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arXiv:2110.08574 · Physical Review Research

Nonequilibrium dynamics in pumped Mott insulators

Satoshi Ejima, Florian Lange, Holger Fehske

Published Feb 9, 2022• 22 citations
arXivHTMLPDF

Abstract

We use time-evolution techniques for (infinite) matrix product states to calculate, directly in the thermodynamic limit, the time-dependent photoemission spectra and dynamic structure factors of the half-filled Hubbard chain after pulse irradiation.These quantities exhibit clear signatures of the photoinduced phase transition from insulator to metal that occurs because of the formation of so-called η pairs.In addition, the spin dynamic structure factor loses spectral weight in the whole momentum space, reflecting the suppression of antiferromagnetic correlations due to the buildup of η-pairing states.The numerical method demonstrated in this work can be readily applied to other one-dimensional models driven out of equilibrium by optical pumping.

DOI
10.1103/physrevresearch.4.l012012

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We use time-evolution techniques for (infinite) matrix product states to calculate, directly in the thermodynamic limit, the time-dependent photoemission spectra and dynamic structure factors of the half-filled Hubbard chain after pulse irradiation.These quantities exhibit clear signatures of the photoinduced phase transition from insulator to metal that occurs because of the formation of so-called η pairs.In addition, the spin dynamic structure factor loses spectral weight in the whole momentum space, reflecting the suppression of antiferromagnetic correlations due to the buildup of η-pairing states.The numerical method demonstrated in this work can be readily applied to other one-dimensional models driven out of equilibrium by optical pumping.
Utilizing time-evolution techniques in (infinite) matrix-product-state representation, we study the non-equilibrium dynamics of driven Mott insulators and demonstrate photoinduced \eta η pairing directly in the thermodynamic limit. Analyzing the time evolution of the corresponding pairing correlations, we determine the optimal laser pump parameters for which long-range \eta η -pairing becomes dominant after pulse irradiation. The time-dependent photoemission spectra for this optimal pump parameter set show clear signatures of the photoinduced insulator-to-metal phase transition related to the formation of \eta η pairs.
Entanglement analysis of photoinduced η\etaη-pairing states
Abstract Simulating the von Neumann and second-order Rényi entropies of driven Mott insulators, we examine the entanglement dynamics of the η\etaη η -pairing state in the one-dimensional half-filled Hubbard model after pulse irradiation. Corresponding data are obtained by means of the infinite time-evolving block decimation technique directly in the thermodynamic limit. For optimal pump-pulse parameters the temporal course of the entanglement entropies shows the characteristic entanglement growth due to the increase of η\etaη η -pairing correlations.
Using matrix product state techniques we study the nonequilibrium dynamical response of the half-filled Hubbard ladder when subject to an optical pump. Optical pumping offers a way of producing and manipulating new strongly correlated phenomena by suppressing existing magnetic correlations. The ladder allows the effects of pump directionality to be investigated, and compared to a single chain it has strong spin-charge coupling and a fully gapped excitation spectrum, promising different nonequilibrium physics. We compute time-dependent correlations, including the nonequilibrium dynamical structure factors for spin and charge. By deriving a combined spin-charge sum rule that applies both in and out-of-equilibrium, we show that spectral weight is pumped directly from the antiferromagnetic spin response into a low energy ω ∼ 0 charge response below the Mott gap. The transfer of weight is pump direction dependent: pumping directed along the legs disrupts magnetic correlations more than pumping in the rung-direction, even if the post-pump energy density is similar. The charge correlation length is dramatically enhanced by the pump, whilst the spin correlations are most strongly suppressed at nearest- and next-nearest-neighbor spacings. After the pump the system is in a nonthermal correlated metallic state, with gapless charge excitations and approximately equal spin and charge correlation lengths, emphasizing the importance of treating these degrees of freedom on an equal footing in nonequilibrium systems.
Utilizing the time-dependent density-matrix renormalization-group technique, we numerically prove photoinduced pairing states in the extended Falicov-Kimball model (EFKM) at half-filling, both with and without internal SU(2) symmetry. In the time-dependent photoemission spectra, an extra band appears above the Fermi energy after pulse irradiation, indicating an insulator-to-metal transition. Even in the absence of the SU(2) structure, the pair correlations are enhanced during the pump, and afterwards they decrease over time. This implies the possible metallization of Ta2NiSe5{\mathrm{Ta}}_{2}\mathrm{Ni}{\mathrm{Se}}_{5}Ta2​NiSe5​, a strong candidate for an excitonic insulator material, for which the EFKM is considered to be the minimal theoretical model. Simulating the photoemission with optimized pulse parameters, we demonstrate a photoinduced quantum phase transition, in accord with recent findings in time- and angle-resolved photoemission spectroscopy experiments on Ta2NiSe5{\mathrm{Ta}}_{2}\mathrm{Ni}{\mathrm{Se}}_{5}Ta2​NiSe5​.
Based on the nonperturbative many-body time-dependent approach, photoinduced Hubbard band mixing by ultrashort laser pulse is found in a one-dimensional half-filled Hubbard model through the optical conductivity. The nonlinear development of Drude-like (metallic) weight in the resonant optical pumping (${\ensuremath{\omega}}_{\mathrm{pu}}\ensuremath{\approx}{E}_{g}$; ${\ensuremath{\omega}}_{\mathrm{pu}}$ is the pumping laser energy and Eg{E}_{g}Eg​ is the gap energy) indicates reconstruction and mixing of the upper and lower Hubbard bands, in contrast to the case of linear development in off-resonant pumping $({\ensuremath{\omega}}_{\mathrm{pu}}⪢{E}_{g})$ where the rigid band picture is valid. The photoemission response after the ultrashort pulse confirms our finding.