Université de Fribourg

Signatures of bosonic excitations in high-harmonic spectra of Mott insulators

Lysne, Markus ; Murakami, Yuta ; Werner, Philipp

In: Physical Review B, 2020, vol. 101, no. 19, p. 195139

The high-harmonic spectrum of the Mott insulating Hubbard model has recently been shown to exhibit plateau structures with cutoff energies determined by nth-nearest- neighbor doublon-holon recombination processes. The spectrum thus allows one to extract the on-site repulsion U. Here, we consider generalizations of the single-band Hubbard model and discuss the signatures of bosonic excitations...

Université de Fribourg

Collective modes in excitonic insulators: Effects of electron-phonon coupling and signatures in the optical response

Murakami, Yuta ; Golež, Denis ; Kaneko, Tatsuya ; Koga, Akihisa ; Millis, Andrew J. ; Werner, Philipp

In: Physical Review B, 2020, vol. 101, no. 19, p. 195118

We consider a two-band spinless model describing an excitonic insulator (EI) on the two-dimensional square lattice with anisotropic hopping parameters and electron-phonon (el-ph) coupling, inspired by the EI candidate Ta2NiSe5. We systematically study the nature of the collective excitations in the ordered phase which originates from the interband Coulomb interaction and the el-ph coupling. ...

Université de Fribourg

Revealing Hund’s multiplets in Mott insulators under strong electric fields

Dasari, Nagamalleswararao ; Li, Jiajun ; Werner, Philipp ; Eckstein, Martin

In: Physical Review B, 2020, vol. 101, no. 16, p. 161107

We investigate the strong-field dynamics of a paramagnetic two-band Mott insulator using real-time dynamical mean-field theory. We demonstrate that strong electric fields can lead to a transient localization of electrons. This nonequilibrium quantum effect allows us to reveal specific signatures of local correlations in the time-resolved photoemission spectrum. In particular, we demonstrate...

Université de Fribourg

Photoenhanced excitonic correlations in a Mott insulator with nonlocal interactions

Bittner, Nikolaj ; Golež, Denis ; Eckstein, Martin ; Werner, Philipp

In: Physical Review B, 2020, vol. 101, no. 8, p. 085127

We investigate the effect of nonlocal interactions on the photodoped Mott insulating state of the two-dimensional Hubbard model using a nonequilibrium generalization of the dynamical cluster approximation. In particular, we compare the situation where the excitonic states are lying within the continuum of doublon-holon excitations to a setup where the excitons appear within the Mott gap. In...

Université de Fribourg

Local Berry curvature signatures in dichroic angle-resolved photoelectron spectroscopy from two-dimensional materials

Schüler, Michael ; Giovannini, Umberto De ; Hübener, Hannes ; Rubio, Angel ; Sentef, Michael A. ; Werner, Philipp

In: Science Advances, 2020, vol. 6, no. 9, p. eaay2730

Topologically nontrivial two-dimensional materials hold great promise for next- generation optoelectronic applications. However, measuring the Hall or spin-Hall response is often a challenge and practically limited to the ground state. An experimental technique for tracing the topological character in a differential fashion would provide useful insights. In this work, we show that circular...

Université de Fribourg

Ultrafast nonequilibrium evolution of excitonic modes in semiconductors

Murakami, Yuta ; Schüler, Michael ; Takayoshi, Shintaro ; Werner, Philipp

In: Physical Review B, 2020, vol. 101, no. 3, p. 035203

We study the time evolution of excitonic states after photoexcitation in the one- dimensional spinless extended Falicov-Kimball model. Several numerical methods are employed and benchmarked against each other: time-dependent mean-field simulations, the second-Born approximation (2BA) within the Kadanoff-Baym formalism, the generalized Kadanoff-Baym ansatz (GKBA) implemented with the 2BA, and...

Université de Fribourg

Nickelate superconductors: multiorbital nature and spin freezing

Werner, Philipp ; Hoshino, Shintaro

In: Physical Review B, 2020, vol. 101, no. 4, p. 041104

Superconductivity with a remarkably high Tc has recently been found in Sr-doped NdNiO2 thin films. While this system bears strong similarities to the cuprates, some differences, such as a weaker antiferromagnetic exchange coupling and possible high-spin moments on the doped Ni sites have been pointed out. Here, we investigate the effect of Hund coupling and crystal field splitting in a simple...

Université de Fribourg

Alleviating the sign problem in quantum Monte Carlo simulations of spin-orbit-coupled multiorbital Hubbard models

Kim, Aaram J. ; Werner, Philipp ; Valentí, Roser

In: Physical Review B, 2020, vol. 101, no. 4, p. 045108

We present a strategy to alleviate the sign problem in continuous-time quantum Monte Carlo (CTQMC) simulations of the dynamical-mean-field-theory (DMFT) equations for the spin-orbit-coupled multiorbital Hubbard model. We first identify the combinations of rotationally invariant Hund coupling terms present in the relativistic basis which lead to a severe sign problem. Exploiting the fact that...

Université de Fribourg

Multiband nonequilibrium G W + EDMFT formalism for correlated insulators

Golež, Denis ; Eckstein, Martin ; Werner, Philipp

In: Physical Review B, 2019, vol. 100, no. 23, p. 235117

We study the dynamics of charge-transfer insulators after a photoexcitation using the three-band Emery model which is relevant for the description of cuprate superconductors. We provide a detailed derivation of the nonequilibrium extension of the multiband GW + EDMFT formalism and the corresponding downfolding procedure. The Peierls construction of the electron-light coupling is generalized...

Université de Fribourg

Light-induced evaporative cooling of holes in the Hubbard model

Werner, Philipp ; Eckstein, Martin ; Müller, Markus ; Refael, Gil

In: Nature Communications, 2019, vol. 10, no. 1, p. 5556

An elusive goal in the field of driven quantum matter is the induction of long-range order. Here, we propose a mechanism based on light-induced evaporative cooling of holes in a correlated fermionic system. Since the entropy of a filled narrow band grows rapidly with hole doping, the isentropic transfer of holes from a doped Mott insulator to such a band results in a drop of temperature....