Emanuel Gull

University of Michigan–Ann Arbor

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Andrew J. Millis

Columbia University

Guy Cohen

Tel Aviv University

Matthias Troyer

Microsoft (United States)

Sergei Iskakov

University of Michigan–Ann Arbor

Dominika Zgid

University of Michigan–Ann Arbor

J. P. F. LeBlanc

Memorial University of Newfoundland

Philipp Werner

University of Fribourg

Andrey E. Antipov

Microsoft (United States)

Hiroshi Shinaoka

Saitama University

Markus Wallerberger

TU Wien

Cooperative Institutions

University of Michigan–Ann Arbor

University of Maryland, College Park

Sandia National Laboratories

ETH Zurich

Lawrence Berkeley National Laboratory

Robert Bosch (Germany)

ExxonMobil (United States)

RIKEN Center for Advanced Photonics

RIKEN Center for Quantum Computing

Centre National de la Recherche Scientifique

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Electron correlations in the cubic paramagnetic perovskite Sr(V,Mn)O3 : Results from fully self-consistent self-energy embedding calculations

Physical review. B./Physical review. B (2021)

Chia-Nan Yeh Sergei Iskakov Dominika Zgid Emanuel Gull

In this paper, we use the thermodynamically consistent and conserving self-energy embedding theory (SEET) to study the spectra of the prototypical undistorted cubic perovskites ${\mathrm{SrVO}}_{3}$ and ${\mathrm{SrMnO}}_{3}$. In the strongly correlated metallic ${\mathrm{SrVO}}_{3}$ we find that the usual attribution of the satellite peaks at --1.8 eV to Hund or Hubbard physics in the ${t}_{2g}$ orbitals is inconsistent with our calculations. In the strongly correlated insulator ${\mathrm{SrMnO}}_{3}$ we recover insulating behavior due to a feedback effect between the strongly correlated orbitals and the weakly correlated environment. Our calculation shows a systematic convergence of spectral features as the space of strongly correlated orbitals is enlarged, paving the way to a systematic parameter-free study of correlated perovskites.

10.1103/physrevb.103.195149

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Effect of propagator renormalization on the band gap of solids.

arXiv (Cornell University) (2018)

Sergei Iskakov Alexander A. Rusakov Dominika Zgid Emanuel Gull

We present momentum-resolved spectral functions and band gaps from bare and self-consistent second order perturbation theory for insulating periodic solids. We establish that, for systems with large gap sizes, both bare and self-consistent perturbation theory yield reasonable gaps. However, smaller gap sizes require a self-consistent adjustment of the propagator. In contrast to results obtained within a quasi-particle formalism used on top of bare second order perturbation theory, no unphysical behaviour of the band gap is observed. We establish that the renormalization or `screening' of interaction terms in addition to propagators is not required to obtain accurate gaps in insulators. Our implementation of a fully self-consistent, $\Phi$-derivable and thermodynamically consistent finite temperature diagrammatic perturbation theory forms a framework on which embedding theories such as the dynamical mean field theory or self-energy embedding theories can be implemented.

Propagator

Self-energy

Diagrammatic reasoning

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Opendf - An Implementation of the Dual Fermion Method for Strongly Correlated Systems

Physics Procedia (2015)

Andrey E. Antipov J. P. F. LeBlanc Emanuel Gull

The dual fermion method is a multiscale approach for solving lattice problems of interacting strongly correlated systems. In this paper, we present the \texttt{opendf} code, an open-source implementation of the dual fermion method applicable to fermionic single-orbital lattice models in dimensions $D=1,2,3$ and $4$. The method is built on a dynamical mean field starting point, which neglects all local correlations, and perturbatively adds spatial correlations. Our code is distributed as an open-source package under the GNU public license version 2.

Lattice (music)

Code (set theory)

10.1016/j.phpro.2015.07.107

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ALPSCore/ALPSCore: Version 2.3.0-rc.1

Alexander Gaenko Andrey E. Antipov Gabriele Carcassi Lukas Gamper Tianran Chen

10.5281/zenodo.1491799

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Green's functions from real-time bold-line Monte Carlo

Physical Review B (2014)

Guy Cohen David R. Reichman Andrew J. Millis Emanuel Gull

We present two methods for computing two-time correlation functions or Green's functions from real-time bold-line continuous-time quantum Monte Carlo. One method is a formally exact generalized auxiliary lead formalism by which spectral properties may be obtained from single-time observables. The other involves the evaluation of diagrams contributing to two-time observables directly on the Keldysh contour. Additionally, we provide a detailed description of the bold-line Monte Carlo method. Our methods are general and numerically exact, and able to reliably resolve high-energy features such as band edges. We compare the spectral functions obtained from real-time methods to analytically continued spectral functions obtained from imaginary-time Monte Carlo, thus probing the limits of analytic continuation.

Imaginary time

Formalism (music)

Monte Carlo integration

Quasi-Monte Carlo method

10.1103/physrevb.89.115139

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Citations (71)

Implementation of the bin hierarchy method for restoring a smooth function from a sampled histogram

Computer Physics Communications (2018)

Olga Goulko Alexander Gaenko Emanuel Gull Nikolay Prokof’ev Boris Svistunov

10.1016/j.cpc.2018.09.019

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Momentum-sector-selective metal-insulator transition in the eight-site dynamical mean-field approximation to the Hubbard model in two dimensions

Physical Review B (2009)

Emanuel Gull Olivier Parcollet Philipp Werner Andrew J. Millis

We explore the momentum-sector-selective metal-insulator transitions recently found in the eight-site dynamical cluster approximation to the two-dimensional Hubbard model. The phase diagram in the space of interaction and second-neighbor hopping is established. The initial transitions from Fermi-liquid-like to sector-selective phases are found to be of second order, caused by the continuous opening of an energy gap whereas the other transitions are found to be of first order. In the sector-selective phase the Fermi surface regions which are not gapped are found to have a non-Fermi-liquid self-energy. We demonstrate that the phenomenon is not caused by the Van Hove divergence in the density of states. The sector-selective and insulating phases are characterized by a cluster spin-correlation function that is strongly peaked at the commensurate antiferromagnetic wave vector $(\ensuremath{\pi},\ensuremath{\pi})$ but the model has no nematic instability. Comparison to dynamical mean-field studies on smaller clusters is made.

Mott insulator

Wave vector

Momentum (technical analysis)

Metal–insulator transition

10.1103/physrevb.80.245102

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Citations (105)

Magnetic and charge susceptibilities in the half-filled triangular lattice Hubbard model

Physical Review Research (2020)

Shaozhi Li Emanuel Gull

The authors provide theoretical results of the dynamic magnetic susceptibility in the triangular Hubbard model. They observe the low energy spin excitations at the K point persist in the transition from an insulator to a metal. This result is consistent with nuclear magnetic resonance observations on triangular compounds.

Hexagonal Lattice

10.1103/physrevresearch.2.013295

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Chirped amplitude mode in photo-excited superconductors

arXiv (Cornell University) (2024)

Thomas Blommel Jason Kaye Yuta Murakami Emanuel Gull Denis Golež

We show that the amplitude mode in superconductors exhibits chirped oscillations under resonant excitation and that the chirping velocity increases as we approach the critical excitation strength. The chirped amplitude mode enables us to determine the local modification of the effective potential even when the system is in a long-lived pre-thermal state. We then show that this chirped amplitude mode is an experimentally observable quantity since the photo-induced (super)-current in pump-probe experiments serves as an efficient proxy for the dynamics of the order parameter, including the chirped dynamics. Our result is based on the attractive Hubbard model using dynamical mean-field theory within the symmetry-broken state after a resonant excitation across the superconducting gap. Since the collective response takes place on emergently long timescales, we extend the hierarchical low-rank compression method for nonequilibrium Green's functions to symmetry-broken states and show that it serves as an efficient representation despite long-lived memory kernels.

Mode (computer interface)

10.48550/arxiv.2403.01589

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Heating and cooling in self-consistent many-body simulations

arXiv (Cornell University) (2023)

Yang Yu Sergei Iskakov Emanuel Gull

We present a temperature extrapolation technique for self-consistent many-body methods, which provides a causal starting point for converging to a solution at a target temperature. The technique employs the Carath\'eodory formalism for interpolating causal matrix-valued functions and is applicable to various many-body methods, including dynamical mean field theory, its cluster extensions, and self-consistent perturbative methods such as the self-consistent GW approximation. We show results that demonstrate that this technique can efficiently simulate heating and cooling hysteresis at a first-order phase transition, as well as accelerate convergence.

Formalism (music)

Self consistent

Hysteresis

10.48550/arxiv.2305.01452

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