Dynamics of photoexcited states in one-dimensional dimerized Mott insulators

Dynamical properties of photoexcited states are theoretically studied in a one-dimensional Mott insulator dimerized by the spin-Peierls instability. Numerical calculations combined with a perturbative analysis have revealed that the lowest photoexcited state without nearest-neighbor interaction corresponds to an interdimer charge transfer excitation that belongs to dispersive excitations. This excited state destabilizes the dimerized phase, leading to a photoinduced inverse spin-Peierls transition. We discuss the purely electronic origin of midgap states that are observed in a latest photoexcitation experiment of an organic spin-Peierls compound, K-TCNQ (potassium-tetracyanoquinodimethane).

Figure 1

Dimerized 1D system with alternating transfer integrals. The thick lines correspond to the larger transfer integrals, and the thin lines to the smaller ones.

Figure 2

Optical conductivity spectra in the 1D dimerized Hubbard model for $U∕t=10$ and 15. The insets show results of nearly decoupled systems $(\delta =0.95)$.

Figure 3

Adiabatic potentials $E_i\left(\delta \right)$ of three states ($i=0$, $A$, and $B$) for the $N=8$ system.

Figure 4

Schematic picture of the ground state, the intradimer and the interdimer CT states. The ellipses show the singlet dimer states, and the up (down) arrows are electrons with up (down) spins.

Figure 5

Intradimer and interdimer CT states, and their excitation energies for $U∕t⪢1$. The spin indices in $\mid O_{\sigma }^3⟩$ and in $\mid E_{\overline{\sigma }}^1⟩$ are omitted.

Figure 6

Dynamics of excited dimers in the optically excited states. Effective transfer integrals for $\mid O^3⟩$ and $\mid E^1⟩$, and that for $\mid O^2⟩$ are very different as indicated.

Figure 7

Optical excitation energies. The symbols show the exact-diagonalization results, and the lines show the perturbative results.

Figure 8

Spin dimerization in the three states.

Figure 9

Optical conductivity spectra in the photoexcited state $\mid {\psi }_A⟩$ for $U∕t=15$.

Figure 10

Midgap and other relevant states. The energy differences are also shown for $U∕t⪢1$.

Figure 11

Dynamics of excited dimers in the midgap state. It contains a light “particle” $\mid E^1⟩$ and a heavy “particle” $\mid E^3⟩$.

Figure 12

Calculated energies and spectral intensities for the midgap states. The symbols show the results of the exact diagonalization of the Hamiltonian (2) and the lines denote the results of the first-order perturbation theory. The circles and the solid lines are for $\mid {\psi }_{\mathrm{mid}}^1⟩$, the squares and the dotted lines for $\mid {\psi }_{\mathrm{mid}}^2⟩$, and the triangles and the dashed lines for $\mid {\psi }_{\mathrm{mid}}^3⟩$.

Figure 13

Schematic picture of the relevant optical excitations for (a) $V=0$ and (b) finite $V$.