Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session X50: Correlated 2D Materials and Models 
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Sponsoring Units: DCMP Chair: Shenglong Xu, University of Maryland, College Park Room: Mile High Ballroom 1C 
Friday, March 6, 2020 11:15AM  11:27AM 
X50.00001: Temperature dependence of the Mott gap in singlelayer 1TTaSe_{2} revealed by scanning tunneling spectroscopy Wei Ruan, Yi Chen, Jinwoong Hwang, Shujie Tang, Ryan Lee, HsinZon Tsai, Salman Abdul Gaffar Kahn, Franklin Liou, Andrew Aikawa, Zhixun Shen, SungKwan Mo, Michael F Crommie A key to unraveling the hightemperature superconductivity mechanism in cuprates is to understand the Metalinsulator transition in Mott insulators that can be induced by either doping charge or raising temperature. While the doping dependence of the Mott gap in cuprates has been studied extensively, it is difficult to explore the gap's temperature dependence in these systems due to its large size (typically 1~2 eV) and the resulting high temperature scale required to melt the Mottstate. Here we use scanning tunneling microscopy/spectroscopy to investigate the temperature dependence of the electronic structure of the singlelayer Mott insulator 1TTaSe_{2} which has a much more modest Mott gap of ~ 0.1 eV. We observe that the gap closes rapidly at a temperature scale that is significantly smaller than the gap size. This is accompanied by changes in the exotic orbital texture of the upper Hubbard band that are consistent with reduced screening at elevated temperatures. This phenomenon is unique among strongly correlated systems and is compatible with recent theoretical predictions where spin fluctuations are responsible for the rapid gap closing. 
Friday, March 6, 2020 11:27AM  11:39AM 
X50.00002: Manipulation of electronphonon energy transfer pathways in 2D transition metal dichalcogenides through ultrafast excitation Emma CatingSubramanian, Christian Gentry, Xun Shi, Yingchao Zhang, Wenjing You, Sinead Ryan, Baldwin Akin Varner, Kai Rossnagel, Henry Kapteyn, Margaret Murnane The complex phase landscape of quantum materials provides tremendous opportunity for design, manipulation, and coherent control of material properties using light. Understanding that complexity also poses a significant challenge, and multiple techniques are needed to map and exploit the rich phase space of strongly correlated materials. For example, using ultrafast electron calorimetry via time and angleresolved photoemission (ARPES), a bidirectional energy transfer between stronglycorrelated electron and phonon modes in a material has been observed for the first time  in this case a charge density wave (CDW) material 1TTaSe_{2}. 
Friday, March 6, 2020 11:39AM  11:51AM 
X50.00003: Negative Parabolic Magnetoresistance in a strongly interacting 2D Hole system in GaAs/AlGaAs Arvind Shankar Kumar, ChiehWen Liu, Shuhao Liu, Loren Pfeiffer, Kenneth West, Xuan Gao Electronelectron interactions are believed to be an important factor in the origin of the 2D MetalInsulator Transition observed in strongly correlated 2D electron/hole systems. In the weakly interacting (Fermi Liquid) regime, these interactions can be shown to cause a negative parabolic correction to the magnetoresistance of the 2D electron/hole system. We observe a similar magnetoresistance effect in the strong field regime (ω_{c}τ > 1) for a strongly interacting 2D hole liquid (r_{s}=2030) in a GaAs/AlGaAs quantum well at low temperatures (T =0.09  1 K), in a hole density range (p=0.981.98 *10^{10} /cm^{2}) close to the critical density for the 2D MetalInsulator transition, where the temperature dependence of resistivity is nonmonotonic. We study the extracted holehole interaction correction to Drude conductivity in this regime and compare its temperature dependence to conventional Fermi Liquid theories. This study gives insight on the validity of a Fermi Liquid picture in the strongly interacting regime and explores whether this conventional picture of interacting electron systems can be used to explain the origin of the 2D metallic state. 
Friday, March 6, 2020 11:51AM  12:03PM 
X50.00004: Theory of Strain Effects on
Extremely Correlated Metals in Twodimensions Michael Arciniaga, Peizhi Mai, B Sriram Shastry We study the strain dependence of anisotropic resistivity [1] within the tt'J model, applicable to cuprate superconductors. This model is treated using the recently developed extremely correlated Fermi liquid theory (ECFL). We obtain the temperature, density and strain dependence of the anisotropic resistivity. We compute the strain response functions in different geometries for comparing with planned experiments [1]. We also study the strain dependence of the optical weight and the local density of states (LDOS) at low T. Our results provide quantitative predictions of these quantities for experimental tests on strongly correlated materials such as highTc materials. 
Friday, March 6, 2020 12:03PM  12:15PM 
X50.00005: Construction and classification of point group symmetry protected topological phases in 2D interacting fermionic systems Jianhao Zhang, QingRui Wang, Shuo Yang, Yang Qi, Zhengcheng Gu The construction and classification of symmetry protected topological (SPT) phases in interacting bosonic and fermionic systems have been intensively studied in the past few years. Very recently, a complete classification and construction of space group SPT phases were also proposed for interacting bosonic systems. In this paper, we attempt to generalize this classification and construction scheme into interacting fermion systems systematically. In particular, we construct and classify point group SPT phases for 2D interacting fermion systems via lowerdimensional blockstate decorations. We discover several intriguing fermionic SPT states that can only be realized in interacting fermion systems (i.e., no freefermion and bosonic SPT realizations). Moreover, we also verify the recently conjectured crystalline equivalence principle for 2D interacting fermion systems. Finally, a potential experimental realization of these new classes of point group SPT phases in 2D correlated superconductors is also addressed. 
Friday, March 6, 2020 12:15PM  12:27PM 
X50.00006: The NonGaussian Exact Diagonalization Method and Its Application to the 2D HubbardHolstein Model Yao Wang, Ilya Esterlis, Tao Shi, Juan Ignacio Cirac, Eugene Demler We propose a novel numerical method that embeds the variational nonGaussian wavefunction approach with exact diagonalization, allowing for efficient treatment of correlated systems with both electronelectron and electronphonon interactions. Using a generalized polaron transformation, we construct a variational wavefunction that minimizes the entanglement between electrons and phonons; exact diagonalization is then used to treat the electronic part of the wavefunction exactly, thus taking into account highorder correlation effects beyond the Gaussian level. Keeping the full electronic Hilbert space, the complexity is increased only by a polynomial factor relative to the exact diagonalization calculation for pure electrons. As an example, we use this method to study groundstate properties of the twodimensional HubbardHolstein model, providing evidence for the existence of intervening phases between the spin and chargeordered states. 
Friday, March 6, 2020 12:27PM  12:39PM 
X50.00007: Electromagnetic duality in 2D topological orders with gapped boundaries Hongyu Wang, Yingcheng Li, Yuting Hu, Yidun Wan We generalize the Electromagnetic (EM) duality and the mapping to the LevinWen (LW) model of the quantum double (QD) model to the case of topological orders with gapped boundaries. To achieve our goal, we Fourier transform the extended QD model defined on the lattice with boundaries. The input data of the model is finite group $G$ and the boundary condition is characterized by subgroup $K \subseteq G$. After the Fourier transform, we find while the bulk degrees of freedom become $\rep_G$, the boundary condition is now characterized by Frobenius algebra $(\mathds{C}[G]/\mathds{C}[K])^*$, the quotient of the group algebra of $G$ over that of $K$. We also show that our Fouriertransformed extended QD model can be mapped to an extended LW model on the same lattice via enlarging the Hilbert space of the extended LW model. Moreover, our Fourier transform of the extended QD model provides a visualizable explanation of the phenomenon of splitting and partial condensation of anyons. 
Friday, March 6, 2020 12:39PM  12:51PM 
X50.00008: Catastrophe theory classification of Fermi surface topological transitions in two dimensions Anirudh Chandrasekaran, Oleksandr Shtyk, Joseph Betouras, Claudio Chamon We classify all possible singularities in the electronic dispersion of twodimensional systems that occur when the Fermi surface changes topology, using catastrophe theory. For systems with up to seven control parameters (i.e., pressure, strain, bias voltage, etc), the theory guarantees that the singularity belongs to to one of seventeen standard types. We show that at each of these singularities the density of states diverges as a power law, with a universal exponent characteristic of the particular catastrophe, and we provide its universal ratio of amplitudes of the prefactors of energies above and below the singularity. We further show that crystal symmetry restricts which types of catastrophes can occur at the points of high symmetry in the Brillouin zone. For each of the seventeen wallpaper groups in twodimensions, we can list which catastrophes are possible at each high symmetry point. 
Friday, March 6, 2020 12:51PM  1:03PM 
X50.00009: Symmetry protected longlived excitations and tomographic dynamics in 2D electron fluids Patrick Ledwith, Haoyu Guo, Leonid Levitov We will discuss the peculiar collective behavior in twodimensional Fermi gases arising from headon carriercarrier collisions. These collisions dominate at cold temperatures, T << T_{F}, due to the combined effects of Pauli blocking and momentum conservation. Oddparity harmonics are protected from these collisions and hence have anomalously long lifetimes. They instead slowly relax via small angle scattering which leads to a strange "superdiffusive" behavior. These longlived modes give rise to a "tomographic" transport regime dominated by fermionic jets with an unusual hierarchy of time scales and scaledependent transport coefficients with nontrivial fractional scaling dimensions. We will also discuss proposals for experimental realizations and implications for ongoing studies of electron hydrodynamics. 
Friday, March 6, 2020 1:03PM  1:15PM 
X50.00010: Hydrodynamic electron flow in 2D semiconductor heterostructures Aydin Keser, Daisy Qingwen Wang, Oleh Klochan, Derek Ho Yew Hung, Shaffique Adam, Dimitrie Culcer, Alex Hamilton, Oleg Sushkov We propose simple geometries to directly test hydrodynamic flow in 2D electron systems by longitudinal resistance measurements. We model the boundaries of the electron fluid as `slippery', i.e. supporting no longitudinal stress, hence, we show that the viscous component of resistance depends significantly on the geometric features while it vanishes along the straight featureless sections. Moreover, since the viscous resistance increases quadratically with the inverse scale of the system, we show that channels in which the viscous and Ohmic effects are comparable can be manufactured with current technology. Elementary, bent or nozzle/diffuser type channels show significant departure from their diffusive counterparts in the hydrodynamic regime. 
Friday, March 6, 2020 1:15PM  1:27PM 
X50.00011: Atypical Behavior of Collective Modes in TwoDimensional Fermi Liquids Matthew Gochan, Joshuah Timothy Heath, Kevin Shawn Bedell Since its development by L.V. Landau sixty years ago, Fermi liquid theory continues to serve as a formidable model for interacting Fermi systems in addition to providing the standard which all other models are held to. Of the numerous accomplishments of Fermi liquid theory, the calculation of various transport properties is of particular interest. In this talk we apply the Landau kinetic equation to a twodimensional Fermi liquid and discuss the consequences of the reduced dimensionality on the behavior of the collective modes. As a function of the usual dimensionless parameter s = ω/v_{F}, we find expected behavior in addition to new results for the behavior of the zero sound mode c_{0}. Additionally, we investigate the effect of a Coulomb interaction on the system resulting in an expression for plasmon frequency ω_{p} in 2D with a crossover as a function of q to the zero sound mode. 
Friday, March 6, 2020 1:27PM  1:39PM 
X50.00012: A determinantal quantum Monte Carlo study of deconfined quantum criticality Chao Wang, Yoni Schattner, Steven Kivelson We study an interacting electrondimer model on the square lattice using the determinantal quantum Monte Carlo technique. We present evidence for a deconfined quantum critical point between antiferromagnetic and columnar valencebond solid phases and examine the properties of the critical point. 
Friday, March 6, 2020 1:39PM  1:51PM 
X50.00013: Metal insulator transition induced by magnetic field in GdTe Xinqiang Cai, Zhilin Xu, Zuoping Zhou, Wantong Huang, Shuaihua Ji, Xi Chen

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