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Journal of Physics Conference Series

Antiphase oscillations in the time-resolved spin structure factor of a photoexcited Mott insulator on a square lattice

Takami Tohyama, Kazuya Shinjo, Kenji Tsutsui

Published Mar 1, 2022• 1 citation
Publisher

Abstract

Abstract We investigate momentum-dependent transient spin dynamics after photoirradiation in a two-dimensional Mott insulator described by a half-filled Hubbard model on a square lattice by using a numerically exact-diagonalization technique. We find a temporal oscillation in the static spin structure factor of a <?CDATA $\sqrt {18} \times \sqrt {18} $?> 18 × 18 periodic lattice. The oscillation exhibits an antiphase behavior between, for example, two orthogonal momentum directions parallel and perpendicular to the electric field of a pump pulse. The origin of the antiphase oscillation is attributed to a photoexcited wave function that has overlap with eigenstates producing the B 1g bimagnon Raman intensity. Observing such antiphase oscillations will be a big challenge for time-resolved resonant elastic x-ray scattering experiments.

DOI
10.1088/1742-6596/2164/1/012049

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Abstract We investigate momentum-dependent transient spin dynamics after photoirradiation in a two-dimensional Mott insulator described by a half-filled Hubbard model on a square lattice by using a numerically exact-diagonalization technique. We find a temporal oscillation in the static spin structure factor of a <?CDATA $\sqrt {18} \times \sqrt {18} $?> 18 × 18 periodic lattice. The oscillation exhibits an antiphase behavior between, for example, two orthogonal momentum directions parallel and perpendicular to the electric field of a pump pulse. The origin of the antiphase oscillation is attributed to a photoexcited wave function that has overlap with eigenstates producing the B 1g bimagnon Raman intensity. Observing such antiphase oscillations will be a big challenge for time-resolved resonant elastic x-ray scattering experiments.
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.
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 B1g 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.
Abstract We numerically investigate spectroscopic properties for a two-dimensional Mott insulator described by a half-filled Hubbard model on the square lattice. Firstly, we examine the spectral shape of the optical conductivity by using time-dependent density-matrix renormalization group implemented by the Legendre polynomial expansion. We find a shape peak resembling to an excitonic peak at absorption edge, whose origin is attributable to antiferromagnetic correlation in the spin background. We next investigate momentum-dependent transient charge and spin dynamics after photoirradiation by using time-dependent Lanczos-type exact diagonalization. We find a temporal oscillation in the intensity of the dynamical spin structure factor, which exhibits an antiphase behavior between, for example, two orthogonal momentum directions parallel and perpendicular to the electric field of a pump pulse. Observing such antiphase oscillations will be a big challenge for time-resolved resonant-inelastic x-ray scattering experiments.
We theoretically investigate momentum-dependent spin dynamics that evolve after pumping within a femtosecond timescale in an antiferromagnetic (AFM) Mott insulator on a square lattice. We carry out the numerically exact diagonalization techniques on 18-site cluster of a half-filled Hubbard model. We demonstrate characteristic temporal oscillations for the spin excitation spectrum: They show an antiphase behavior for two orthogonal directions in the momentum space, which are parallel and perpendicular to the electric field of a pump pulse. Decomposing the time-dependent wave function after a pump pulse with the symmetry representation, the A1 component plays a dominant role in the main peak of the spectrum. The antiphase oscillations of the peaks can be explained by the fact that the B1g Raman active state contributes the oscillation. We expect that trRIXS can detect such oscillations when its resolution is improved for a femtosecond timescale.
Abstract Photoexcitation of a Mott insulator on a square lattice has weakened the intensity of both single- and two-magnon as observed in time-resolved resonant-inelastic x-ray scattering and time-resolved Raman scattering. However, the spectral change in low-energy regions below the magnons has not been clarified so far. To uncover the nature of photoinduced low-energy magnetic excitations of the Mott insulator, we numerically investigate transient magnetic dynamics in a photoexcited half-filled Hubbard model on the square lattice. After turning off a pump pulse tuned for an absorption edge, new magnetic signals clearly emerge well below magnon energy in both single- and two-magnon excitations. We find that the low-energy excitations are predominantly created via excitonic states at the absorption edge. These exciton-assisted magnetic excitations may provide a possible explanation for low-energy spectral weight in a recent time-resolved two-magnon Raman scattering experiment for insulating YBa2Cu3O6.1.
Abstract 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 the Mott gap induces a prompt softening of the spin excitation energy, compatible with a transient renormalization of the exchange interaction. While spin fluctuations in a hole-doped system (paramagnons) are well described by Floquet theory, magnons at half filling are found to deviate from this picture. Furthermore, we show that the paramagnon softening is accompanied by an ultrafast suppression of d-wave pairing correlations, indicating a link between the transient spin excitation dynamics and superconducting pairing far from equilibrium.