emerged as a family of versatile tabletop quantum simulators. Among the most recent phases of matter realized in moiré systems are Luttinger liquids[1] in bilayers of anisotropic 2D semiconductors, where the moiré pattern dramatically amplifies the anisotropy of the constituting layers, leading to dimensional reduction from 2D to 1D[2]. Theoretically, these systems are typically described by atomistic simulations[3-6], limited by computational cost to large twist angles. |
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