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 W20: 2D Materials Properties and Physics |
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Sponsoring Units: DCMP Chair: Fei Xue, University of Alabama at Birmingham Room: Room 212 |
Thursday, March 9, 2023 3:00PM - 3:12PM |
W20.00001: Linear response of moire heterostructures to a tilted magnetic field Mohammed M Al Ezzi, Giovanni Vignale, Shaffique Adam It is widely assumed that 2D van der Waals heterostructures should have no valley response to an in-plane magnetic field. However, several recent experimental results in tilted magnetic fields suggest that this assumption is not correct. In this theoretical work, we compute the magnetic susceptibility and magnetization for graphene-based moire systems in a tilted magnetic field. By comparing our results with experimental measurements of the Hall effect in tilted magnetic fields, we estimate how much of the observed angular dependence of the magnetotransport can be understood within a non-interacting picture. This work was supported by the Singapore National Research Foundation Investigator Award (NRF-NRFI06-2020-0003) |
Thursday, March 9, 2023 3:12PM - 3:24PM |
W20.00002: Weak localization as a probe of intervalley coherent order in graphene systems Nemin Wei, Yongxin Zeng, Allan H MacDonald Spontaneous intervalley coherent order is widely conjectured in many graphene multilayer systems, especially in moiré systems with twist induced flat bands. This type of order is hard to be confirmed, however, mainly because experimental signatures are limited. We find that when the valley number conservation in a graphene system is spontaneously broken by time-reversal invariant intervalley coherent order, interference between the time-reversed paths of mean-field quasiparticles can yield a quantum correction to the Drude conductivity. Intervalley coherent states can exhibit weak localization or antilocalization depending on whether they belong to the orthogonal or symplectic symmetry class. Quantum interference corrections to transport can be a smoking gun for intervalley coherence, provided that intervalley scattering induced by atomically sharp defects is negligible. Our analysis motivates low-temperature weak-field magnetoresistance measurements in graphene mutlilayers in which time-reversal invariant intervalley coherent order is suspected. |
Thursday, March 9, 2023 3:24PM - 3:36PM |
W20.00003: Electronic and optical properties of layered InSe structures from Density Functional Theory and Quantum Monte Carlo methods Hyeondeok Shin, Abdulgani Annaberdiyev, Jovan J Nelson, Nathaniel P Stern We performed Density Functional Theory (DFT) and Quantum Monte Carlo (QMC) calculations of layered InSe to investigate its optical and electronic properties. The post-transition metal chalcogenide InSe has attracted significant attention because of its potential applications in energy conversion, spintronic device, and chemical sensing. While bulk InSe has been known to be a semiconductor with ~ 1.2 eV band gap, electronic and optical properties of the mono- or multi-layer forms are not well known experimentally. We have used ab-initio DFT method to predict their electronic properties; however, we found that the DFT results vary strongly with the choice of exchange-correlation functional. Our DFT results cannot conclusively determine if InSe polytypes possess a direct or indirect gap, and the band gap is entirely closed in bulk β-InSe when using plain DFT, while it is experimentally known as a direct gap semiconductor. Using fixed-node diffusion Monte Carlo (DMC), we seek to achieve improved electronic and optical properties and investigate the interplay between interlayer interactions and electron correlations on InSe polytypes. In addition, our QMC calculations of the monolayer and bilayer provide further insights into the electronic and optical properties of InSe structures. |
Thursday, March 9, 2023 3:36PM - 3:48PM |
W20.00004: Nonlinear Optical Imaging of In-Plane Anisotropy in two-dimensional SnS Emmanuel Stratakis, G M Maragkakis, S Psilodimitrakopoulos, L. Mouchliadis, A Lemonis, George Kioseoglou Two-dimensional (2D) tin (II) sulfide (SnS) crystals belong to a class of orthorhombic semiconducting materials with remarkable properties, such as in-plane anisotropic optical and electronic response, and multiferroic nature. The 2D-SnS crystals exhibit anisotropic response along the in-plane armchair (AC) and zigzag (ZZ) crystallographic directions, offering an additional degree of freedom in manipulating their behavior. Here we take advantage of the lack of inversion symmetry of the 2D-SnS crystal to perform polarization-resolved SHG (P-SHG) nonlinear imaging of the in-plane anisotropy. The P-SHG data are fitted with a nonlinear model, allowing to calculate the AC/ZZ orientation from every point of the 2D crystal and to map with high-resolution the AC/ZZ direction of several 2D-SnS flakes in the same field of view. It is found that the P-SHG intensity polar patterns are associated with the crystallographic axes of the flakes and with the relative strength of the 2ndorder nonlinear susceptibility tensor in different directions. Οur method provides quantitative information of the in-plane anisotropy of orthorhombic 2D-crystals, offering great promise for performance characterization during device operation in the emerging optoelectronic applications of such crystals. |
Thursday, March 9, 2023 3:48PM - 4:00PM Author not Attending |
W20.00005: Cyclotron resonance in bilayer graphene in the hydrodynamic limit Yashika Kapoor, Joseph R Cruise, Alexander Seidel, Giovanni Vignale, Erik Henriksen When electron-electron scattering dominates over electron-phonon and impurity scattering, fluid-like flow of charge carriers results, where this dynamic flow is governed by classical fluid mechanics. In a narrow window of temperature and carrier density, the hydrodynamic limit can be achieved in monolayer graphene. Recent work suggests that the hydrodynamic regime is more readily achievable in bilayer graphene as it exhibits no temperature cutoff and providers a wider window in carrier density, which suggests that it is better suited for achieving this hydrodynamic limit than monolayer graphene. In the presence of a magnetic field, a hydrodynamic cryotron resonance arises that departs from the kinematic cyclotron frequency. There is a finite parameter space in temperature and magnetic field in which this departure can be observed, making it possible to explore cyclotron resonance in bilayer graphene using the magneto-optical infrared spectroscopy within and outside the hydrodynamic window. We will present initial measurements of resonant absorption in hydrodynamic bilayer graphene. |
Thursday, March 9, 2023 4:00PM - 4:12PM |
W20.00006: Nonlinear nano-imaging of electronic coherence in gated graphene Andreij Gadelha, Wenjin Luo, Fabiano Santana, Alexey Belyanin, Markus B Raschke The Dirac cone band structure and zero energy band gap of graphene allow for a multitude of resonant nonlinear optical interaction pathways not possible in conventional materials. Further, gate voltage Fermi level (Ef) tuning enables switching and controlling the nonlinear conversion efficiency. However, underlying spatial heterogeneities, including selection rules and electronic coherence, are yet poorly understood, and expected to be in part fundamentally distinct in the optical near-field regime. Here we apply ultrafast nonlinear nanoscopy in adiabatic nano-focusing on gated ultra-clean graphene devices. We investigate the graphene response in four-wave mixing (FWM) as a function of gate voltage changing Ef. Due to Pauli blocking, the far-field FWM intensity is only expected to change for Fermi level shifts about 0.8 eV from the neutrality point under our experimental conditions. In contrast, we observe a different near-field gate dependency with Ef ~0.4 eV, suggesting a new nonlinear nano-optics regime with non-local enhancement and associated with a quantum Doppler effect. |
Thursday, March 9, 2023 4:12PM - 4:24PM |
W20.00007: Lieb Lattice, Anomalous 2D Raman modes and Localized Defect States in a Novel 2D Metal Morgan Thinel, Simon E Turkel, Christie S Koay, Asish K Kundu, Taketo Handa, Daniel G Chica, Raquel Queiroz, Abhay N Pasupathy, Xiaoyang Zhu, Xavier Roy Here, we report the synthesis and characterization of a novel air stable layered van der Waals metal with tetragonal symmetry. First, the metallic character and electronic structure of this material were characterized in bulk crystals via scanning tunneling microscopy (STM) and angle resolved photoemission spectroscopy (ARPES). The bulk crystals exhibit high density of state resonances corresponding to flat bands. Defects in the bulk crystals show localized defect states under STM, an as yet unreported phenomenon in metallic crystals. This can be attributed to the electronic Lieb lattice that arises from strong interactions between surface atoms arranged in a square geometry. Raman spectroscopy and STM of monolayer exfoliated flakes are evidence for the long-term stability of this metal under ambient conditions. Notably, new, strongly Raman active modes appear in few-layer samples yet are absent in bulk crystals. As such, we have a new air stable metal, which allows for a wide range of applications as a good conductor for nanoscale devices involving other 2D materials and heterostructures. Additionally, evidence for flat bands and a Lieb lattice support the use of this material as a template in which to induce exotic many-body states. Finally, the emergence of high intensity Raman modes in the few-layer limit is a previously unobserved phenomenon. This material is of fundamental interest to further our understanding of the mechanisms which yield new physics in novel 2D materials. |
Thursday, March 9, 2023 4:24PM - 4:36PM |
W20.00008: Control of resonance effects in third-harmonic generation from graphene using the ion-gel gating technique Daiki Inukai, Takeshi Koyama, Kenji Kawahara, Hiroki Ago, Hideo Kishida Single-layer graphene shows various third-order nonlinear optical (NLO) responses including two-photon absorption, four-wave mixing, and optical Kerr effect. Third-harmonic generation (THG) is one of the simplest third-order NLO responses. In this research, we focus on the Fermi level (EF) dependence of THG from graphene. We prepared electrochemical doping devices for graphene using ion-gel based on an ionic liquid [EMIM][TFSI]. The EF as a function of applied voltage was determined by the Raman spectroscopy. The experiment of THG was performed using the Maker fringe method. This method enables us to obtain both the intensity and phase of the electric field of THG. As a result of the measurement, we observed the variation of THG due to doping. To discuss the EF dependence of THG from graphene, we carried out a model calculation for third-order nonlinear optical susceptibility. Based on the experimental and calculated results, we discuss the dominant resonance process and its control in THG from graphene. |
Thursday, March 9, 2023 4:36PM - 4:48PM |
W20.00009: Fabrication of 2D Heterostructures with Air Stable van der Waals Magnetic Material CrPS4 Jeremy D Low, Marc Bockrath Stacking van der Waals (vdW) materials can lead to new behavior in two-dimensional (2D) heterostructures as a result of interlayer interactions. Additionally, moiré engineering allows for additional tunability by modifying the lattice mismatch or twist angle between two vdW crystals. CrPS4 is an air stable antiferromagnetic 2D vdW crystal, making it a good candidate for stacking, to probe spin-orbit-coupling, superconductivity, and other strongly correlated phenomena in 2D materials. Twisted bilayer CrPS4 (TBCrPS4) is predicted to demonstrate coexisting ferromagnetic-antiferromagnetic ground states for small twist angles1, allowing for further tunability. Here we discuss exfoliation techniques for maximizing yield and size of thin CrPS4 flakes toward fabricating CrPS4 and TBCrPS4 heterostructures. |
Thursday, March 9, 2023 4:48PM - 5:00PM |
W20.00010: Optical conductivity as a probe of the interaction-driven metal in rhombohedral trilayer graphene Rodrigo A Soto Garrido, Vladimir Juricic, Enrique Munoz Rhombohedral trilayer graphene (RTG) has been the focus of special interest in the last years, since it hosts a variety of interaction-driven phases, with the metallic ones yielding exotic superconducting orders upon doping [H. Zhou et al, Nature 598, 429 (2021); ibid. 598, 434 (2021)]. In this work we compute the optical conductivity (using the low-energy effective theory ) for the three proposed paramagnetic metallic ground states: a fully gapped valence-bond state, the bond-current state and the rotational symmetry breaking charge-density wave. We show that the optical conductivity presents specific features for each of the aforementioned states and can therefore be used to distinguish between these different paramagnetic metallic ground states. |
Thursday, March 9, 2023 5:00PM - 5:12PM |
W20.00011: Observation on the odd-even layer-number effect in WTe2 with laser-based micro-ARPES Masato Sakano, Satoru Masubuchi, Yuma Tanaka, Shota Okazaki, Takuya Nomoto, Atsushi Oshima, Kenji Watanabe, Takashi Taniguchi, Ryotaro Arita, Takao Sasagawa, Tomoki Machida, Kyoko Ishizaka We investigate the electronic band dispersions of multilayer WTe2 (2–5 layers), by performing laser-based micro-focused angle-resolved photoelectron spectroscopy on exfoliated ?akes sorted by number of layers (n). We observe the 30–70-meV spin splitting of valence bands manifesting in even n as a signature of stronger structural asymmetry. Our result fully demonstrates the possibility of the large energy-scale band and spin manipulation through the ?nite-n stacking procedure. The developed sample fabrication procedure for ARPES in this study should be applicable to a wide range of micro-flakes samples, such as heterostructures and twisted materials. |
Thursday, March 9, 2023 5:12PM - 5:24PM |
W20.00012: Breaking of spatial inversion symmetry in anti-parallel-stacked ReSe2 Shunsuke Akatsuka, Masato Sakano, Takato Yamamoto, Takuya Nomoto, Ryotaro Arita, Ryoga Murata, Takao Sasagawa, Kenji Watanabe, Takashi Taniguchi, Miho Kitamura, Koji Horiba, Katsuaki Sugawara, Seigo Souma, Takafumi Sato, Hiroshi Kumigashira, Keisuke Shinokita, Kazunari Matsuda, Satoru Masubuchi, Tomoki Machida, Kyoko Ishizaka The development of mechanical exfoliation and dry-transfer techniques has made it possible to stack two-dimensional flakes dynamically and fabricate new materials that cannot be synthesized through thermodynamic processes. In such composite flakes, changes in the symmetry of the total system lead to a variety of emergent physical properties that would not appear in each component flake alone. Here, we fabricated an anti-parallel-stacked bilayer ReSe2, which is expected to lose the spatial-inversion-symmetry by stacking the centrosymmetric monolayer flakes in the opposite directions. By micro-focused angle-resolved photoemission spectroscopy and second harmonic generation, we successfully observed the band dispersions and the artificially induced spatial inversion symmetry breaking in the anti-parallel-stacked bilayer ReSe2. Our result demonstrates the potential for creating new materials that can exhibit spintronic functions and Berry-curvature-related physical phenomena by controlling the presence or absence of spatial inversion symmetry. |
Thursday, March 9, 2023 5:24PM - 5:36PM |
W20.00013: Electronic correlations in the normal state of twisted bilayer graphene Maria J Calderon, Anushree Datta, Alberto Camjayi, Elena Bascones The discovery of insulating states, superconductivity and other broken symmetry states in magic angle twisted bilayer graphene and other moiré heterostructures has marked a new era in the research of correlated materials. In these systems, narrow bands can lead to an enhanced importance of interactions on the electronic properties both in symmetry broken and in non-ordered states. In this talk, we will explore the effect of correlations in the normal, non-ordered state, of twisted bilayer graphene, using dynamical mean field theory. We will show how the spectral weight is strongly reorganized due to correlations. This reorganization in the normal state may also have important consequences for the electronic properties of the ordered states. |
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