Université de Fribourg

NESSi : The Non-Equilibrium Systems Simulation package

Schüler, Michael ; Golež, Denis ; Murakami, Yuta ; Bittner, Nikolaj ; Herrmann, Andreas ; U.R.Strand, Hugo ; Werner, Philipp ; Eckstein, Martin

In: Computer Physics Communications, 2020, vol. 257, no. 2020, p. 107484

The nonequilibrium dynamics of correlated many-particle systems is of interest in connection with pump–probe experiments on molecular systems and solids, as well as theoretical investigations of transport properties and relaxation processes. Nonequilibrium Green’s functions are a powerful tool to study interaction effects in quantum many-particle systems out of equilibrium, and to extract...

Université de Fribourg

How circular dichroism in time- and angle-resolved photoemission can be used to spectroscopically detect transient topological states in graphene

Schüler, Michael ; Giovannini, Umberto De ; Hübener, Hannes ; Rubio, Angel ; Sentef, Michael A. ; Devereaux, Thomas P. ; Werner, Philipp

In: Physical Review X, 2020, vol. 10, no. 4, p. 041013

Pumping graphene with circularly polarized light is the archetype of light-tailoring topological bands. Realizing the induced Floquet-Chern-insulator state and demonstrating clear experimental evidence for its topological nature has been a challenge, and it has become clear that scattering effects play a crucial role. We tackle this gap between theory and experiment by employing microscopic...

Université de Fribourg

High-harmonic generation in spin-orbit coupled systems

Lysne, Markus ; Murakami, Yuta ; Schüler, Michael ; Werner, Philipp

In: Physical Review B, 2020, vol. 102, no. 8, p. 081121

We study high-harmonic generation in two-dimensional electron systems with Rashba and Dresselhaus spin-orbit coupling and derive harmonic generation selection rules with the help of group theory. Based on the band structures of these minimal models and explicit simulations we reveal how the spin-orbit parameters control the cutoff energy in the high-harmonic spectrum. We also show that the...

Université de Fribourg

Local Berry curvature signatures in dichroic angle-resolved photoelectron spectroscopy from two-dimensional materials

Schüler, Michael ; Giovannini, Umberto De ; Hübener, Hannes ; Rubio, Angel ; Sentef, Michael A. ; Werner, Philipp

In: Science Advances, 2020, vol. 6, no. 9, p. eaay2730

Topologically nontrivial two-dimensional materials hold great promise for next- generation optoelectronic applications. However, measuring the Hall or spin-Hall response is often a challenge and practically limited to the ground state. An experimental technique for tracing the topological character in a differential fashion would provide useful insights. In this work, we show that circular...

Université de Fribourg

Ultrafast nonequilibrium evolution of excitonic modes in semiconductors

Murakami, Yuta ; Schüler, Michael ; Takayoshi, Shintaro ; Werner, Philipp

In: Physical Review B, 2020, vol. 101, no. 3, p. 035203

We study the time evolution of excitonic states after photoexcitation in the one- dimensional spinless extended Falicov-Kimball model. Several numerical methods are employed and benchmarked against each other: time-dependent mean-field simulations, the second-Born approximation (2BA) within the Kadanoff-Baym formalism, the generalized Kadanoff-Baym ansatz (GKBA) implemented with the 2BA, and...

Université de Fribourg

From chaos to many-body localization: some introductory notes

Chotorlishvili, L. ; Stagraczyński, S. ; Schüler, Michael ; Berakdar, J.

In: Acta Physica Polonica A, 2019, vol. 135, no. 6, p. 1155–1162

Staring from the kicked rotator as a paradigm for a system exhibiting classical chaos, we discuss the role of quantum coherence resulting in dynamical localization in the kicked quantum rotator. In this context, the disorder-induced Anderson localization is also discussed. Localization in interacting, quantum many-body systems (many-body localization) may also occur in the absence of...

Université de Fribourg

Quench dynamics and Hall response of interacting Chern insulators

Schüler, Michael ; Budich, Jan Carl ; Werner, Philipp

In: Physical Review B, 2019, vol. 100, no. 4, p. 041101

We study the coherent nonequilibrium dynamics of interacting two-dimensional systems after a quench from a trivial to a topological Chern insulator phase. While the many-body wave function is constrained to remain topologically trivial under local unitary evolution, we find that the Hall response of the system can dynamically approach a thermal value of the postquench Hamiltonian, even though...

Université de Fribourg

Adiabatic preparation of a correlated symmetry‐broken initial state with the generalized Kadanoff–Baym Ansatz

Tuovinen, Riku ; Golež, Denis ; Schüler, Michael ; Werner, Philipp ; Eckstein, Martin ; Sentef, Michael A.

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...

Université de Fribourg

Truncating the memory time in nonequilibrium dynamical mean field theory calculations

Schüler, Michael ; Eckstein, Martin ; Werner, Philipp

In: Physical Review B, 2018, vol. 97, no. 24, p. 245129

The nonequilibrium Green's functions (NEGF) approach is a versatile theoretical tool, which allows to describe the electronic structure, spectroscopy, and dynamics of strongly correlated systems. The applicability of this method is, however, limited by its considerable computational cost. Due to the treatment of the full two-time dependence of the NEGF, the underlying equations of motion...

Université de Fribourg

Nonthermal switching of charge order: Dynamical slowing down and optimal control

Schüler, Michael ; Murakami, Yuta ; Werner, Philipp

In: Physical Review B, 2018, vol. 97, no. 15, p. 155136

We investigate the laser-induced dynamics of electronically driven charge-density- wave (CDW) order. A comprehensive mean-field analysis of the attractive Hubbard model in the weak-coupling regime reveals ultrafast switching and ultrafast melting of the order via a nonthermal pathway. The resulting nonequilibrium phase diagram exhibits multiple distinct regimes of the order parameter dynamics...