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arXiv:2401.12584 · APL Materials

Keldysh crossover in one-dimensional Mott insulators

Kazuya Shinjo, Takami Tohyama

Published Apr 1, 2024• 5 citations
arXivHTMLPDF

Abstract

Recent advancements in pulse laser technology have facilitated the exploration of nonequilibrium spectroscopy of electronic states in the presence of strong electric fields across a broad range of photon energies. The Keldysh crossover serves as an indicator that distinguishes between excitations resulting from photon absorption triggered by near-infrared multicycle pulses and those arising from quantum tunneling induced by terahertz pulses. Using a time-dependent density-matrix renormalization group, we investigate the emergence of the Keldysh crossover in a one-dimensional (1D) Mott insulator. We find that the Drude weight is proportional to photo-doped doublon density when a pump pulse induces photon absorption. In contrast, the Drude weight is suppressed when a terahertz pulse introduces doublons and holons via quantum tunneling. The suppressed Drude weight accompanies glassy dynamics with suppressed diffusion, which is a consequence of strong correlations and exhibits finite polarization decaying slowly after pulse irradiation. In the quantum tunneling region, entanglement entropy slowly grows logarithmically. These contrasting behaviors between the photon-absorption and quantum tunneling regions are a manifestation of the Keldysh crossover in 1D Mott insulators and provide a novel methodology for designing the localization and symmetry of electronic states called subcycle-pulse engineering.

DOI
10.1063/5.0198384

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Recent advancements in pulse laser technology have facilitated the exploration of nonequilibrium spectroscopy of electronic states in the presence of strong electric fields across a broad range of photon energies. The Keldysh crossover serves as an indicator that distinguishes between excitations resulting from photon absorption triggered by near-infrared multicycle pulses and those arising from quantum tunneling induced by terahertz pulses. Using a time-dependent density-matrix renormalization group, we investigate the emergence of the Keldysh crossover in a one-dimensional (1D) Mott insulator. We find that the Drude weight is proportional to photo-doped doublon density when a pump pulse induces photon absorption. In contrast, the Drude weight is suppressed when a terahertz pulse introduces doublons and holons via quantum tunneling. The suppressed Drude weight accompanies glassy dynamics with suppressed diffusion, which is a consequence of strong correlations and exhibits finite polarization decaying slowly after pulse irradiation. In the quantum tunneling region, entanglement entropy slowly grows logarithmically. These contrasting behaviors between the photon-absorption and quantum tunneling regions are a manifestation of the Keldysh crossover in 1D Mott insulators and provide a novel methodology for designing the localization and symmetry of electronic states called subcycle-pulse engineering.
The elucidation of nonequilibrium states in strongly correlated systems holds the key to emergence of novel quantum phases.The nonequilibrium-induced insulator-to-metal transition is particularly interesting since it reflects the fundamental nature of competition between itinerancy and localization of the charge degrees of freedom.We investigate pulse-excited insulator-to-metal transition of the half-filled one-dimensional extended Hubbard model.Calculating the time-dependent optical conductivity with the time-dependent density-matrix renormalization group, we find that strong mono-and half-cycle pulses inducing quantum tunneling strongly suppress spectral weights contributing to the Drude weight σ D , even if we introduce a large number of carriers n d .This is in contrast to a metallic behavior of σ D ∝ n d induced by photon absorption and chemical doping.The strong suppression of σ D in quantum tunneling is a result of the emergence of the Hilbert-space fragmentation, which makes pulse-excited states glassy.
Doublon-hole pair production which takes place during dielectric breakdown in a Mott insulator subject to a strong laser or a static electric field is studied in the one-dimensional Hubbard model. Two nonlinear effects cause the excitation, i.e., multi-photon absorption and quantum tunneling. Keldysh crossover between the two mechanisms occurs as the field strength and photon energy is changed. The calculation is done analytically by the Landau-Dykhne method in combination with the Bethe ansatz solution and the results are compared with those of the time dependent density matrix renormalization group. Using this method, we calculate distribution function of the generated doublon-hole pairs and show that it drastically changes as we cross the Keldysh crossover line. After calculating the tunneling threshold for several representative one-dimensional Mott insulators, possible experimental tests of the theory is proposed such as angle resolved photoemission spectroscopy of the upper Hubbard band in the quantum tunneling regime. We also discuss the relation of the present theory with a many-body extension of electron-positron pair production in nonlinear quantum electrodynamics known as the Schwinger mechanism.
Doublon-hole pair production which takes place during dielectric breakdown in a Mott insulator subject to a strong laser or a static electric field is studied in the one-dimensional Hubbard model. Two nonlinear effects cause the excitation, i.e., multi-photon absorption and quantum tunneling. Keldysh crossover between the two mechanisms occurs as the field strength and photon energy is changed. The calculation is done analytically by the Landau-Dykhne method in combination with the Bethe ansatz solution and the results are compared with those of the time dependent density matrix renormalization group. Using this method, we calculate distribution function of the generated doublon-hole pairs and show that it drastically changes as we cross the Keldysh crossover line. After calculating the tunneling threshold for several representative one-dimensional Mott insulators, possible experimental tests of the theory is proposed such as angle resolved photoemission spectroscopy of the upper Hubbard band in the quantum tunneling regime. We also discuss the relation of the present theory with a many-body extension of electron-positron pair production in nonlinear quantum electrodynamics known as the Schwinger mechanism.
Doublon-hole pair production, which takes place during dielectric breakdown in a Mott insulator subject to a strong laser or a static electric field, is studied in the one-dimensional Hubbard model. Two nonlinear effects cause the excitation, i.e., multiphoton absorption and quantum tunneling. Keldysh crossover between the two mechanisms occurs as the field strength and photon energy are changed. The calculation is done analytically by the Landau-Dykhne method in combination with the Bethe ansatz solution, and the results are compared with those of the time-dependent density matrix renormalization group. Using this method, we calculate the distribution function of the generated doublon-hole pairs and show that it drastically changes as we cross the Keldysh crossover line. After calculating the tunneling threshold for several representative one-dimensional Mott insulators, possible experimental tests of the theory are proposed, such as angle-resolved photoemission spectroscopy of the upper Hubbard band in the quantum tunneling regime. We also discuss the relationship of the present theory with a many-body extension of electron-positron pair production in nonlinear quantum electrodynamics, known as the Schwinger mechanism.
We investigate changes in the optical conductivity of doped Mott insulators by tuning ultrashort pump pulses to target either the Drude or low-energy absorption regions. Using a hole-doped two-leg Hubbard ladder and a four-leg t-J ladders, we calculate the optical conductivity after pump by employing the time-dependent density matrix renormalization group. We find that a monocycle electric field pulse tuned to the Drude absorption reduces the Drude weight, accompanied by a slight enhancement in the mid-infrared (mid-IR) spectral weight. However, this enhancement diminishes as the pulse intensity increases. In contrast, a pump pulse tuned to the mid-IR absorption only affects the Drude weight. This behavior arises because the mid-IR absorption originates from magnetic excitations that do not couple directly to photons. These predictions can be tested experimentally by applying ultrashort low-energy pump pulses to cuprate materials.
We theoretically investigate the relaxation of photogenerated charge carriers in one-dimensional Mott insulators. We adopt the Pariser–Parr–Pople model, and numerically calculate the time development of the nonequilibrium state excited by a weak light pulse. We investigate the dependence of the dynamics on the Coulomb correlation strength in the case where the binding effect between photogenerated opposite charges is significant. In the strong-correlation region (U≫WU \gg WU≫W), where U is the onsite Coulomb interaction energy and W is the bandwidth, the Auger recombination where two bound holon–doublon pairs decay into one unbound holon–doublon pair dominates the decay dynamics. From the strong- to intermediate (U≃WU \simeq WU≃W)-correlation regions, the Auger recombination is always dominant, but the charge carriers involved in the process cannot be described by a holon and a doublon in the intermediate-correlation region. In the crossover region between these two regions, the Auger coefficient is strongly enhanced, and the decay time constant is consistent with those obtained in recent experiments.