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

Comparative study of nonequilibrium insulator-to-metal transitions in electron-phonon systems

Sayyad, Sharareh ; Žitko, Rok ; Strand, Hugo U. R. ; Werner, Philipp ; Golež, Denis

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...

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...

Université de Fribourg

Ultrafast electronic band gap control in an excitonic insulator

Mor, Selene ; Herzog, Marc ; Golež, Denis ; Werner, Philipp ; Eckstein, Martin ; Katayama, Naoyuki ; Nohara, Minoru ; Takagi, Hide ; Mizokawa, Takashi ; Monney, Claude ; Stähler, Julia

In: Physical Review Letters, 2017, vol. 119, no. 8, p. 086401

We report on the nonequilibrium dynamics of the electronic structure of the layered semiconductor Ta2NiSe5 investigated by time- and angle-resolved photoelectron spectroscopy. We show that below the critical excitation density of FC=0.2 mJ cm−2, the band gap narrows transiently, while it is enhanced above FC. Hartree-Fock calculations reveal that this effect can be explained by the presence...

Université de Fribourg

Hund’s coupling driven photocarrier relaxation in the two-band Mott insulator

Strand, Hugo U. R. ; Golež, Denis ; Eckstein, Martin ; Werner, Philipp

In: Physical Review B, 2017, vol. 96, no. 16, p. 165104

We study the relaxation dynamics of photocarriers in the paramagnetic Mott insulating phase of the half-filled two-band Hubbard model. Using nonequilibrium dynamical mean-field theory, we excite charge carriers across the Mott gap by a short hopping modulation, and simulate the evolution of the photodoped population within the Hubbard bands. We observe an ultrafast charge-carrier relaxation...

Université de Fribourg

Nonequilibrium $GW+\mathrm{EDMFT}$: Antiscreening and Inverted Populations from Nonlocal Correlations

Golež, Denis ; Boehnke, Lewin ; Strand, Hugo U. R. ; Eckstein, Martin ; Werner, Philipp

In: Physical Review Letters, 2017, vol. 118, no. 24, p. 246402

We study the dynamics of screening in photodoped Mott insulators with long-ranged interactions using a nonequilibrium implementation of the GW plus extended dynamical mean-field theory formalism. Our study demonstrates that the complex interplay of the injected carriers with bosonic degrees of freedom (charge fluctuations) can result in long-lived transient states with properties that are...

Université de Fribourg

Photoinduced gap closure in an excitonic insulator

Golež, Denis ; Werner, Philipp ; Eckstein, Martin

In: Physical Review B, 2016, vol. 94, no. 3, p. 35121

We study the dynamical phase transition out of an excitonic insulator phase after photoexcitation using a time-dependent extension of the self-consistent GW method. We connect the evolution of the photoemission spectra to the dynamics of the excitonic order parameter and identify two dynamical phase transition points marked by a slowdown in the relaxation: one critical point is connected with...

Université de Fribourg

Dynamics of screening in photodoped Mott insulators

Golež, Denis ; Eckstein, Martin ; Werner, Philipp

In: Physical Review B, 2015, vol. 92, no. 19, p. 195123

We use a nonequilibrium implementation of extended dynamical mean-field theory in combination with a noncrossing approximation impurity solver to study the effect of dynamical screening in photoexcited Mott insulators. The insertion of doublons and holes adds low-energy screening modes and leads to a reduction of the Mott gap. The coupling to low-energy bosonic modes furthermore opens new...