Ultrafast Charge Recombination in a Photoexcited Mott-Hubbard Insulator

We present a calculation of the recombination rate of the excited holon-doublon pairs based on the two-dimensional model relevant for undoped cuprates, which shows that fast processes, observed in pump-probe experiments on Mott-Hubbard insulators in the picosecond range, can be explained even quantitatively with the multimagnon emission. The precondition is the existence of the Mott-Hubbard bound exciton of the $s$-type. We find that its decay is exponentially dependent on the Mott-Hubbard gap and on the magnon energy, with a small prefactor, which can be traced back to strong correlations and consequently large exciton-magnon coupling.

Figure 1

Holon-doublon pair binding energy ${ϵ}_b$ vs $J$. The plotted results are for the $s$-type g.s. for $N=18$, 20, 26 lattices with $V=0$ as well as the for $V=1$ on a $N=26$ lattice.

Figure 2

Exciton recombination rate $\Gamma$ vs gap $\Delta$ for $J=0.4$ and different planar systems with $N=20$, 24, 26 sites. Results are smoothed with $\delta =0.07$.

Figure 3

Exciton recombination rate $\Gamma$ vs (a) $\Delta /J$ and (b) $\Delta /J\ln (\Delta /te)$ for different $J=0.3$, 0.4, 0.6 as calculated for $N=26$ sites.

Figure 4

Deviations of bond energies for the holon-doublon pair g.s. relative to AFM g.s. in units of AFM g.s. bond energy, as calculated for the most probable pair configuration and $J=0.4$.