# ERC project UfastU

### Theory of ultra-fast dynamics in correlated multi-band systems

ERC Starting Grant 716648 (UfastU)

###### Project summary:

Pump-probe experiments with femtosecond laser pulses allow to study solids on the intrinsic timescale of their microscopic constituents, and have opened an entirely new direction in the field of condensed matter physics. Of particular interest in this context are strongly correlated materials, in which the collective behavior of many particles gives rise to emergent phenomena such as magnetism, high-temperature superconductivity, or interaction- induced metal-insulator transitions. Seminal experiments, including the finding of light-induced superconductivity and photo-induced transitions to hidden phases in materials with highly entangled orbital, spin, and lattice degrees of freedom show that the rich equilibrium phase diagrams in correlated systems are most certainly complemented by an equally rich but unexplored manifold of non-equilibrium states. An access to this terrain would not only answer fundamental questions of many-body physics, but it may also bring about new concepts for technological applications such as femtosecond switches and optically controlled magnetic memory, or lead to a better understanding of transport processes in photovoltaic devices.

The remarkable experimental progress is contrasted by a rather limited theoretical understanding of non-equilibrium processes in correlated systems. Most microscopic theory has been based on single-band models with ad-hoc parameters, while many of the emergent phenomena in correlated materials are intimately connected to the presence of more than one active degree of freedom. Our central objective is thus to develop a versatile computational tool which can describe correlated multi- band systems with dynamic interactions and help to identify new ways to manipulate their cooperative behavior far from equilibrium. With this, we would like to lay the foundations for an ab-initio approach to the real-time dynamics of correlated materials based on the dynamical mean-field theory (DMFT) and its extensions. This methodological advance would, e.g., open the possibility to understand light-induced superconductivity in multi-orbital materials such as iron pnictides or doped fullerenes.

###### Project publications:

**Preprints**

- Philipp Werner, Steven Johnston, Martin Eckstein,
*Nonequilibrium-DMFT based RIXS investigation of the two-orbital Hubbard model*, arXiv:2012.10067. - Martin Eckstein, Philipp Werner,
*Simulation of time-dependent resonant inelastic X-ray scattering using non-equilibrium dynamical mean-field theory*, arXiv:2012.09921. - Jiajun Li, Nagamalleswararao Dasari, Martin Eckstein,
*Ultrafast dynamics in relativistic Mott insulators*,arXiv:2010.09253. - Nagamalleswararao Dasari, Jiajun Li, Philipp Werner, Martin Eckstein,
*A photo-induced strange metal with electron and hole quasi-particles*, arXiv:2010.04095. - Antonio Picano and Martin Eckstein,
*Accelerated gap collapse in a Slater antiferromagnet*, arXiv:2009.04961. - Francesco Grandi, Jiajun Li, Martin Eckstein,
*Ultrafast Mott transition driven by nonlinear phonons*, arXiv:2005.14100. - Nikolaj Bittner, Denis Golež, Martin Eckstein, Philipp Werner, Effects of frustration on the nonequilibrium dynamics of photo-excited lattice systems, arXiv:2005.11722
- Jiajun Li, Denis Golez, Philipp Werner, Martin Eckstein,
*Superconducting optical response of photodoped Mott insulators*, arXiv:2001.00184 (2020). arXiv:2001.00184

**2020**

- Katharina Lenk and Martin Eckstein,
*Collective excitations of the U(1)-symmetric exciton insulator in a cavity,*Phys. Rev. B**102**, 205129 (2020). - Jiajun Li, Martin Eckstein,
*Manipulating intertwined orders in solids with quantum light*,Phys. Rev. Lett.**125**, 217402 (2020). - V. N. Valmispild, C. Dutreix, M. Eckstein, M. I. Katsnelson, A. I. Lichtenstein, E. A. Stepanov,
*Dynamically induced doublon repulsion in the Fermi-Hubbard model probed by a single-particle density of states*, Phys. Rev. B**102**, 220301(R) (2020). - Jiajun Li, Denis Golez, Philipp Werner, Martin Eckstein,
*η-paired superconducting hidden phase in photodoped Mott insulators*, Phys. Rev. B**102**, 165136 (2020). - Riku Tuovinen, Denis Golež, Martin Eckstein, Michael A. Sentef,
*Comparing the generalized Kadanoff-Baym ansatz with the full Kadanoff-Baym equations for an excitonic insulator out of equilibrium,*Phys. Rev. B**102**, 115157 (2020). - Michael Schüler, Denis Golež, Yuta Murakami, Nikolaj Bittner, Andreas Hermann, Hugo U. R. Strand, Philipp Werner, Martin Eckstein,
*NESSi: The Non-Equilibrium Systems Simulation package*, Comp. Phys. Comm. (2020) doi.org/10.1016/j.cpc.2020.107484. arXiv:1911.01211 - Michael A. Sentef, Jiajun Li, Fabian Künzel, Martin Eckstein,
*Quantum to classical crossover of Floquet engineering in correlated quantum systems*, Phys. Rev. Research**2**, 033033 (2020).

- Jiajun Li, Denis Golez, Giacomo Mazza, Andrew Millis, Antoine Georges, Martin Eckstein,
*Electromagnetic coupling in tight-binding models for strongly correlated light and matter,*Phys. Rev. B**101**, 205140 (2020). - Nagamalleswararao Dasari, Jiajun Li, Philipp Werner, Martin Eckstein,
*Revealing Hund’s multiplets in Mott insulators under strong electric fields*, arXiv:1907.00754 (2019). Phys. Rev. B**101**, 161107(R) (2020) - Nikolaj Bittner, Denis Golez, Martin Eckstein, Philipp Werner,
*Photo-enhanced excitonic correlations in a Mott insulator with nonlocal interactions*, Phys. Rev. B**101**, 085127 (2020).

**2019**

- P. Werner, M. Eckstein, M. Müller, G. Refael,
*Cooling by photo-doping – Light-induced symmetry breaking in the Hubbard model*, Nature Comm. 1**0**, 5556 (2019) - D. Golez, M. Eckstein, P. Werner,
*Multi-band non-equilibrium GW+EDMFT formalism for correlated insulators*, Phys. Rev. B**100**, 235117 (2019) - N. Dasari, M. Eckstein,
*Ultra-fast electric field controlled spin-fluctuations in the Hubbard model*, Phys. Rev. B**100**, 121114(R) (2019) - C. Stahl, M. Eckstein,
*Noise Correlations in time- and angular-resolved photoemission spectroscopy*, Phys. Rev. B**99**, 241111(R) (2019) - D. Golez, L. Boehnke, M. Eckstein, P. Werner,
*Dynamics of photo-doped charge transfer insulators*, Phys. Rev. B**100**, 041111(R) (2019) - Philipp Werner, Jianju Li, Denis Golez, Martin Eckstein,
*Entropy-cooled nonequilibrium states of the Hubbard model*, Phys. Rev. B**100**, 155130 (2019)

**2018**

- R. Tuovinen, D. Golez, M. Schüler, P. Werner, M. Eckstein, M. A. Sentef,
*Adiabatic Preparation of a Correlated Symmetry-Broken Initial State with the Generalized Kadanoff–Baym Ansatz*, arXiv:1808.00712 (2018). Physics Status Solid B,**257**(2018) - N. Dasari, M. Eckstein,
*Transient Floquet engineering of superconductivity*, Phys. Rev. B**98**, 235149 (2018).http://dx.doi.org/10.1103/PhysRevB.98.235149 - A. Matthies, J. Li, M. Eckstein,
*Control of*competing*superconductivity and charge order by nonequilibrium currents*, Phys. Rev. B**98**, 180502 (2018).http://dx.doi.org/10.1103/PhysRevB.98.180502 - J. Li, H. U. R. Strand, P. Werner, M. Eckstein,
*Theory of photoinduced ultrafast switching to a spin-orbital ordered hidden phase*, Nature Communications**9**, 4581 (2018).http://dx.doi.org/10.1038/s41467-018-07051- - M. Wais, M. Eckstein, R. Fischer, P. Werner, M. Battiato, K. Held,
*Quantum Boltzmann equation for strongly correlated systems: Comparison to dynamical mean field theory*, Phys. Rev. B**98**, 134312 (2018).http://dx.doi.org/10.1103/PhysRevB.98.134312 - N. Dasari, M. Eckstein,
*Photoexcited states in correlated band insulators*, Phys. Rev. B**98**, 035113 (2018). http://dx.doi.org/10.1103/PhysRevB.98.035113 - N. Bittner, D. Golez, H. U. R. Strand, M. Eckstein, P. Werner,
*Coupled charge and spin dynamics in a photoexcited doped Mott insulator*, Phys. Rev. B**97**, 235125 (2018). http://dx.doi.org/10.1103/PhysRevB.97.235125 - P. Werner, H. U. R. Strand, S. Hoshino, Y. Murakami, M. Eckstein,
*Enhanced pairing susceptibility in a photodoped two-orbital Hubbard model*, Phys. Rev. B**97**, 165119 (2018). http://dx.doi.org/10.1103/PhysRevB.97.165119