Producing coherent excitations in pumped Mott antiferromagnetic insulators

Nonequilibrium dynamics in correlated materials has attracted attention due to the possibility of characterizing, tuning, and creating complex ordered states. To understand the photoinduced microscopic dynamics, especially the linkage under realistic pump conditions between transient states and remnant elementary excitations, we performed nonperturbative simulations of various time-resolved spectroscopies. We used the Mott antiferromagnetic insulator as a model platform. The transient dynamics of multiparticle excitations can be attributed to the interplay between Floquet virtual states and a modification of the density of states, in which interactions induce a spectral weight transfer. Using an autocorrelation of the time-dependent spectral function, we show that resonance of the virtual states with the upper Hubbard band in the Mott insulator provides the route towards manipulating the electronic distribution and modifying charge and spin excitations. Our results link transient dynamics to the nature of many-body excitations and provide an opportunity to design nonequilibrium states of matter via tuned laser pulses.

Figure 1

Schematic cartoon illustrating various time regions during a pump process.

Figure 2

Instantaneous magnetic fluctuation $\langle {\widehat{m}}_z^2\rangle \left(t\right)$. Various curves represent different pump intensities but fixed frequency ($\mathrm{\Omega }=4.4t_h$) and width (${\sigma }_t=3.0t_h^{-1}$). The phase-averaged magnetic moments are shown in the central thick curves. The gray curve represents the pump field.

Figure 3

Snapshots of dynamical spin $S(q,\omega ;t)$ (upper panels), charge (middle panels) structure factors $N(q,\omega ;t)$, and single-particle spectral function $A(k,\omega ;t)$ (lower panels) during the pump at $t=-10$, $-5$, 0, 5, and $10t_h^{-1}$. Those open markers denote the peak positions at various momenta. The top insets indicate the current time (red dot) compared to the pulsed laser.

Figure 4

(a)–(e) Snapshots of autocorrelation $\mathcal{C}(k,\mathrm{\Delta }\omega ;t)$ for $k=0$. The solid/dashed/dotted lines denote the first/second/third Floquet frequencies as a function of pump. The time frames are the same as those in Fig. 3.

Figure 5

Final photoinjected energies (open circles) (a) at the beginning ($t=-5t_h^{-1}$) and (b) after the pump ($t=10t_h^{-1}$) as a function of pump fluences, at $\mathrm{\Omega }=2,4,7t_h$. The colored straight lines represent a first-, second-, and third-order polynomial fitting.

Figure 6

(a) Comparison of finite-temperature spectra $S^{\mathrm{eq}}{(\pi ,\omega )|}_T$ (red) with the nonequilibrium $S^{\mathrm{neq}}(\pi ,\omega ;t)$ (blue shaded region) at $t=10t_h^{-1}$ after pump. The effective temperature is determined through the maximum correlation principle shown in the inset. (b) Evolution of average energy $E\left(t\right)$ (blue solid line) and temperature dependence of equilibrium energy $E\left(T\right)$ (green dashed line). The pump pulse in both figures is set as Fig. 3.

Figure 7

The spin (upper panels) and charge (lower panels) structure factors evaluated by adiabatic Floquet approximation at an eight-site chain. The top insets indicate the steady pump field to mimic the time evolution.

Figure 8

(a)–(c) Evolution of $A(0,\omega )$ for various pump frequency ${\omega }_0$ with a fixed pump amplitude ($A_0=1.2$). (d)–(f) Evolution of $A(0,\omega )$ for various pump amplitude $A_0$ with a fixed pump frequency (${\omega }_0=4.4t_h$). The pump width is fixed for all these figures (${\sigma }_t=3.0t_h^{-1}$). The red arrows guide the eye for the Floquet frequencies, while the dotted white lines denote the Floquet estimated spinon and holon branches.