Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session F62: Young Investigators in Low Dimensional Quantum MaterialsInvited Live
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Sponsoring Units: FECS Chair: Daniel Rizzo, Columbia University |
Tuesday, March 16, 2021 11:30AM - 12:06PM Live |
F62.00001: Facile Production and Light Induced Dynamics of Macroscopic Single Crystal Monolayers and Heterostructures of 2D van der Waals Materials Invited Speaker: Fang Liu Two dimensional (2D) semiconductors and their artificial structures hold great promises for electronic, optoelectronic, and quantum devices. We developed a facile method to disassemble van der Waals (vdW) single crystals layer-by-layer into monolayers with near-unity yield, high quality, and macroscopic dimensions limited only by bulk crystal sizes. This approach takes us one step closer to mass production and commercialization of 2D materials. With these materials, we have quantified several key dynamics in the 2D semiconductors and their heterojunctions. Using time and angle resolved photoemission spectroscopy (TR-ARPES), we quantified bandgap renormalization directly in macroscopic single crystal MoS2 monolayer in the presence of charge carriers, and determined momentum-resolved intervalley conduction band (CB) electron transfer in the WS2/MoS2 heterobilayer, revealing fast scattering dynamics across multiple CB valleys on fs time scale, assisted by fast phonon scattering. These findings reveal versatile optical and electronic responses of the 2D semiconductor systems that can be engineered on demand for future applications. |
Tuesday, March 16, 2021 12:06PM - 12:42PM Live |
F62.00002: Electronic Cascades and Chern Insulators in Twisted Bilayer Graphene Invited Speaker: Dillon Wong Magic-angle twisted bilayer graphene (MATBG) is a remarkable platform for studying strongly correlated electrons due to its incredibly vibrant phase diagram. To understand this phase diagram, we employ gate-tunable scanning tunneling microscopy (STM) and spectroscopy (STS) to probe the energy- and density-dependent electronic structure of MATBG. We find, at a temperature above the transition temperatures for superconductivity and correlated insulators, a cascade of transitions in which the electronic excitation spectrum and chemical potential reset at integer fillings of MATBG’s flat bands [1]. We explain this cascade of transitions in terms of an interplay between strong electronic correlations and the degeneracy of the flat bands, and we extract a measure of the on-site Coulomb repulsion strength between electrons. Upon cooling MATBG to millikelvin temperatures and applying a moderate out-of-plane magnetic field, we observe the formation of insulating gaps that occur at carrier densities that shift with magnetic-field strength [2]. We identify Chern numbers associated with these insulating gaps, showing that strong electron-electron interactions can lead to novel topological states in MATBG. |
Tuesday, March 16, 2021 12:42PM - 1:18PM Live |
F62.00003: Probing moiré superlattices with optical spectroscopy Invited Speaker: Chenhao Jin Moiré superlattices formed between two-dimensional (2D) materials provide new opportunities to engineer novel quantum phenomena, as exemplified by the intriguing observations in twisted bilayer graphene (tBLG). Semiconducting transition metal dichalcogenides (TMDCs) represent another distinct class of moiré system, where the low-energy physics is largely captured by a single-band Hubbard model. In this talk, I will discuss our efforts to study semiconducting moiré superlattices with optical spectroscopy. Taking advantage of the strong light-matter interaction in 2D semiconductors, we access various correlated phases with high sensitivity optical probe. The imaging capability further allows us to look into their spatial variations in wide field. |
Tuesday, March 16, 2021 1:18PM - 1:54PM Live |
F62.00004: Tunable correlated and topological physics in ABC-trilayer graphene on hBN moiré superlattices Invited Speaker: Guorui Chen Two-dimensional materials and their Van der Waals heterostructures are highly tunable and provide an exciting platform to design, create and study novel electronic properties. In this talk, I will take graphene as an example to show how we engineer the electronic properties and experimentally observe the strongly correlated and topological phenomenon in a piece of ABC-trilayer graphene on hBN moiré superlattice. In particular, I will start with a general route to engineer strongly correlated physics in two-dimensional moiré superlattices, and show the experimental realization of a tunable Mott insulator and superconductor in the ABC-trilayer graphene/hBN moiré superlattice. By simply tuning the gate voltages, the large anomalous Hall signals are observed at certain fillings of the topological flat band, and a clear topological Chern insulator is observed at 1/4 filling. Our results demonstrate that ABC-trilayer graphene/hBN moiré superlattice is a very interesting system hosting Mott, superconductivity and topological physics. |
Tuesday, March 16, 2021 1:54PM - 2:30PM Live |
F62.00005: Atom-Scale Engineering of Synthetic Layered Materials Invited Speaker: Andrew Mannix Materials engineered with atomic precision promise unprecedented control over their structure and properties, with profound implications for novel physics and future device technologies. Atomically thin two-dimensional (2D) materials provide a versatile platform for atom-scale engineering: they exhibit a variety of superlative electronic characteristics, and their discrete layered structures and van der Waals (vdW) interlayer bonding enable them to be grown, patterned, and stacked to generate heterostructured solids with atomically precise vertical composition. Additionally, their lateral band structure can be tailored by the formation of moiré superlattices between layers to realize novel quantum phases. In this talk, I will discuss advances in two areas related to the goal of atom-scale engineering via 2D materials: |
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