Université de Fribourg

Dynamics of photodoped charge transfer insulators

Golež, Denis ; Boehnke, Lewin ; Eckstein, Martin ; Werner, Philipp

In: Physical Review B, 2019, vol. 100, no. 4, p. 041111

We study the dynamics of charge transfer insulators after photoexcitation using the three-band Emery model and a nonequilibrium extension of Hartree-Fock + EDMFT (extended dynamical mean field theory) and GW + EDMFT. While the equilibrium properties are accurately reproduced by the Hartree-Fock treatment of the ligand bands, dynamical correlations are essential for a proper description of the...

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

Theory of photoinduced ultrafast switching to a spin-orbital ordered hidden phase

Li, Jiajun ; Strand, Hugo U.R. ; Werner, Philipp ; Eckstein, Martin

In: Nature Communications, 2018, vol. 9, no. 1, p. 4581

Photo-induced hidden phases are often observed in materials with intertwined orders. Understanding the formation of these non-thermal phases is challenging and requires a resolution of the cooperative interplay between different orders on the ultra-short timescale. In this work, we demonstrate that non-equilibrium photo-excitations can induce a state with spin-orbital orders entirely...

Université de Fribourg

Quantum Boltzmann equation for strongly correlated systems: Comparison to dynamical mean field theory

Wais, Michael ; Eckstein, Martin ; Fischer, R. ; Werner, Philipp ; Battiato, M. ; Held, K.

In: Physical Review B, 2018, vol. 98, no. 13, p. 134312

We investigate the potential of a quantum Boltzmann equation without momentum conservation for description of strongly correlated electron systems out of equilibrium. In a spirit similar to dynamical mean field theory (DMFT), the momentum conservation of the electron-electron scattering is neglected, which yields a time-dependent occupation function for the equilibrium spectral function, even...

Université de Fribourg

High-harmonic generation in Mott insulators

Murakami, Yuta ; Eckstein, Martin ; Werner, Philipp

In: Physical Review Letters, 2018, vol. 121, no. 5, p. 057405

Using Floquet dynamical mean-field theory, we study the high-harmonic generation in the time-periodic steady states of wide-gap Mott insulators under ac driving. In the strong-field regime, the harmonic intensity exhibits multiple plateaus, whose cutoff energies εcut=U+mE0 scale with the Coulomb interaction U and the maximum field strength E0. In this regime, the created doublons and holons...

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

Ultrafast doublon dynamics in photoexcited $1T$-${\mathrm{TaS}}_{2}$

Ligges, M. ; Avigo, I. ; Gole?, Denis ; Strand, H. ?U.? R. ; Beyazit, Y. ; Hanff, K. ; Diekmann, F. ; Stojchevska, L. ; Kalläne, M. ; Zhou, P. ; Rossnagel, K. ; Eckstein, Martin ; Werner, Philipp ; Bovensiepen, U.

In: Physical Review Letters, 2018, vol. 120, no. 16, p. 166401

Strongly correlated materials exhibit intriguing properties caused by intertwined microscopic interactions that are hard to disentangle in equilibrium. Employing nonequilibrium time-resolved photoemission spectroscopy on the quasi-two- dimensional transition-metal dichalcogenide 1T-TaS2, we identify a spectroscopic signature of doubly occupied sites (doublons) that reflects fundamental Mott...

Université de Fribourg

Enhanced pairing susceptibility in a photodoped two-orbital Hubbard model

Werner, Philipp ; Strand, Hugo U. R. ; Hoshino, Shintaro ; Murakami, Yuta ; Eckstein, Martin

In: Physical Review B, 2018, vol. 97, no. 16, p. 165119

Local spin fluctuations provide the glue for orbital-singlet spin-triplet pairing in the doped Mott insulating regime of multiorbital Hubbard models. At large Hubbard repulsion U, the pairing susceptibility is nevertheless tiny because the pairing interaction cannot overcome the suppression of charge fluctuations. Using nonequilibrium dynamical mean field simulations of the two-orbital...

Université de Fribourg

Floquet prethermalization in the resonantly driven Hubbard model

Herrmann, Andreas ; Murakami, Yuta ; Eckstein, Martin ; Werner, Philipp

In: EPL (Europhysics Letters), 2017, vol. 120, no. 5, p. 57001

We demonstrate the existence of long-lived prethermalized states in the Mott insulating Hubbard model driven by periodic electric fields. These states, which also exist in the resonantly driven case with a large density of photo-induced doublons and holons, are characterized by a nonzero current and an effective temperature of the doublons and holons which depends sensitively on the driving...

Université de Fribourg

Photoinduced enhancement of excitonic order

Murakami, Yuta ; Golež, Denis ; Eckstein, Martin ; Werner, Philipp

In: Physical Review Letters, 2017, vol. 119, no. 24, p. 247601

We study the dynamics of excitonic insulators coupled to phonons using the time- dependent mean-field theory. Without phonon couplings, the linear response is given by the damped amplitude oscillations of the order parameter with a frequency equal to the minimum band gap. A phonon coupling to the interband transfer integral induces two types of long-lived collective oscillations of the...