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...

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 steady states and transient dynamics of conventional superconductors under phonon driving

Murakami, Yuta ; Tsuji, Naoto ; Eckstein, Martin ; Werner, Philipp

In: Physical Review B, 2017, vol. 96, no. 4, p. 045125

We perform a systematic analysis of the influence of phonon driving on the superconducting Holstein model coupled to heat baths by studying both the transient dynamics and the nonequilibrium steady state (NESS) in the weak and strong electron-phonon coupling regimes. Our study is based on the nonequilibrium dynamical mean-field theory, and for the NESS we present a Floquet formulation ...

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

Ultrafast switching of composite order in ${A}_{3}{\mathrm{C}}_{60}$

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

In: Physical Review B, 2017, vol. 95, no. 19, p. 195405

We study the controlled manipulation of the Jahn-Teller metal state of fulleride compounds using nonequilibrium dynamical mean-field theory. This anomalous metallic state is a spontaneous orbital-selective Mott phase, which is characterized by one metallic and two insulating orbitals. Using protocols based on transiently reduced hopping amplitudes or periodic electric fields, we demonstrate...

Université de Fribourg

Nonequilibrium dynamical cluster approximation study of the Falicov-Kimball model

Herrmann, Andreas J. ; Tsuji, Naoto ; Eckstein, Martin ; Werner, Philipp

In: Physical Review B, 2016, vol. 94, no. 24, p. 245114

We use a nonequilibrium implementation of the dynamical cluster approximation (DCA) to study the effect of short-range correlations on the dynamics of the two-dimensional Falicov-Kimball model after an interaction quench. As in the case of single-site dynamical mean-field theory, thermalization is absent in DCA simulations, and for quenches across the metal-insulator boundary,...