Université de Fribourg

Out-of-time-ordered correlators of the Hubbard model: Sachdev-Ye-Kitaev strange metal in the spin-freezing crossover region

Tsuji, Naoto ; Werner, Philipp

In: Physical Review B, 2019, vol. 99, no. 11, p. 115132

The Sachdev-Ye-Kitaev (SYK) model describes a strange metal that shows peculiar non-Fermi-liquid properties without quasiparticles. It exhibits a maximally chaotic behavior characterized by out-of-time-ordered correlators (OTOCs), and is expected to be a holographic dual to black holes. While a faithful realization of the SYK model in condensed-matter systems may be involved, a striking...

Université de Fribourg

Staggered ordered phases in the three-orbital Hubbard model

Ishigaki, Kosuke ; Nasu, Joji ; Koga, Akihisa ; Hoshino, Shintaro ; Werner, Philipp

In: Physical Review B, 2019, vol. 99, no. 8, p. 085131

We study ordered phases with broken translational symmetry in the half-filled three- orbital Hubbard model with antiferromagnetic Hund coupling by means of dynamical mean-field theory (DMFT) and continuous-time quantum Monte Carlo simulations. The stability regions of the antiferro-orbital (AFO), antiferromagnetic (AFM), and charge density wave (CDW) states are determined by measuring the...

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

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

Spin-freezing and the Sachdev-Ye model

Werner, Philipp ; Kim, Aaram J. ; Hoshino, Shintaro

In: EPL (Europhysics Letters), 2018, vol. 124, no. 5, p. 57002

Spin-freezing is the origin of bad-metal physics and non-Fermi liquid (non-FL) properties in a broad range of correlated compounds. In a multi-orbital lattice system with Hund coupling, doping of the half-filled Mott insulator results in a highly incoherent metal with frozen magnetic moments. These moments fluctuate and collapse in a crossover region that is characterized by unusual non-Fermi...

Université de Fribourg

Spontaneously orbital-selective superconductivity in a three-orbital Hubbard model

Ishigaki, Kosuke ; Nasu, Joji ; Koga, Akihisa ; Hoshino, Shintaro ; Werner, Philipp

In: Physical Review B, 2018, vol. 98, no. 23, p. 235120

We study a three-orbital Hubbard model with negative Hund's coupling in infinite dimensions, combining dynamical mean-field theory with continuous time quantum Monte Carlo simulations. This model, which is relevant for the description of alkali- doped fullerides, has previously been shown to exhibit a spontaneous orbital-selective Mott phase in the vicinity of the superconducting phase....

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

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

Linear behavior of the optical conductivity and incoherent charge transport in ${\mathrm{BaCoS}}_{2}$

Santos-Cottin, D. ; Klein, Y. ; Werner, Philipp ; Miyake, Takashi ; Medici, L. de ; Gauzzi, A. ; Lobo, R. P. S. M. ; Casula, Michele

In: Physical Review Materials, 2018, vol. 2, no. 10, p. 105001

Optical conductivity measurements on a BaCoS2 single crystal unveil an unusual linear behavior over a broad spectral range. In the paramagnetic phase above 300 K, the spectrum shows no gap, which contradicts the previously proposed scenario of a charge-transfer Mott insulator. Ab initio dynamical mean field theory calculations including a retarded Hubbard interaction explain the data in terms...

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...