In: Physical Review B, 2015, vol. 91, no. 24, p. 245156
We study the reliability of the constrained random-phase approximation (cRPA) method for the calculation of low-energy effective Hamiltonians by considering multiorbital lattice models with one strongly correlated “target” band and two weakly correlated “screening” bands. The full multiorbital system and the effective model are solved within dynamical mean-field theory (DMFT) in a...
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In: physica status solidi (b), 2019, vol. 256, no. 7, p. 1800469
A fast time propagation method for nonequilibrium Green's functions (NEGF) based on the generalized Kadanoff–Baym Ansatz (GKBA) is applied to a lattice system with a symmetry‐broken equilibrium phase, namely an excitonic insulator (EI). The adiabatic preparation of a correlated symmetry‐broken initial state from a Hartree– Fock wave function within GKBA is assessed by comparing with a...
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In: Physical Review B, 2020, vol. 101, no. 4, p. 045108
We present a strategy to alleviate the sign problem in continuous-time quantum Monte Carlo (CTQMC) simulations of the dynamical-mean-field-theory (DMFT) equations for the spin-orbit-coupled multiorbital Hubbard model. We first identify the combinations of rotationally invariant Hund coupling terms present in the relativistic basis which lead to a severe sign problem. Exploiting the fact that...
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In: Physical Review B, 2017, vol. 96, no. 5, p. 054431
We derive the reciprocal cluster mean-field method to study the strongly interacting bosonic Harper-Hofstadter-Mott model. The system exhibits a rich phase diagram featuring band insulating, striped superfluid, and supersolid phases. Furthermore, for finite hopping anisotropy, we observe gapless uncondensed liquid phases at integer fillings, which are analyzed by exact diagonalization. The...
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In: Physical Review A, 2015, vol. 92, no. 6, p. 063602
We investigate features in the single-particle spectral function beyond the Hubbard bands in the strongly correlated normal phase of the Bose-Hubbard model. There are two distinct classes of additional peaks generated by the bosonic statistics. The first type is thermally activated Hubbard “sidebands”, with the same physical origin as the zero-temperature Hubbard bands, but generated by...
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In: Physical Review B, 2016, vol. 94, no. 19, p. 195119
We derive the self-energy functional theory for bosonic lattice systems with broken U(1) symmetry by parametrizing the bosonic Baym-Kadanoff effective action in terms of one- and two-point self-energies. The formalism goes beyond other approximate methods such as the pseudoparticle variational cluster approximation, the cluster composite boson mapping, and the Bogoliubov+U theory. It...
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In: Physical Review B, 2020, vol. 101, no. 19, p. 195118
We consider a two-band spinless model describing an excitonic insulator (EI) on the two-dimensional square lattice with anisotropic hopping parameters and electron-phonon (el-ph) coupling, inspired by the EI candidate Ta2NiSe5. We systematically study the nature of the collective excitations in the ordered phase which originates from the interband Coulomb interaction and the el-ph coupling. ...
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In: Physical Review B, 2019, vol. 99, no. 4, p. 045118
We study equilibrium and nonequilibrium properties of electron-phonon systems described by the Hubbard-Holstein model using dynamical mean-field theory. In equilibrium, we benchmark the results for impurity solvers based on the one-crossing approximation and slave-rotor approximation against non-perturbative numerical renormalization group reference data. We also examine how well the...
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In: Proceedings of Computational Science Workshop 2014 (CSW2014), 2015, vol. 5, p. -
We describe an implementation of the GW+DMFT method and apply it to calculate the electronic structure of SrVO₃. Our results show that there is a strong competition between the frequency-dependent Hubbard U and the non-local self-energy via the GW approximation. It is crucial to take into account these two aspects in order to obtain an accurate and coherent picture of the...
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In: Computer Physics Communications, 2017, vol. 215, p. 128–136
We describe an open-source implementation of the continuous-time hybridization- expansion quantum Monte Carlo method for impurity models with general instantaneous two-body interactions and complex hybridization functions. The code is built on an updated version of the core libraries of ALPS (Applications and Libraries for Physics Simulations) [ALPSCore libraries].
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