Exciton-assisted low-energy magnetic excitations in a photoexcited Mott insulator on a square lattice

TL;DR

This study uses numerical simulations to reveal that photoexcited Mott insulators exhibit low-energy magnetic excitations facilitated by excitonic states, explaining recent experimental observations.

Contribution

It uncovers the role of excitonic states in generating low-energy magnetic excitations in photoexcited Mott insulators, a novel insight into their transient magnetic dynamics.

Findings

Low-energy magnetic signals emerge after photoexcitation.

Excitonic states at the absorption edge facilitate these excitations.

Results align with recent experimental observations in YBa₂Cu₃O₆.₁.

Abstract

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 pulse tuned for an absorption edge, new magnetic signals clearly emerge well below the 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 the low-energy spectral weight in a recent time-resolved two-magnon Raman scattering experiment for insulating YBa$_2$Cu$_3$O$_{6.1}$.