Bulletin of the American Physical Society
APS March Meeting 2021
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session C41: Fundamental Physics Using 2D SystemsLive

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Sponsoring Units: DCMP Chair: James Hone, Columbia Univ 
Monday, March 15, 2021 3:00PM  3:12PM Live 
C41.00001: QValley Quasiparticle Interference in FewLayer Transition Metal Dichalcogenides Patrick Cheung, YanFeng Zhou, Fan Zhang Quantum transport experiments have provided compelling evidence for the threefold flavors of the Qvalley electrons in fewlayer transition metal dichalcogenides (TMD). We study the quasiparticle interference (QPI) due to Qvalley electrons scattering off localized impurities, which modifies the local density of states. In the quantum Hall regime, all the TMD oddlayers thicker than bilayer exhibit Landau level triplets. When a Landau level triplet is onethird filled or empty, the flavor SU(3) symmetry is broken in the ferroelectric nematic ground states tunable by an inplane electric field and an outofplane magnetic field. We show the QPI patterns of such flavor states, which can be probed by scanning tunneling spectroscopy. 
Monday, March 15, 2021 3:12PM  3:24PM Live 
C41.00002: HeavyFermion Physics in a Transition Metal Dichalcogenide Moiré Heterostructure Ajesh Kumar, Naichao Hu, Andrew C Potter, Allan MacDonald We propose a realization of heavyfermion physics in suitablydesigned trilayer transition metal dichalcogenide heterostructures, which enable gatetuning across the heavyfermion critical point in a single device. The trilayer consists of an aligned WX_{2} bilayer on a MoX_{2 }monolayer with a small relative twist angle. Using dual gates, the Fermi level in the top WX_{2 }layer, which experiences weak moiré modulation, can be placed between the lower and upper Hubbard subbands of the strongly modulated narrowband in the lower WX_{2 }layer. Electrons in the metallic and insulating layers are analogous to the d and felectrons in heavyfermion materials, and their spins have an antiferromagnetic Kondo coupling due to interlayer hybridization. We calculate the leading hightemperature Kondo corrections to the resistivity and use these to estimate where Kondo physics is observable. We also predict characteristic fingerprints of possible heavy Fermi liquid to quantum spin liquid phase transition and other quantum criticality scenarios in transport, capacitance and optical measurements. 
Monday, March 15, 2021 3:24PM  3:36PM Live 
C41.00003: Flavor Quantum Dots and Artificial Quark Model in Transition Metal Dichalcogenides Peng Peng Zheng, Zhiqiang Bao, Patrick Cheung, Fan Zhang We show that the triply degenerate Q valleys in fewlayer transition metal dichalcogenides provide a unique platform for exploring the rare flavor SU(3) symmetry in quantum dot geometry. The single and double dots are reminiscent of the quark model and eightfold way, and their manybody triplets and octets may be regarded as artificial quarks and hadrons. For the artificial quark transistor, each level hosts one central and two side Coulomb peaks of irrational height ratios, and flavor Kondo effects occur at 1/3 and 2/3 fillings with fractional conductance quantization in the unitary limit. 
Monday, March 15, 2021 3:36PM  3:48PM Live 
C41.00004: Nematic superconducting state promoted by electromagnetic gauge field fluctuations Virginia Gali, Rafael Fernandes Motivated by the recent observation of nematic superconductivity in twisted bilayer graphene (TBG), we present a theory for the pairing state symmetry of twocomponent pwave and dwave unconventional superconductors on the triangular lattice. Here, we show that electromagnetic (EM) fluctuations play a crucial role in selecting between chiral (p+ip and d+id) and nematic (p+p and d+d) solutions. Specifically, we derive an effective free energy for the twocomponent superconducting order parameter after integrating out the EM fluctuations just above the superconducting transition. The effects of such fluctuations are encoded in a nonanalytic term that is cubic in the order parameter, and generally favors a nematic superconducting state being realized below T_{c}. The quartic terms of the free energy are little affected by the EM fluctuations, and continue to favor a chiral state. The competition between cubic and higher order terms leads to a phase diagram in which the nematic solution emerges over a wide parameterspace region where the chiral solution would be favored in the meanfield approach. We discuss the stability of the fluctuationinduced nematic phase and explain how our results may be applied to TBG and other nematic superconductors. 
Monday, March 15, 2021 3:48PM  4:00PM Live 
C41.00005: Universal Scaling for Electron Transmission in Nearly Ballistic And Quantum Dragon Nanodevices Mark Novotny, Tomas Novotny The electrical conductance is proportional to the electron transmission probability T(E_{F}) at the Fermi energy E_{F} when a nanodevice is connected to a source and sink of electrons via long leads. We study via a tightbinding model two types of devices that have T(E)=1 for all energies that propagate through the attached leads. Ballistic nanodevices have no disorder, and using Bloch wavefunction analysis, have T(E)=1. A quantum dragon nanodevice [1] has arbitrarily strong correlated disorder but still has T(E)=1. Adding uncorrelated random site disorder to models for quantum dragon or for ballistic nanodevices one can calculate a transmission T_{ave}(E) that averages over the Fano resonances in T(E). Using NEGF (NonEquilbrium Green's Function) methods, we obtain universal scaling forT_{ave}(E) in two different scaling regimes. The scaling is tested for pure and disordered graphene and singlewalled carbon nanotubes, and for numerous quantum dragon nanodevices. We show the scaling works extremely well for any nearly ballistic or nearly quantum dragon nanodevice. 
Monday, March 15, 2021 4:00PM  4:12PM Live 
C41.00006: A DMRG study of the extended Hubbard model on the triangular lattice Yiqing Zhou, Donna Sheng, EunAh Kim Moire systems provide a rich platform for studies of strong correlation physics. A recent experiment with transition metal dichalcogenide (TMD) bilayer realized an experimental simulation of the extended Hubbard model on a triangular lattice[1]. Inspired by this experiment, we explore the charge order phenomena of the extended Hubbard model on the triangular lattice using the density matrix renormalization group (DMRG). 
Monday, March 15, 2021 4:12PM  4:24PM Live 
C41.00007: Nonlocal interactions in transition metal dichalcogenide heterobilayer moiré superlattices Nicolás MoralesDurán, Pawel Potasz, Allan MacDonald Moiré superlattices formed in twodimensional semiconductor heterobilayers provide a new realization of Hubbardlike physics in which the number of charge carriers per effective atom can be tuned through large ranges with electrical gates. Electrons or holes are less strongly attracted to effective lattice sites defined by external potential minima in moiré superlattices than in atomic lattices, because the confining potential is weaker than the attractive potential of positively charged atomic nuclei. As a consequence, nonlocal interaction terms like interactionassisted hopping and intersiteexchange have a larger importance in moirématerial generalized Hubbard models. We discuss the influence of this difference on the metalinsulator phase transition and on magnetic insulating states at halffilling, by means of an exact diagonalization study of the electronic properties of narrow moiré bands. We also address the strong particlehole asymmetry in physical properties as a function of doping relative to halffilling. 
Monday, March 15, 2021 4:24PM  4:36PM Live 
C41.00008: Electronic compressibility study of transition metal dichalcogenide moiré superlattices Tingxin Li, Jiacheng Zhu, Jie Shan, Kin Fai Mak Moiré superlattices built on 2D transition metal dichalcogenide (TMD) semiconductors have presented a highly controllable platform to study Hubbard model physics on a triangular lattice. In this talk, we will present electronic compressibility study of TMD heterobilayer moiré superlattices. We have observed a series of incompressible chargeordered states at both integer and fractional filling factors of the moiré superlattice. Both the thermodynamic gaps and the transition temperatures of these incompressible states are measured, allowing us to obtain the characteristic energy scales of the system. Furthermore, a chargeorderenhanced capacitance has been observed, which is driven by the devicegeometrydependent electronelectron interaction. 
Monday, March 15, 2021 4:36PM  4:48PM Live 
C41.00009: Order to Disorder in Quasiperiodic Systems david morison, Benjamin Murphy, Elena Cherkaev, Kenneth Golden Four decades since the discovery of quasicrystals, the material properties arising from quasiperiodic microgeometry remain a topic of theoretical intrigue and engineering utility. Here we introduce a class of quasiperiodic media with novel macroscopic behavior. As the microgeometry of a Moiré system is tuned, the transport properties switch from those of ordered to randomly disordered materials in a fashion which parallels the Anderson localization transition, even though there are no scattering or interference effects at play. This transition is evident within an integral representation that applies broadly to the effective electrical, thermal, elastic, and optical properties of twophase composite media. This representation distills the relationship between microgeometry and bulk transport into the spectral characteristics of an operator, which is analogous to the Hamiltonian in quantum transport phenomena. Periodic media display sharp resonances, band gaps, and spatially extended eigenstates separated by "mobility edges" of localized states. As we tune system parameters to aperiodicity and disorder, level repulsion increases as the spectral properties transition toward obeying universal WignerDyson statistics. 
Monday, March 15, 2021 4:48PM  5:00PM Live 
C41.00010: Realizing the Kondo lattice Model in Electron Doped Heterogeneous TMD Bilayers amir dalal, Rafael Fernandes, Jonathan Ruhman Moire potentials in vdW bilayers have been recently extended from graphene to a variety of transition metal dichalcogenides (TMDs). In particular, correlated insulating states were observed in heterogeneous TMD bilayers. On the hole doped side the flat minibands are isolated from one another due to large spinorbit splittings. However, on the electron doped side these splittings tend to be much smaller allowing for a partial population of more than one flat band simultaneously. This opens an interesting path to study the interplay of itinerant and localized electrons in moire superlattices. 
Monday, March 15, 2021 5:00PM  5:12PM Live 
C41.00011: Generalized Wigner crystallization in moiré materials Bikash Padhi, Chitra Ramasubramanian, Philip Phillips Recent experiments on the twisted transition metal dichalcogenide (TMD) materials have observed insulating states at fractional occupancy of the moiré bands. Such states were conceived as generalized Wigner crystals (GWCs). In this article, we investigate the general problem of Wigner crystallization in the presence of an underlying (moiré) lattice. Based on the best estimates of the system parameters, we find a variety of homobilayer and heterobilayer TMDs to be excellent candidates for realizing GWCs. In particular, our analysis based on r_{s} indicates that MoSe_{2} (among the homobilayers) and MoSe_{2}/WSe_{2} or MoS_{2}/WS_{2} (among the heterobilayers) are the best candidates for realizing GWCs. We also establish that due to larger effective mass of the valence bands, in general, holecrystals are easier to realize that electroncrystals as seen experimentally. These crystals realized on a moiré lattice, unlike the conventional Wigner crystals, are incompressible due the gap arising from pinning with the lattice. Finally, we capture this manybody gap by variationally renormalizing the dispersion of the vibration modes. 
Monday, March 15, 2021 5:12PM  5:24PM Live 
C41.00012: Spectroscopy of Mn12 with modified ligands on graphene bolometers Luke St. Marie, Lubomir Havlicek, Jakub Hruby, Davonne Henry, Antonin Sojka, Jorge Navarro, Rachael L MyersWard, Abdel El Fatimy, Amy Liu, David Kurt Gaskill, Ivan Nemec, Petr Neugebauer, Paola Barbara Single molecule magnets (SMMs), metalion complexes that exhibit quantum behavior at low temperatures, have promising applications in quantum computing and molecular spintronics. The interfacial interactions between SMM ligands and surfaces can substantially alter the SMM properties. By combining SMMs with graphene, we can create hybrid materials with emergent properties that give them even greater potential. But graphene can also serve as a way to probe the properties of the SMMs. Graphene and SMM derivatives of Mn12 with modified CHCl2 carboxylate ligands have previously been combined to study the effects of charge transfer on the electronic transport properties of the decorated graphene^{[1]}. We combined these Mn12 derivatives with highly sensitive, ultrabroadband photodetectors fabricated from graphene^{[2]} to conduct electron paramagnetic resonance (EPR) spectroscopy of the SMMs. 
Monday, March 15, 2021 5:24PM  5:36PM Live 
C41.00013: Tunable Klein tunneling using Spin orbit coupling in a 2D EG Travis Rogowski, Godfrey Anthony Gumbs, Andrii Iurov, Danhong Huang Klein tunneling of particles across an electrostatic potential barrier has long been the phenomenon which has captivated both experimentalists and theorists for many years.We discuss the effect of the spinorbit interaction on the band structure, and wave functions in quasitwodimensional electron systems. We then use these states in the matching conditions across a sharp but atomically smooth electrostatic potential barrier to calculate the transmission probability. We employ this result for the tunneling probability in the LandauerButtiker formula to calculate the ballistic conductivity. Additionally, we investigate the conditions under which there is Klein tunneling at an angle other than when there is headon impact. 
Monday, March 15, 2021 5:36PM  5:48PM 
C41.00014: Coherent Lattice Wobbling and Dynamic Breaking of Friedel's Law Observed by Ultrafast Electron Diffraction Qingkai Qian, Xiaozhe Shen, Duan Luo, Xijie Wang, Shengxi Huang The inspection of Friedel's law in ultrafast electron diffraction (UED) is important to gain a comprehensive understanding of material atomic structure and its dynamic response. Here, monoclinic gallium telluride (GaTe), as a lowsymmetry, layered crystal in contrast to many other 2D materials, is investigated by megaelectronvolt UED. Strong outofphase oscillations of Bragg peak intensities are observed for Friedel pairs, which has dynamically violated the Friedel's law. As evidenced by the preserved mirror symmetry and supported by both kinematic and dynamic scattering simulations, the intensity oscillations are provoked by the lowestorder longitudinal acoustic breathing phonon. Our results provide a generalized understanding of Friedel's law in UED, and demonstrate that by designed misalignment of surface normal and primitive lattice vectors, coherent lattice wobbling and effective shear strain can be generated in crystal films by laser pulse excitation, which is otherwise hard to achieve and can be further utilized to dynamically tune and switch material properties. 
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