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arXiv:2007.04636 · Physical Review Research

Photoinduced η -pairing at finite temperatures

Satoshi Ejima, Tatsuya Kaneko, Florian Lange, Seiji Yunoki, Holger Fehske

Published Jul 8, 2020• 30 citations
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Abstract

The paper presents photoinduced $\ensuremath{\eta}$-pairing in a half-filled infinite Hubbard chain at finite temperatures by means of unbiased numerical techniques. The authors excite the Mott insulating phase by a light pulse and monitor the time-evolution of the many-body system after irradiation, and show the enhancement of $\ensuremath{\eta}$-pairing correlations and how to control it.

DOI
10.1103/physrevresearch.2.032008

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The paper presents photoinduced \ensuremathη\ensuremath{\eta}\ensuremathη-pairing in a half-filled infinite Hubbard chain at finite temperatures by means of unbiased numerical techniques. The authors excite the Mott insulating phase by a light pulse and monitor the time-evolution of the many-body system after irradiation, and show the enhancement of \ensuremathη\ensuremath{\eta}\ensuremathη-pairing correlations and how to control it.
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.
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.
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.
Employing the density-matrix renormalization group technique in the matrix-product-state representation, we investigate the photoexcited superconducting correlations induced by the η-pairing mechanism in the half-filled Hubbard chain.We estimate the characteristic pair correlation function and verify the accuracy of our numerical results by comparison with exact-diagonalization data for small systems.The optimal parameter set of the pump that most enhances the η-pair correlations, is calculated in the strong-coupling regime.For such a pump, we explore the possibility of quasi-long-range order.
By employing unbiased numerical methods, we show that pulse irradiation can induce unconventional superconductivity even in the Mott insulator of the Hubbard model. The superconductivity found here in the photoexcited state is due to the η-pairing mechanism, characterized by staggered pair-density-wave oscillations in the off-diagonal long-range correlation, and is absent in the ground-state phase diagram; i.e., it is induced neither by a change of the effective interaction of the Hubbard model nor by simple photocarrier doping. Because of the selection rule, we show that the nonlinear optical response is essential to increase the number of η pairs and thus enhance the superconducting correlation in the photoexcited state. Our finding demonstrates that nonequilibrium many-body dynamics is an alternative pathway to access a new exotic quantum state that is absent in the ground-state phase diagram, and also provides an alternative mechanism for enhancing superconductivity.
Photoinduced carrier dynamics in a correlated electron system on a coupled two-leg ladder lattice are studied. The two-leg ladder Hubbard model is analyzed utilizing the exact diagonalization method based on the Lanczos algorithm in finite-size clusters. In order to reveal the transient carrier dynamics after photoirradiation, we calculate the low-energy components of the hole kinetic energy, the pair-field correlation function, the optical conductivity spectra, and other characteristics. It is shown that the photoinduced metallic-like state appears in a half-filled Mott insulating state, while the low-energy carrier motion is suppressed by photoirradiation in the case of hole-doped metallic states. These photoinduced changes in the electron dynamics are associated with changes in the carrier-pair coherence; they are not attributed to a naive thermalization, and are associated with a ladder-lattice effect instead. Based on the numerical results, optical control of hole pairs using double-pulse pumping is demonstrated. Implications for recent optical pump-probe experiments are presented.