Motivated by the recent development of time-resolved resonant-inelastic x-ray scattering (TRRIXS) in photoexcited antiferromagnetic Mott insulators, we numerically investigate momentum-dependent transient spin dynamics in a half-filled Hubbard model on a square lattice. After turning off a pumping photon pulse, the intensity of a dynamical spin structure factor temporally oscillates with frequencies determined by the energy of two magnons in the antiferromagnetic Mott insulator. We find an antiphase behavior in the oscillations between two orthogonal momentum directions, parallel and perpendicular to the electric field of a pump pulse. The phase difference comes from the $B_{1g}$ channel of the two-magnon excitation. Observing the antiphase oscillations will be a big challenge for TRRIXS experiments when their time resolution will be improved by more than an order of magnitude.
The photoexcitation of a Mott insulator on a square lattice weakens the intensity of both single- and two-magnon excitations as observed in time-resolved resonant-inelastic X-ray scattering and time-resolved Raman scattering, respectively. However, the spectral changes in the low-energy regions below the magnons have not yet been clearly understood. To uncover the nature of the photoinduced low-energy magnetic excitations of the Mott insulator, we numerically investigate the transient magnetic dynamics in a photoexcited half-filled Hubbard model on a square lattice. After turning off a pump pu…
The dissociation of excitons into holes and electrons in photoexcited semiconductors, despite being one of the first recognized examples of a Mott transition, still defies a complete understanding, especially regarding the character of the transition, which is first order in some cases and second order in others. Here we consider an idealized model of photoexcited semiconductors that can be mapped onto a spin-polarised half-filled Hubbard model, whose phase diagram reproduces most of the phenomenology of photoexcited semiconductors and uncovers the key role of the exciton binding energy in det…
Competition between ordered phases, and their associated phase transitions, are significant in the study of strongly correlated systems. Here we examine one aspect, the nonequilibrium dynamics of a photoexcited Mott-Peierls system, using an effective Peierls-Hubbard model and exact diagonalization. Near a transition where spin and charge become strongly intertwined, we observe anti-phase dynamics and a coupling-strength-dependent suppression or enhancement in the static structure factors. The renormalized bosonic excitations coupled to a particular photoexcited electron can be extracted, which…
Mott insulators sometimes show dramatic changes in their electronic states after photoirradiation, as indicated by photoinduced Mott-insulator-to-metal transition. In the photoexcited states of Mott insulators, electron wavefunctions are more delocalized than in the ground state, and long-range Coulomb interactions play important roles in charge dynamics. However, their effects are difficult to discriminate experimentally. Here, we show that in a one-dimensional Mott insulator, bis(ethylenedithio)tetrathiafulvalene-difluorotetracyanoquinodimethane (ET-F2TCNQ), long-range Coulomb interactions s…
Many-body Effects on Excitonic Optical Properties of Photoexcited Semiconductor Quantum Wire Structures
通过求解动态屏蔽的Bethe-Salpeter方程，研究了载流子相互作用引起的多体效应对高度光激发的一维半导体量子线系统激子光学性质的影响.包括电子/空穴自能和电子-空穴相互作用顶点函数中的动态屏蔽效应，我们发现对于大范围的光激发密度（$n= 0-6\times 10^5$ cm $^{-1}$），激子吸收基本上在恒定能量处达到峰值，高于该峰值吸收峰消失而没有明显的增益，即，观察到\textit{no}激子到自由电子-空穴等离子体的Mott跃迁，与以前的理论结果相反，但与最近的实验结果一致。这种增益的缺乏（或莫特跃迁的不存在）源于一维等离子体激元或电荷密度激发的强非弹性散射，与一维系统的非费米液体性质密切相关。我们的理论工作证明了一维光激发电子-空穴系统从低密度区（$n<10^5$ cm $^{-1}$）的非相互作用激子稀气体的有效费米液体行为到高密度区（$n>10^5$ cm $^{-1}$）的非费米液体行为的转变或交叉.对该问题进行了常规的准静态近似，并与全动力学结果进行了比较。激子结合能和吸收光谱的数值结果作为载流子密度和温度的函数。
We study the non-equilibrium response of a 4x3 Hubbard model at U=8 under the influence of a short electric field pulse, with the main focus on multiple photon excitations and on the change of double occupancy after the pulse. The behavior mainly depends on the driving frequency of the electric field. The largest change of double occupancy occurs during the pulse. For frequencies below the Mott gap, we observe multiphoton excitations at large field intensities. For frequencies beyond the gap energy, there is a region where Auger recombination reduces the double occupancy after the pulse. Impac…
We present a theory for the recombination of (charged) holons and doublons in one-dimensional organic Mott insulators, which is responsible for the decay of a photoexcited metallic state. Due to the charge-spin separation, the dominant mechanism for recombination at low density of charges involves a multi-phonon emission. We show that a reasonable coupling to phonons is sufficient to explain the fast recombination observed by pump-probe experiments in ET-F$_2$TCNQ, whereby we can also account for the measured pressure dependence of the recombination rate.
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…
Motivated by the recent progress in time-resolved nonequilibrium spectroscopy in condensed matter, we study an optically excited one-dimensional ionic Hubbard model by exact diagonalization. The model is relevant to organic crystals, transition metal oxides, or ultracold atoms in optical lattices. We implement numerical pump-probe measurements to calculate time-dependent conductivity and single-particle spectral functions. In general, short optical excitation induces a metallic behavior imprinted as a Drude peak in conductivity or an in-gap density of states. In a Mott insulator, we find that …
We study the nonequilibrium dynamics of photoexcited electrons in the narrow-gap Mott insulator VO$_2$. The initial stages of relaxation are treated using a quantum Boltzmann equation methodology, which reveals a rapid ($\sim$ femtosecond time scale) relaxation to a pseudothermal state characterized by a few parameters that vary slowly in time. The long-time limit is then studied by a Hartree-Fock methodology, which reveals the possibility of nonequilibrium excitation to a new metastable $M_1$ metal phase that is qualitatively consistent with a recent experiment. The general physical picture o…
Manipulating spin fluctuations with ultrafast laser pulses is a promising route to dynamically control collective phenomena in strongly correlated materials. However, understanding how photoexcited spin degrees of freedom evolve at a microscopic level requires a momentum- and energy-resolved characterization of their nonequilibrium dynamics. Here, we study the photoinduced dynamics of finite-momentum spin excitations in two-dimensional Mott insulators on a square lattice. By calculating the time-resolved resonant inelastic x-ray scattering cross-section, we show that an ultrafast pump above th…
The recently discovered cuprate superconductor Ba$_2$CuO$_{3+δ}$ exhibits a high $T_c\simeq73$K at $δ\simeq0.2$. The polycrystal grown under high pressure has a structure similar to La$_2$CuO$_4$, but with dramatically different lattice parameters due to the CuO$_6$ octahedron compression. The crystal field in the compressed Ba$_2$CuO$_4$ leads to an inverted Cu $3d$ $e_g$ complex with the $d_{x^2-y^2}$ orbital sitting below the $d_{3z^2-r^2}$ and an electronic structure highly unusual compared to the conventional cuprates. We construct a two-orbital Hubbard model for the Cu $d^9$ state at hol…
Spectral signatures of spin textures and the emergence of a pseudogap
École Polytechnique Fédérale de Lausanne（洛桑联邦理工学院）；California Institute of Technology（加州理工学院）；SISSA, Scuola Internazionale Superiore di Studi Avanzati（国际高等研究院）；CNR-IOM, Istituto Officina dei Materiali（材料研究所）
