Université de Fribourg

Unconventional orbital ordering and emergent dimensional reduction in fulleride superconductors

Hoshino, Shintaro ; Werner, Philipp ; Arita, Ryotaro

In: Physical Review B, 2019, vol. 99, no. 23, p. 235133

Nonlocal order parameters in space-time are proposed to characterize the unconventional orbital-selective conducting state in fulleride superconductors, called the Jahn-Teller metal. In previous works, it has been argued that this state can be interpreted as a spontaneous orbital-selective Mott state, in which the electrons in two of the three t1u molecular orbitals are localized, while those...

Université de Fribourg

Quench dynamics and Hall response of interacting Chern insulators

Schüler, Michael ; Budich, Jan Carl ; Werner, Philipp

In: Physical Review B, 2019, vol. 100, no. 4, p. 041101

We study the coherent nonequilibrium dynamics of interacting two-dimensional systems after a quench from a trivial to a topological Chern insulator phase. While the many-body wave function is constrained to remain topologically trivial under local unitary evolution, we find that the Hall response of the system can dynamically approach a thermal value of the postquench Hamiltonian, even though...

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

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

First-principles studies of spin-orbital physics in pyrochlore oxides

Shinaoka, Hiroshi ; Motome, Yukitoshi ; Miyake, Takashi ; Ishibashi, Shoji ; Werner, Philipp

In: Journal of Physics: Condensed Matter, 2019, vol. 31, no. 32, p. 323001

The pyrochlore oxides A2B2O7 exhibit a complex interplay between geometrical frustration, electronic correlations, and spin–orbit coupling (SOC), due to the lattice structure and active charge, spin, and orbital degrees of freedom. Understanding the properties of these materials is a theoretical challenge, because their intricate nature depends on material-specific details and quantum...

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...