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

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

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

Classification and characterization of nonequilibrium Higgs modes in unconventional superconductors

Schwarz, L. ; Fauseweh, B. ; Tsuji, N. ; Cheng, N. ; Bittner, Nikolaj ; Krull, H. ; Berciu, M. ; Uhrig, G.S. ; Schnyder, A.P. ; Kaiser, S. ; Manske, D.

In: Nature Communications, 2020, vol. 11, no. 1, p. 1–9

Recent findings of new Higgs modes in unconventional superconductors require a classification and characterization of the modes allowed by nontrivial gap symmetry. Here we develop a theory for a tailored nonequilibrium quantum quench to excite all possible oscillation symmetries of a superconducting condensate. We show that both a finite momentum transfer and quench symmetry allow for an...

Université de Fribourg

Possible light-induced superconductivity in a strongly correlated electron system

Bittner, Nikolaj ; Tohyama, Takami ; Kaiser, Stefan ; Manske, Dirk

In: Journal of the Physical Society of Japan, 2019, vol. 88, no. 4, p. 044704

Using a nonequilibrium implementation of the Lanczos-based exact diagonalisation technique we study the possibility of the light-induced superconducting phase coherence in a solid state system after an ultrafast optical excitation. In particular, we investigate the buildup of superconducting correlations by calculating an exact time- dependent wave function reflecting the properties of the...