Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session B55: Physical Properties of 2D Materials and SuperlatticesRecordings Available
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Sponsoring Units: DCMP Room: Hyatt Regency Hotel -Adler |
Monday, March 14, 2022 11:30AM - 11:42AM |
B55.00001: Immense Fano Resonance Induced by Half van der Waals Metals Kunyan Zhang, Rinu Abraham Maniyara, Yuanxi Wang, Thuc T Mai, Maxwell Wetherington, Timothy Bowen, Slava Rotkin, Angela R Hight Walker, Vincent H Crespi, Joshua A Robinson, Shengxi Huang Interference between quasiparticles in solid-state materials provides an in-depth understanding of the coupling mechanism, such as electron-phonon or phonon-phonon coupling, and the optical and electronic properties of the material. Fano resonance, an interference effect between a discrete excited state and a continuum of excited states, is characterized by an asymmetric line shape in the scattering spectrum with an asymmetry parameter 1/q. For Fano resonance that involves a Raman-active phonon, the degree of asymmetry is typically small due to the relatively weak interference. In this work, we present Fano resonance in an atomically thin metal intercalated between graphene and SiC, where the degree of asymmetry in Fano resonance is over two orders of magnitude higher than in previous reports. This asymmetry factor can also be controlled by physical parameters including temperature and excitation wavelength, whose mechanism is studied by first-principles calculations. The ability to tune the strength of Fano resonance paves the way toward engineering interference effect between quasiparticles at the nanoscale limit. |
Monday, March 14, 2022 11:42AM - 11:54AM |
B55.00002: Emulating twisted double bilayer graphene with a multiorbital optical lattice Junhyun Lee, Jedediah H Pixley We theoretically explore how to emulate twisted double bilayer graphene with ultracold atoms in multiorbital optical lattices. In particular, the quadratic band touching (QBT) of Bernal stacked bilayer graphene is emulated using an optical lattice with px, py, and dx2−y2 orbitals on each site, while the effects of a twist are captured through the application of an incommensurate potential. The QBT is stable while the system undergoes an Anderson-like delocalization transition in momentum space and re-enters the QBT phase, which occurs concomitantly with a strongly renormalized single-particle spectrum. The band structure is described perturbatively in the quasiperiodic potential strength where the transition is indicated by the diverging effective mass, which agrees well with the exact numerical results for a weak potential strength. |
Monday, March 14, 2022 11:54AM - 12:06PM |
B55.00003: Laser-Induced Dynamic Alignment and Nonlinear-Like Optical Transmission in Liquid Suspensions of 2D Atomically Thin Nanomaterials Yanan Wang, Qiuhui Zhang, Feng Lin, Yingjie Tang, Peihong Cheng, Xufeng Zhou, Zhuan Zhu, Yayao Ma, Zhaoping Liu, Dong Liu, Laichen Liu, Chengzhen Qin, Zhongchen Chen, Zhiming Wang, Jiming Bao Thanks to the development of liquid exfoliation techniques, liquid suspensions of two-dimensional (2D) atomically thin nanomaterials have attracted enormous research interest as platforms to explore nonlinear optical phenomena. However, in most reported studies, the intrinsic geometry and consequential optical anisotropy of these low-dimensional nanomaterials have been overlooked. In this work, we take graphene and graphene oxide as examples and synergize birefringence imaging and computational fluid dynamics to reveal the laser-induced dynamic alignment in these liquid suspensions. Moreover, the influence of the ordered states and birefringence on optical transmission has been systematically scrutinized in Z-scan measurements. We find out that saturable absorption-like and optical limiting-like transmission, observed under both continuous-wave and nanosecond pulsed lasers, should not be misinterpreted as third-order nonlinear effects from electronic or dielectric polarization of nanomaterials. The understanding of 2D atomically thin nanomaterials, solvent fluids, as well as their interactions with laser beams developed here provides valuable guidelines for designing optical transmission measurements and investigating nonlinear optical properties of nanomaterial suspensions. |
Monday, March 14, 2022 12:06PM - 12:18PM |
B55.00004: Superconductivity in the twisted bilayer transition metal dichalcogenide WSe2 Mathieu Belanger, Jerome Fournier, David Senechal The observation of superconductivity and correlated insulating states in twisted bilayer graphene has brought to the forefront the topic of twisted systems. The reproducibility in graphene-based systems can be difficult, hence new materials possessing similar features, like transition metal dichalcogenides (TMD), are being considered. The enhancement of electronic correlations by the introduction of a small twist angle between the two layers can be seen in a TMD bilayer such as twisted WSe2. Experimental observations in this TMD have revealed the presence of flat energy bands for a continuum of angles. Evidence of superconductivity was also reported (Wang, L. et al., Nat. Mater. 19, 861–866 (2020)). We report on an investigation of superconductivity within an effective Hubbard model defined on a triangular lattice for twisted WSe2. We use the variational cluster approximation (VCA) and cluster dynamical mean field theory (CDMFT) to take into account short-range correlations exactly, and work at zero temperature with an exact-diagonalization impurity solver. We find a superconducting phase of type d+id away from half-filling, that can be tuned by the twist angle and by the application of a perpendicular electric field. |
Monday, March 14, 2022 12:18PM - 12:30PM |
B55.00005: Computational Design of Moiré Assemblies aided by Artificial Intelligence Gabriel R Schleder, Stephen T Carr, Georgios Tritsaris Two-dimensional (2D) layered materials offer a materials platform with potential applications from energy to information processing devices. Although some single- and few-layer forms of materials such as graphene and transition metal dichalcogenides have been realized and thoroughly studied, the space of arbitrary layered assemblies is still mostly unexplored. The main goal of this work is to demonstrate precise control of layered materials' electronic properties through careful choice of the constituent layers, their stacking, and relative orientation. Physics-based and AI-driven approaches for the automated planning, execution, and analysis of electronic structure calculations are applied to layered assemblies based on prototype one-dimensional (1D) materials and realistic 2D materials. We find it is possible to routinely generate moiré band structures in 1D with desired electronic characteristics such as a bandgap of any value within a large range, even with few layers and materials (here, four and six, respectively). We argue that this tunability extends to 2D materials by showing the essential physical ingredients are already evident in calculations of two-layer MoS2 and multi-layer graphene moiré assemblies. |
Monday, March 14, 2022 12:30PM - 12:42PM |
B55.00006: A position-dependent ab initio tight-binding model for twisted TMD bilayers Kemal Atalar, Johannes C Lischner, Arash A Mostofi The discovery of superconducting and correlated insulating states in magic-angle twisted bilayer graphene has led to intense interest in other moiré materials. Twisted bilayer transition metal dichalcogenides (TMDs), for example, have been shown to exhibit correlated insulating states at different fillings, possible superconducting behaviour [1], and exotic optical properties [2]. |
Monday, March 14, 2022 12:42PM - 12:54PM |
B55.00007: Chiral Phonons in Moiré Superlattices Nishchay Suri, Chong Wang, Yinhan Zhang, Di Xiao We discover chiral phonons at the lowest-energy bands in moiré superlattices. The moiré chiral phonons we uncover are the collective excitations of the stacking domains. Their origin is uniquely attributed to the stacking configurations whose interlayer binding energy breaks the C2z symmetry on the moiré length scale. Within elastic theory, we use a general symmetry analysis to provide a complete classification of van der Waals heterostructures in respect to hosting moiré chiral phonons and show the calculation for twisted MoS2 as an example. We present a low-energy effective model to qualitatively understand the moiré chiral phonons and show that it captures the essential physics remarkably well. Our result potentially opens up new possibilities in phononic twistronics as the moiré chiral phonons have high tunability, moiré scale wavelengths, excitation energies in only a few meV, and can possibly be mechanically excited. |
Monday, March 14, 2022 12:54PM - 1:06PM Withdrawn |
B55.00008: Dark and leaky exciton condensates in transition metal dichalcogenide moiré bilayers Benjamin Remez, Nigel R Cooper We show that the "dark condensates" that arise when excitons form a Bose-Einstein condensate in a material with an indirect bandgap are not completely dark to optical emission. Rather, such states are "leaky condensates" in which optical emission is facilitated by many-body interactions. We analyze the properties of these leaky condensates in the context of twisted bilayers of transition metal dichalcogenides, which host strongly interacting excitons and an indirect bandgap. We show that, even though excitonic condensates in these materials can break translational symmetry, direct emission remains forbidden by a robust rotational symmetry. The optical signatures at low temperatures are dominated by the interaction-driven "leaky" emission, with distinctive qualitative features. |
Monday, March 14, 2022 1:06PM - 1:18PM |
B55.00009: Altering the reflection phase for nano-polaritons: a case study of hyperbolic surface polaritons in Hexagonal Boron Nitride Mingyuan Chen, Stephen Sanders, Jialiang Shen, Jiahan Li, Eli Harris, Cheng-Chien Chen, Qiong Ma, James H Edgar, Alejandro Manjavacas, Siyuan Dai
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Monday, March 14, 2022 1:18PM - 1:30PM |
B55.00010: Deterministically Creating Single-Photon Emitters in Hexagonal Boron Nitrides on Chip-Compatible Substrates Xiaohui Xu, Zachariah O Martin, Demid Sychev, Alexei S Lagutchev, Yong Chen, Takashi Taniguchi, Kenji Watanabe, Vladimir M Shalaev, Alexandra Boltasseva Two-dimensional hexagonal boron nitride (hBN) that hosts room-temperature single-photon emitters (SPEs) is promising for quantum information applications. An important step towards the practical application of hBN is the on-demand, position-controlled generation of SPEs. Strategies reported for deterministic creation of hBN SPEs either rely on substrate nanopatterning that is not compatible with integrated photonics, or utilize radiation sources that might introduce unpredictable damage or contamination to hBN. Here, we report a radiation- and lithography-free route to deterministically activate hBN SPEs by nanoindentation with an atomic force microscope (AFM). The method applies to hBN flakes on flat silicon-dioxide-silicon substrates that can be readily integrated into on-chip photonic devices. The achieved SPE yields are above 30% for multiple indent sizes, and a maximum yield of 36% is demonstrated for indents around 400 nm. Our results mark an important step towards the deterministic creation and integration of hBN SPEs with photonic and plasmonic devices. |
Monday, March 14, 2022 1:30PM - 1:42PM |
B55.00011: High-quality bottom-up grown van der Waals phonon polariton systems Shangjie Yu, Yue Jiang, John A Roberts, Xiaolin Zheng, Tony F Heinz, Jonathan A Fan In the infrared range, van der Waals materials have emerged as an exciting class of materials due to their ability to support high-quality phonon polariton excitations. The ability to localize and guide light in extremely deep subwavelength leads to fundamental light-matter interactions and functional applications such as sensing and waveguiding in ultracompact devices. In this study, we demonstrate that bottom-up synthesized α-MoO3 micro- and nano-structures are ultrahigh quality hyperbolic phonon polaritonic systems through material characterization and near-field optical measurement. No lithography or ion milling is needed to define the structures, and thus fabrication-induced damage or contamination on the vdW material or the substrate material can be voided. Based on systematic improvement of the sample preparation, we have achieved ultrabroadband visualization of the Fabry-Pérot resonances over four Reststrahlen bands and revealed high quality factors in an α-MoO3 nanoresonator. The mode figure of merit analysis confirms that α-MoO3 structures on ultrasmooth gold is good material combination for high-mode-compression and low-loss polaritonics. |
Monday, March 14, 2022 1:42PM - 1:54PM |
B55.00012: Highly polarized optical responses in bulk black phosphorus from high energy states Leonard Schue, Felix Antoine Goudreault, Ariete Righi, Valerie Lefebvre, Emile Godbout, Marcos Pimenta, Michel Cote, Sebastien Francoeur, Richard Martel Black phosphorus (BP) is unique among other layered materials owing to its homonuclear lattice and strong structural anisotropy. While recent investigations on few layers BP have extensively explored the in-plane anisotropy, much less attention has been given to the out-of-plane direction of the bulk crystal. Here, polarization-resolved spectroscopy measurements are performed on bulk BP along the zigzag, out-of-plane and armchair directions under visible light excitation to determine the complete optical response of the crystal. Under out-of-plane polarized excitation, an unexpected PL emission is detected near 1.75 eV, which is far above the ∼0.3 eV band gap energy. Photoluminescence excitation and Raman energy maps indicate the presence of an unreported resonance at ∼2.3 eV in the out-of-plane direction, which gives rise to the above-bandgap luminescence and an enhancement of the Ag phonon modes intensity. This intriguing resonance is analyzed using the complex dielectric permittivity of bulk BP obtained by DFT calculations. The calculated strongly polarized dipolar transitions in bulk crystals are fully consistent with the optical anisotropy observed here. |
Monday, March 14, 2022 1:54PM - 2:06PM |
B55.00013: Excitonic structure and extremely strong and narrow optical absorption of C3N and C3B monolayer Zhao Tang, Yabei Wu, Fanhao Jia, Greis J. Cruz, Weiyi Xia, Wenqing Zhang, Peihong Zhang The graphene-like 2D materials C3N and C3B have attracted increasing attention due to their various potential applications. Compared with graphene, C3N is electron rich, whereas C3B is electron deficient. Both materials have a moderate band gap and possess nearly parallel valence and conduction bands [1,2] which may be beneficial for strong optical absorption. In this work, we have carried out fully converged calculations to investigate the excitonic structures and optical properties of C3N and C3B within the GW and Bethe-Salpeter equation (BSE) approach. We find that parallel band edges give rise to extremely strong and narrow excitonic absorption. Details of the excitonic structure will also be discussed. |
Monday, March 14, 2022 2:06PM - 2:18PM |
B55.00014: Measuring pressure-induced phase transformations in layered ferrielectric CuInP2S6-In4/3P2S6 self-assembled heterostructures Rahul Rao, Benjamin S Conner, Ryan Selhorst, Michael A Susner Layered multi-ferroic materials exhibit a variety of functional properties that can be tuned by varying the temperature and pressure. As-synthesized CuInP2S6 is a layered material that displays ferrielectric behavior at room temperature. When synthesized with Cu deficiencies, CuInP2S6 spontaneously phase segregates to form ferrielectric CuInP2S6 (CIPS) and paraelectric In4/3P2S6 (IPS) domains in a two-dimensional self-assembled heterostructure. Here, we study the effect of hydrostatic pressure on the structure of Cu-deficient CuInP2S6 by Raman spectroscopy measurements up to 20 GPa. Detailed analysis of the frequencies, intensities, and linewidths of the Raman peaks reveals four discontinuities in the spectra around 2, 10, 13 and 17 GPa. At ~2 GPa, we observe a structural transition initiated by the diffusion of IPS domains, which culminates in a drastic reduction of the number of peaks around 10 GPa. We attribute this to a possible monoclinic-trigonal phase transition at 10 GPa. At higher pressures (~ 13 GPa), significant increases in peak intensities and sharpening of the Raman peaks suggest a bandgap-lowering and an isostructural electronic transition, with a possible onset of metallization at high pressure. When pressure is released, the structure again phase-separates into two distinct chemical domains within the same single crystalline framework- however, these domains are much smaller in size than the as-synthesized material resulting in suppression of ferroelectricity through nanoconfinement. Hydrostatic pressure can thus be used to tune the electronic and ferrielectric properties of Cu-deficient layered CuInP2S6. |
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