Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session D48: Quantum ManyBody Systems and Methods IRecordings Available

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Sponsoring Units: DCOMP Chair: Talat Rahman, University of Central Florida Room: McCormick Place W471A 
Monday, March 14, 2022 3:00PM  3:12PM 
D48.00001: Correlated Electron Dynamics in Finite Hubbard Clusters: Benchmarking the G1–G2 Scheme JanPhilip Joost, Hannes Ohldag, Niclas Schlünzen, Michael Bonitz The selfconsistent theoretical treatment of correlation and quantum effects beyond onedimensional systems is a particular challenge that has been successfully attacked with nonequilibrium Green functions (NEGF) methods [1]. However, NEGF simulations are hampered by a cubic scaling of the computation time with the number of time steps N_{t}. Recently, a dramatic acceleration has been achieved within the G1–G2 scheme [2] by transforming the NEGF equations, within the HartreeFock GKBA, to a time local form for the singleparticle and twoparticle Green functions. A detailed discussion of the method, its application to a variety of selfenergies including particleparticle and particlehole Tmatrix approximation, GW approximation, and dynamically screened ladder approximation was presented recently [3]. Here, we present extensive tests of the G1–G2 scheme within the screened ladder approximation for finite Hubbard clusters out of equilibrium. Stable simulations over long times are achieved by enforcing contraction consistency and by performing a purification of the dynamics [4]. 
Monday, March 14, 2022 3:12PM  3:24PM 
D48.00002: Magnetism and Mottness in the unfrustrated triangular lattice Hubbard model: a cellular dynamical meanfield study Marcel Klett, Michel Ferrero, Philipp Hansmann, Thomas Schaefer We investigate the phase diagram of the unfrustrated triangular lattice Hubbard model in a centerfocused cellular dynamical meanfield theory (CDMFT) approach using impurity clusters of 4, 7 and 19 sites [1,2]. We investigate the Mott metaltoinsulator transition and crossover region in terms of these cluster sizes. Using a magnetic symmetrybroken approach of the CDMFT, allowing for a rotations of spins on the Bloch sphere, we are able to investigate the magnetic ordering of the different cluster schemes. 
Monday, March 14, 2022 3:24PM  3:36PM 
D48.00003: Precise ground state of multiorbital Mott systems via the variational discrete action theory Zhengqian Cheng, Zhengqian Cheng, Chris Marianetti Determining the ground state of multiorbital Hubbard models is critical for understanding strongly correlated electron materials, yet existing methods struggle to reach zero temperature and infinite system size simultaneously. Even in infinite dimensions, the solution via the dynamical meanfield theory (DMFT) is limited by the absence of unbiased impurity solvers for zero temperature and multiple orbitals. The recently developed variational discrete action theory (VDAT) offers a new approach, with a variational ansatz that is controlled by an integer \mathcal{N}, and monotonically approaches the exact solution at an exponentially increasing computational cost. Here we implement VDAT for the multiorbital Hubbard model in d=\infty for \mathcal{N}=24. At \mathcal{N}=2, VDAT rigorously recovers the multiorbital Gutzwiller approximation, reproducing known results. At \mathcal{N}=3, VDAT qualitatively and quantitatively captures the competition between U, J, and the crystal field in the twoband Hubbard model, with a negligible computational cost. VDAT will have farranging implications for understanding strongly correlated materials. 
Monday, March 14, 2022 3:36PM  3:48PM 
D48.00004: Nonlocal correlations and criticality in the triangular lattice Hubbard model Mario M de Oliveira, Julian Stobbe, Marcel Klett, Georg Rohringer, Thomas Schaefer We investigate the role of nonlocal electronic correlations at finite temperatures in the halffilled triangular lattice Hubbard model using the dynamical vertex approximation (DΓA), a diagrammatic extension [1] of the dynamical meanfield theory (DMFT). We analyze the impact of (quantum) phase transitions on finite temperature properties at the one and twoparticle level. We discuss the absence of magnetic ordering at finite temperatures due to the fulfilment of the MerminWagner theorem and the (Mott) metalinsulator crossover. In addition we compare the results of this method to the ones obtained by other cuttingedge techniques like DMFT, its realspace cluster extension cellular dynamical meanfield theory (CDMFT) and diagrammatic Monte Carlo (DiagMC) [2]. 
Monday, March 14, 2022 3:48PM  4:00PM 
D48.00005: The Mott metalinsulator transition in the twodimensional Hubbard model  a cellular dynamical meanfield study on large clusters Michael D Meixner, Marcel Klett, Sarah Heinzelmann, Sabine Andergassen, Philipp Hansmann, Thomas Schaefer We study the halffilled twodimensional Hubbard model on a square lattice in cellular dynamical meanfield theory (CDMFT), a realspace cluster extension [1] of the dynamical meanfield theory. By increasing the number of cluster sites up to 6x6 we observe a progressive reduction of the onset interaction U* of a metalinsulator crossover. In particular, in the case of 4x4 sites, we observe a sitedependent U, which is lower at the center sites is lower than at the corner sites. In addition to this realspace analysis we investigate different periodization schemes for the oneparticle spectral function and argue that a centerfocused [2] cumulant scheme is wellsuited in the intermediate coupling regime of U due to its locality. 
Monday, March 14, 2022 4:00PM  4:12PM 
D48.00006: Controlled bond expansion for DMRG ground state search at singlesite costs Andreas Gleis, JhengWei Li, Jan Von Delft We present a controlled bond expansion (CBE) approach for ground state searches based on the density matrix renormalization group (DMRG) employing matrix product states (MPS). The main idea of CBEDMRG is as follows: Before optimizing the center tensor of an MPS in the site canonical form, the isometry on the next site is expanded by the most important contributions of its orthogonal complement. These contributions are determined by considering how the Hamiltonian acts on the current state. The accuracy of CBEDMRG is comparable to twosite DMRG, but its numerical costs scale like those of onesite DMRG. Moreover, in contrast to previous onesite methods involving bond expansion, it does not rely on any adhoc mixing parameters. Starting from an initial state with low bonddimension, the CBE prescription for increasing the bond dimension is controlled, automated and more economical than the manual adjustment typically used for twosite DMRG, leading to an additional significant speedup for reaching convergence. We illustrate the numerical performance of CBEDMRG with several examples of fermionic models, including free fermions on a chain for benchmarking and a Kondo lattice on a cylinder as a challenging application. 
Monday, March 14, 2022 4:12PM  4:24PM 
D48.00007: Timedependent variation principle with controlled bond expansion for matrix product states JhengWei Li, Andreas Gleis, Jan Von Delft We present a controlled bond expansion (CBE) approach to simulate quantum dynamics based on the timedependent variation principle (TDVP) for matrix product states (MPS). While the original singlesite TDVP integrator assumes a fixed bond dimension, CBETDVP starts with a small one and increases it on the fly as the entanglement entropy grows with time. To this end, CBE systematically introduces new subspaces, based on the isometry orthogonal to the TDVP tangent space which carries most weight in the projection error. CBE increases the bond dimension in an economical manner, and the truncation error sets in only once the bond dimension has reached a specified maximal value. Even beyond that time, the numerical accuracy remains wellcontrolled, being governed by the (growing) truncation error. CBETDVP is able to reach time scales comparable to any standard twosite algorithm, but without resorting to twosite update. Moreover, being based on TDVP, it can be used for longranged Hamiltonians. We illustrate its performance with several examples, including the oneaxis twisting model and the HaldaneShastry model for benchmark purposes, and polaron dynamics in the PeierlsHubbard model. 
Monday, March 14, 2022 4:24PM  4:36PM 
D48.00008: Computing Spectral functions of strongly correlated Hamiltonians using DMRG: rootN Krylov space approach for correctionvectors Alberto Nocera, Gonzalo Alvarez We propose a method to compute spectral functions of generic Hamiltonians using the density matrix renormalization group (DMRG) method directly in frequency space, based on a modified Krylov space approach to compute the correctionvectors. The approach entails the calculation of the rootN (N = 2 is the standard square root) of the Hamiltonian propagator using Krylov space decomposition, and repeating this procedure N times to obtain the actual correctionvector. Even though the approach still involves separate calculations for different target frequencies, we show that it greatly alleviates the burden of keeping a large bond dimension as in the standard correctionvector DMRG method, while achieving better computational performance at large N. Finally, we apply this approach to spin and charge spectral functions of tJ and Hubbard models in the challenging twoleg ladder geometry, showing that it also reaches a much improved resolution at large frequencies. 
Monday, March 14, 2022 4:36PM  4:48PM 
D48.00009: Energy twisted boundary condition Taozhi Guo, Ryota Nakai, Shinsei Ryu Thermal transport in condensed matter systems is traditionally formulated as a response to a background gravitational field. In this work, we seek a twisted boundary condition formalism for thermal transport in analog to the U(1) twisted boundary condition for electrical transport. We started by implementing the energy twisted boundary condition in CFT. Then using the transfer matrix method, we obtained the thermal Meissner stiffness of the Ising model and disordered Fermion model with energy twisted boundary condition. We also identified boost deformation for integrable systems as a similar formalism as energy twisted boundary condition and computed linear and nonlinear Drude weight for XXZ model. 
Monday, March 14, 2022 4:48PM  5:00PM 
D48.00010: Interplay of spinorbit coupling and nonlocal correlations with the TwoParticle SelfConsistent method Dominik Lessnich, Steffen Backes, Aleksandar Razpopov, Karim Zantout, Roser Valenti We show in which way it is possible to include spinorbit coupling (SOC) terms in the TwoParticle SelfConsistent method (TPSC). TPSC is a manybody method, valid for weak to intermediate interaction strength, which with moderate computational effort allows to investigate nonlocal correlation effects [Vilk, Tremblay J. Phys. I France, 7 11 (1997) 13091368]. Originally developed for singleband lattice models, in recent years TPSC was extended to the multiorbital case [Zantout et al., Phys. Rev. Lett. 123, 256401 (2019), Zantout et al., Annalen der Physik 2000399 (2021)]. Inclusion of SOC into TPSC is desirable to study systems in which the effects of SOC cannot be neglected as e.g. in Sr2RuO4 [Phys. Rev. Lett. 101, 026406 (2008)]. However, including SOC into TPSC is not straightforward since TPSC in its original formulation relies on spin rotational symmetry, a symmetry which is explicitly broken by SOC terms. We present key ideas which make this nevertheless possible and discuss the effect spinorbit coupling on the selfenergy and spin and charge correlation functions of interacting model systems. 
Monday, March 14, 2022 5:00PM  5:12PM 
D48.00011: Entanglement Entropy from Nonequilibrium Work Jonathan Demidio The Rényi entanglement entropy in quantum manybody systems can be viewed as the difference in free energy between partition functions with different trace topologies. We introduce an external field λ that controls the partition function topology, allowing us to define a notion of nonequilibrium work as λ is varied smoothly. Nonequilibrium fluctuation theorems of the work provide us with statistically exact estimates of the Rényi entanglement entropy. We use these ideas to extract universal information from quantum Monte Carlo simulations of spin models in one and two dimensions. The vast gain in efficiency of this method allows us to access unprecedented system sizes up to 192×96 spins for the square lattice Heisenberg antiferromagnet. 
Monday, March 14, 2022 5:12PM  5:24PM 
D48.00012: Rainbow Scars: From Area to Volume Law Christopher M Langlett, Shenglong Xu, Thomas Iadecola, Alexey V Gorshkov, Julia S Wildeboer, Zhicheng Yang Quantum manybody scars(QMBS) constitute a new quantum dynamical regime in which rare "scarred" eigenstates mediate weak ergodicity breaking. One open question is to understand the most general setting in which these states arise. In this work, we develop a generic construction that embeds a new class of QMBS, rainbow scars, into the spectrum of an arbitrary Hamiltonian. Unlike other examples of QMBS, rainbow scars display extensive bipartite entanglement entropy while retaining a simple entanglement structure. Specifically, the entanglement scaling is volumelaw for a random bipartition, while scaling for a finetuned bipartition is subextensive. When internal symmetries are present, the construction leads to multiple, and even towers of rainbow scars revealed through distinctive nonthermal dynamics. To this end, we provide an experimental road map for realizing rainbow scar states in a Rydbergatom quantum simulator, leading to coherent oscillations distinct from the strictly subvolumelaw QMBS previously realized in the same system. 
Monday, March 14, 2022 5:24PM  5:36PM 
D48.00013: Interactions and phonons derived from first principles using quantum Monte Carlo techniques Kevin G Kleiner, Lucas K Wagner There are many systems which possess strong interactions and lattice degrees of freedom including hightemperature superconductors [1] and color centers in semiconductors [2]. However, electronphonon models are typically derived within the framework of band structure, which leads to doublecounting issues when interactions are reintroduced, among other issues of accuracy. 
Monday, March 14, 2022 5:36PM  5:48PM 
D48.00014: Electronic excitations in correlated finite 2D materials generated by ion impact Michael Bonitz, Niclas Schluenzen, JanPhilip Joost, Lotte Amelie Borkowski, Karsten Balzer, Hannes Ohldag The impact of ions on solid targets is of high interest in many fields and has been extensively treated in linear response. However, ions give rise to a very strong, highly localized and fast excitation that my well lead to nonlinear and nonadiabatic effects. The ioninitiated dynamics are particularly interesting in strongly correlated materials giving rise to nontrivial electronic processes such as the excitation of doublons [1]. We present a timeresolved analysis of these processes in finite 2D graphenetype clusters, using a 
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