Université de Fribourg

Ultrafast dynamics of the surface photovoltage in potassium-doped black phosphorus

Kremer, Geoffroy ; Rumo, Maxime ; Yue, Changming ; Pulkkinen, Aki ; Nicholson, Christopher W. ; Jaouen, Thomas ; Von Rohr, Fabian ; Werner, Philipp ; Monney, Claude

In: Physical Review B, 2021, vol. 104, no. 3, p. 035125

Black phosphorus is a quasi-two-dimensional layered semiconductor with a narrow direct band gap of 0.3 eV. A giant surface Stark effect can be produced by the potassium doping of black phosphorus, leading to a semiconductor to semimetal phase transition originating from the creation of a strong surface dipole and associated band bending. By using time- and angle-resolved photoemission ...

Université de Fribourg

Nonthermal excitonic condensation near a spin-state transition

Werner, Philipp ; Murakami, Yuta

In: Physical Review B, 2020, vol. 102, no. 2020-24, p. 241103

Recent experiments demonstrate the induction of long-range order in correlated electron systems via external perturbations, which calls for a better understanding of nonthermal ordered states and nonequilibrium symmetry breaking. Here, we reveal a mechanism based on entropy cooling and entropy trapping in a strongly correlated multiorbital system. We consider a two-orbital Hubbard model with...

Université de Fribourg

${\eta}$-paired superconducting hidden phase in photodoped Mott insulators

Li, Jiajun ; Golez, Denis ; Werner, Philipp ; Eckstein, Martin

In: Physical Review B, 2020, vol. 102, no. 16, p. 165136

We show that a metastable η-pairing superconducting phase can be induced by photodoping doublons and holes into a strongly repulsive fermionic Hubbard model. The doublon-hole condensate originates from an intrinsic doublon-hole exchange interaction and does not rely on the symmetry of the half-filled Hubbard model. It extends over a wide range of doublon densities and effective temperatures....

Université de Fribourg

NESSi : The Non-Equilibrium Systems Simulation package

Schüler, Michael ; Golež, Denis ; Murakami, Yuta ; Bittner, Nikolaj ; Herrmann, Andreas ; U.R.Strand, Hugo ; Werner, Philipp ; Eckstein, Martin

In: Computer Physics Communications, 2020, vol. 257, no. 2020, p. 107484

The nonequilibrium dynamics of correlated many-particle systems is of interest in connection with pump–probe experiments on molecular systems and solids, as well as theoretical investigations of transport properties and relaxation processes. Nonequilibrium Green’s functions are a powerful tool to study interaction effects in quantum many-particle systems out of equilibrium, and to extract...

Université de Fribourg

Entropy and electronic orders of the three-orbital Hubbard model with antiferromagnetic Hund coupling

Yue, Changming ; Hoshino, Shintaro ; Werner, Philipp

In: Physical Review B, 2020, vol. 102, no. 19, p. 195103

An antiferromagnetic Hund coupling in multiorbital Hubbard systems induces orbital freezing and an associated superconducting instability, as well as unique composite orders in the case of an odd number of orbitals. While the rich phase diagram of the half-filled three-orbital model has recently been explored in detail, the properties of the doped system remain to be clarified. Here, we...

Université de Fribourg

How circular dichroism in time- and angle-resolved photoemission can be used to spectroscopically detect transient topological states in graphene

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

In: Physical Review X, 2020, vol. 10, no. 4, p. 041013

Pumping graphene with circularly polarized light is the archetype of light-tailoring topological bands. Realizing the induced Floquet-Chern-insulator state and demonstrating clear experimental evidence for its topological nature has been a challenge, and it has become clear that scattering effects play a crucial role. We tackle this gap between theory and experiment by employing microscopic...

Université de Fribourg

Ultrafast coupled charge and spin dynamics in strongly correlated NiO

Gillmeister, Konrad ; Golež, Denis ; Chiang, Cheng-Tien ; Bittner, Nikolaj ; Pavlyukh, Yaroslav ; Berakdar, Jamal ; Werner, Philipp ; Widdra, Wolf

In: Nature Communications, 2020, vol. 11, no. 1, p. 4095

Charge excitations across an electronic band gap play an important role in opto- electronics and light harvesting. In contrast to conventional semiconductors, studies of above-band-gap photoexcitations in strongly correlated materials are still in their infancy. Here we reveal the ultrafast dynamics controlled by Hund’s physics in strongly correlated photoexcited NiO. By combining...

Université de Fribourg

High-harmonic generation in spin-orbit coupled systems

Lysne, Markus ; Murakami, Yuta ; Schüler, Michael ; Werner, Philipp

In: Physical Review B, 2020, vol. 102, no. 8, p. 081121

We study high-harmonic generation in two-dimensional electron systems with Rashba and Dresselhaus spin-orbit coupling and derive harmonic generation selection rules with the help of group theory. Based on the band structures of these minimal models and explicit simulations we reveal how the spin-orbit parameters control the cutoff energy in the high-harmonic spectrum. We also show that the...

Université de Fribourg

Superconducting optical response of photodoped Mott insulators

Li, J. ; Golez, D. ; Werner, Philipp ; Eckstein, M.

In: Modern Physics Letters B, 2020, vol. 34, no. 19n20, p. 2040054

Ultrafast laser pulses can redistribute charges in Mott insulators on extremely short time scales, leading to the fast generation of photocarriers. It has recently been demonstrated that these photocarriers can form a novel η-paired condensate at low temperatures, featuring a staggered superconducting pairing field. In this conference paper, we discuss the origin of the η-paired hidden...

Université de Fribourg

Entropy and specific heat of the infinite-dimensional three-orbital Hubbard model

Yue, Changming ; Werner, Philipp

In: Physical Review B, 2020, vol. 102, no. 8, p. 085102

The Hund's coupling in multiorbital Hubbard systems induces spin freezing and associated Hund metal behavior. Using dynamical mean-field theory, we explore the effect of local moment formation, spin, and charge excitations on the entropy and specific heat of the three-orbital model. For fillings 2≲n<3 and low temperature, we demonstrate a substantial enhancement of the entropy in the...