Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Q55: Ferroelectricity and Magnetism in Twisted 2D materialsRecordings Available
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Chair: Jennifer Steele, Trinity University Room: Hyatt Regency Hotel -Adler |
Wednesday, March 16, 2022 3:00PM - 3:12PM |
Q55.00001: Band structure engineering of 2D materials using moiré ferroelectrics Kenji Yasuda, Xirui Wang, Kenji Watanabe, Takashi Taniguchi, Pablo Jarillo-Herrero Superlattice formation in real space develops a folded band structure in the reciprocal space in solids. Such superlattice has been achieved in various van der Waals heterostructures using a moiré pattern formed by stacking materials with different lattice constants, or by twisting two layers. The dramatic modification of the band structure has led to the discovery of various intriguing electronic phases. Here, we introduce a new approach for engineering the band structure using moiré ferroelectrics. Different from twisted bilayer graphene, twisted bilayer boron nitride is characterized by the local inversion symmetry breaking with ferroelectric polarization [1-3]. Thus, the moiré pattern is associated with the triangular network of alternating out-of-plane electric dipole moment. We study the proximity effect of the moiré ferroelectrics to the 2D materials to demonstrate its potential for band structure modification in arbitrary materials. |
Wednesday, March 16, 2022 3:12PM - 3:24PM |
Q55.00002: Polarization superlattices for controlling the electronic structure in graphene/h-BN multilayers Marta Brzezinska, Oleg V Yazyev Moiré superlattice systems based on twisted heterostructures of two-dimensional materials represent an emerging design principle for realizing novel physical phenomena. Motivated by the recent discovery of polarization superlattices in twisted multilayers of hexagonal boron nitride (h-BN) [1-3], we investigate the possibility of using these systems for controlling the properties of multilayer graphene by means of the polarization proximity effect. In particular, by using first-principles and tight-binding model calculations, we address the possibility of creating flat bands in the multilayer graphene subsystem. We further discuss the effects of lattice relaxation in graphene/h-BN heterostructures. |
Wednesday, March 16, 2022 3:24PM - 3:36PM |
Q55.00003: Electric field tunable layer polarization in moiré of moiré graphene-hBN heterostructures Ziyan Zhu, Stephen T Carr, Qiong Ma, Efthimios Kaxiras Ferroelectricity has been discovered in four-layer hexagonal Boron Nitride (hBN) — graphene heterostructures [1], but a microscopic theory of the system is still lacking. The system exhibits incommensurate moiré of moiré patterns due to the coexistence of the twist angle and the lattice constant mismatch. We developed a continuum model for electronic structures of the system, in which a Bernal-stacked graphene bilayer is encapsulated by top and bottom hBN layers with a twist angle. The model we developed is efficient compared to atomistic calculations, and we do not resort to a periodic approximation. We found that the low-energy bands exhibit layer polarization that is tunable via an external displacement field. |
Wednesday, March 16, 2022 3:36PM - 3:48PM |
Q55.00004: Tuning two-dimensional magnetism in twisted CrI3 double bilayers Hongchao Xie, Xiangpeng Luo, Gaihua Ye, Zhipeng Ye, Haiwen Ge, Suk Hyun Sung, Emily Rennich, Shaohua Yan, Yang Fu, Shangjie Tian, Hechang Lei, Robert Hovden, Kai Sun, Rui He, Liuyan Zhao Twisting two-dimensional (2D) atomic crystals can lead to a plethora of novel emergent electronic and phononic states. Such new states are absent in the constituent natural 2D crystals, which deems twisting as a new and efficient platform for realizing novel 2D phases. Recent discoveries of 2D magnetic atomic crystals open the door to design new magnetic properties via twisting, and indeed, there have been a few theoretical predictions on nontrivial magnetic phases developing in twisted 2D magnets. In this talk, I will show our recent efforts on tuning 2D magnetism by twisting two CrI3 bilayers and examining them with polarized magneto-Raman spectroscopy. While individual CrI3 bilayers and any homogeneous stacking of them should have a zero total magnetization, we report our finding that twisted CrI3 double bilayers at special twist angles around 1.1o realize an unexpected magnetic state with non-zero total magnetizations. This twist-induced net magnetization is believed to arise from competitions between coexisting ferromagnetic and antiferromagnetic interlayer exchange coupling within individual moiré supercells. |
Wednesday, March 16, 2022 3:48PM - 4:00PM |
Q55.00005: Non-twisted moiré matter: mesoscopic ordering in layered MnPS3 induced by electron beam irradiation Kevin M Roccapriore, Vinit Sharma, Swagata Acharya, Dimitar Pashov, Mikhail Katsnelson, David G Mandrus, Janice Musfeldt, Sergei V Kalinin, Mark P Oxley, Nan Huang, Timothy Taylor Shaping matter to provide a desired functionality has been a dream of the condensed matter, physics, and materials science communities. Recently, the field of twistronics has emerged as a route to achieving a tremendous variety of exotic electronic, optical, and quantum properties by creating periodically ordered structures in 2D materials. Until now, the only mechanism to induce this ordering has been a mechanical rotation between layers where the twist angle is related to both the moiré period and the resultant functional properties. A fundamentally new mechanism for the emergence of mesoscopic ordering - unrelated to twist - is uncovered in the metal phosphorous trichalcogenide, MnPS3, and is induced by the electron beam. We demonstrate under the beam the formation of periodic hexagonal patterns with several characteristic length scales, explore the local dynamics and atomistic mechanisms, and consider the nanoplasmonics of the system. By exploiting these mechanisms with electron beam patterning, local control of functional and possibly exotic states may be realized. We suggest that this phenomenon not only provides insight into fundamental physics of quantum materials, but also allows for a new design pathway for device applications in developing moiré matter in 2D systems. |
Wednesday, March 16, 2022 4:00PM - 4:12PM |
Q55.00006: Direct Visualization of Magnetic Domains and Moire Magnetism in Twisted 2D Magnets - I Tiancheng Song, Qi-Chao Sun, Eric Anderson, Chong Wang, Jimin Qian, Takashi Taniguchi, Kenji Watanabe, Michael A McGuire, Rainer Stöhr, Di Xiao, Ting Cao, Jörg Wrachtrup, Xiaodong Xu Moiré superlattices of twisted non-magnetic two-dimensional (2D) materials are highly controllable platforms for engineering exotic correlated and topological states. Here, we report emerging magnetic textures in small-angle twisted 2D magnet chromium triiodide (CrI3). Employing single-spin quantum magnetometry, we directly visualize nanoscale magnetic domains and periodic patterns, a signature of moiré magnetism, and measure domain size and magnetization. In twisted bilayer CrI3, we observe the coexistence of antiferromagnetic (AFM) and ferromagnetic (FM) domains with disorder-like spatial patterns. In twisted double trilayer CrI3, AFM and FM domains with periodic patterns appear, in good agreement with the calculated spatial magnetic structures arising from the local stacking-dependent interlayer exchange interactions in CrI3 moiré superlattices. Our results highlight magnetic moiré superlattices as a platform for exploring nanomagnetism. |
Wednesday, March 16, 2022 4:12PM - 4:24PM |
Q55.00007: Direct Visualization of Magnetic Domains and Moire Magnetism in Twisted 2D Magnets - II Eric Anderson, Tiancheng Song, Qi-Chao Sun, Chong Wang, Jimin Qian, Takashi Taniguchi, Kenji Watanabe, Michael A McGuire, Rainer Stöhr, Di Xiao, Ting Cao, J. Wrachtrup, Xiaodong Xu Twist engineering of two-dimensional (2D) materials has proven to be a highly effective method of achieving exotic correlated and topological states. Employing this approach to the 2D magnet chromium triiodide (CrI3) has allowed for quantitative spatial imaging of twist-engineered nanoscale magnetic domains and patterns, detected via Nitrogen Vacancy (NV) magnetometry. Here, we discuss the magnetic behavior of twisted double bilayer CrI3. Using scanning NV magnetometry in conjunction with magneto-optical techniques, we characterize the emergent magnetic domain structure in these samples. Our results highlight the potential of twisted 2D magnets in engineering noncollinear magnetic states. |
Wednesday, March 16, 2022 4:24PM - 4:36PM |
Q55.00008: Evidence of Moiré-induced Noncollinear Spin Textures in Twisted Layered Antiferromagnet Homostructures Xiangpeng Luo, Hongchao Xie, Zhipeng Ye, Gaihua Ye, Shaohua Yan, Yang Fu, Shangjie Tian, Hechang Lei, Kai Sun, Rui He, Liuyan Zhao Moiré engineering developed recently provides an unprecedented venue to design magnetic properties at the atomic scale in the two dimensions. Specifically, in moiré magnets made by twisting two-dimensional (2D) magnetic atomic crystals, the periodic modulations of interlayer exchange coupling, in both strength and sign, can alter the magnetic ground states of constituent 2D magnets and introduce new 2D magnetic phases. While the large pool of 2D magnets discovered so far only features collinear spin structures including simple ferromagnetism and antiferromagnetism, moiré magnets can introduce emergent noncollinear spin textures such as skyrmion lattices and chiral magnetism. In this talk, I will present the observation of noncollinear magnetic order in twisted double bilayer CrI3 through careful magnetic circular dichroism measurements, as well as the evolution of the order as functions of temperature, magnetic field and twist angle. |
Wednesday, March 16, 2022 4:36PM - 4:48PM |
Q55.00009: Band structure engineering of bilayer graphene by superlattice potential Jiacheng Sun Superlattice potential from periodic electric field may allow tunable band structure engineering in 2d materials, providing a new approach for creating novel low-energy electronic properties which may be difficult to achieve in conventional synthesis materials. In this project, we assemble hBN-encapsulated bilayer graphene devices on top of superlattice potential gate created by nanolithography defined antidot array on few-layer graphite. Our approach allows creating on-demand 2D superlattice potential with lattice constant down to ~40nm. We demonstrate modification of the band structure in bilayer graphene and potential emergence of partially flat bands which may facilitate the study of 2d correlated electrons. |
Wednesday, March 16, 2022 4:48PM - 5:00PM |
Q55.00010: Staggered Pseudo Magnetic Field in Twisted Transition Metal Dichalcogenides: Physical Origin and Experimental Consequences Jie Wang, Jiawei Zang, Jennifer Cano, Andrew J Millis The emergent low energy electronic theory of moire materials often includes a `pseudo-magnetic field' arising from the interplay between inter-plane hybridization and moire twist angle. In twisted homobilayer WSe2, the low energy electronic theory is the triangular lattice `moire Hubbard model', which features a spatially dependent pseudo-magnetic field of strength tunable from zero to a large value by varying the interlayer potential difference (displacement field). The pseudo-field produces a staggered flux which is opposite in sign in adjacent plaquettes of the triangular lattice and opposite in sign for the two spin directions. In this talk we show that the pseudo-field has observable consequences, including displacement field tunable Hall sign changes, a different form of the Hofstadter butterfly and spin currents at sample edges and interfaces. Moving beyond homobilayer WSe2 we consider generic consequences of the pseudo-magnetic field, showing how in certain limits it constrains the form of the wave function and the structure of inter-particle interactions. |
Wednesday, March 16, 2022 5:00PM - 5:12PM |
Q55.00011: Unconventional Correlations in TMD Moiré Heterostructures with Functional RG Lennart Klebl, Ammon Fischer, Dante M Kennes, Angel Rubio, Lede Xian, Martin Claassen We study the effect of electron-electron interactions in a variety of moiré heterostructures composed of e.g. WSe2, PtSe2, SnS. The starting point of our analysis is given by few-band tight-binding models that accurately reproduce the flat bands obtained from ab initio simulations. Based on these, we add onsite Coulomb interactions and treat the interacting models using the functional renormalization group. Driven by the interactions, we find a plethora of different spin-density waves and unconventional superconducting instabilities. The correlated phases intrinsically couple spin and momentum degrees of freedom arising from the strong SOC inherent to many TMDs. We demonstrate that TMD moiré heterostructures provide a versatile platform to engineer unconventional, correlated phases of matter and that these phases show topological properties. |
Wednesday, March 16, 2022 5:12PM - 5:24PM |
Q55.00012: In-Silico Study of the Electronic and Magnetic Properties of Functionalized Phosphorene Alvaro Gaspar Rodriguez Mendez, Arezoo Dianat, Leonardo Medrano Sandonas, Rafael Gutierrez, Gianaurelio Cuniberti
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Wednesday, March 16, 2022 5:24PM - 5:36PM Withdrawn |
Q55.00013: Investigation of the Planckian scattering rate in PdCrO2 by high energy electron irradiation Elina Zhakina, Philippa H McGuinness, Marcin Konczykowski, Andrew Mackenzie, Seunghyun Khim PdCrO2 belongs to the delafossite family of extremely pure triangular lattice metals. While its Pd layers are metallic, the CrO2 layers are Mott insulating, and order antiferromagnetically below 37.5 K. PdCrO2 therefore combines the opposite ends of possibilities for the motion of electrons in a solid: a nearly free electron metal and a Mott insulating state, forming an ideal platform to investigate the coupling between such disparate systems [1]. |
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