Dynamical Coupling and Separation of Multiple Degrees of Freedom in a Photoexcited Double-Exchange System

We present a theory of ultrafast photoinduced dynamics in a spin-charge coupled system, motivated by pump-probe experiments in perovskite manganites. A microscopic picture for multiple dynamics in spin and charge degrees is examined. Real-time simulations are carried out by two complimentary methods. Our calculation demonstrates that electron motion governs a short-time scale where charge and spin dynamics are combined strongly, while, in a long-time scale controlled by spin relaxation, the charge sector does not follow the remarkable change in the spin sector. The present results are in contrast to a conventional double-exchange picture in equilibrium states.

Figure 1

(a) One-particle excitation spectra before pumping, (b) those at $\tau t=3$, and (c) those at $\tau t=10$. Momenta are changed from $\pi$ to 0 for the data from the top to the bottom. (d) Time dependence of optical absorption spectra.

Figure 2

Spin-correlation functions at several times.

Figure 3

Width of the in-gap band in one-particle excitation spectra $W$, spectral weight inside of the optical gap $D$, and NN spin-correlation function $K_S$. Data are subtracted by values at $\tau =0$, and are normalized by differences between the minimum and maximum values. We take $({\omega }_U,{\omega }_L)=(6.5,-1)$ and $({\omega }_U^{\prime },{\omega }_L^{\prime })=(4,0.5)$. The inset shows $K_S$ for several transfer integrals.

Figure 4

(a) NN spin-correlation function $K_S$ for several values of the relaxation constant ${\Gamma }_L$. The inset shows $K_S$ for the several transfer integrals $\alpha t$ and ${\Gamma }_L=0.002$. (b) Spin-correlation functions $S(0)$ for several ${\Gamma }_L$ (bold lines), and $S(\pi ,\pi )$ for ${\Gamma }_L=0.002$ (dotted line). The dotted arrows represent ${\tau }_L$. (c) Charge correlation function $N(\pi ,\pi )$ and NN charge correlation $K_N$.