Université de Fribourg

High-harmonic generation in quantum spin systems

Takayoshi, Shintaro ; Murakami, Yuta ; Werner, Philipp

In: Physical Review B, 2019, vol. 99, no. 18, p. 184303

We theoretically study the high-harmonic generation (HHG) in one-dimensional spin systems. While in electronic systems the driving by ac electric fields produces radiation from the dynamics of excited charges, we consider here the situation where spin systems excited by a magnetic field pulse generate radiation via a time- dependent magnetization. Specifically, we study the magnetic dipole...

Université de Fribourg

Nonequilibrium steady states of electric field driven Mott insulators

Murakami, Yuta ; Werner, Philipp

In: Physical Review B, 2018, vol. 98, no. 7, p. 075102

We present a systematic study of the nonequilibrium steady states (NESS) in Mott insulators driven by dc or ac electric fields, based on the Floquet dynamical mean- field theory. The results are analyzed using a generalized tunneling formula for the current, which is reminiscent of the Meir-Wingreen formula and provides insights into the relevant physical processes. In the dc case, the...

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

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...

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

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

Damping of the collective amplitude mode in superconductors with strong electron-phonon coupling

Murakami, Yuta ; Werner, Philipp ; Tsuji, Naoto ; Aoki, Hideo

In: Physical Review B, 2016, vol. 94, no. 11, p. 115126

We study the effect of strong electron-phonon interactions on the damping of the Higgs amplitude mode in superconductors by means of nonequilibrium dynamical mean-field simulations of the Holstein model. In contrast to the BCS dynamics, we find that the damping of the Higgs mode strongly depends on the temperature, becoming faster as the system approaches the transition temperature. The...

Université de Fribourg

Multiple amplitude modes in strongly coupled phonon-mediated superconductors

Murakami, Yuta ; Werner, Philipp ; Tsuji, Naoto ; Aoki, Hideo

In: Physical Review B, 2016, vol. 93, no. 9, p. 94509

We study collective amplitude modes of the superconducting order parameter in strongly coupled electron-phonon systems described by the Holstein model using the nonequilibrium dynamical mean-field theory with the self-consistent Migdal approximation as an impurity solver. The frequency of the Higgs amplitude mode is found to coincide with the superconducting gap even in the strongly coupled...