Excitonicn-string in linear chains: Electronic structure and optical properties

Abstract

The electronic structure and the optical properties of an excitonic n-string which is a bound state of n Frenkel excitons (n = 2, 3, . . . ) are theoretically clarified. The binding mechanism may be attributed to the electrostatic dipolar interaction among the Frenkel excitons, which is in contrast to the formation mechanism of the otherwise analogous excitonic molecules in a system of Wannier excitons; it makes it possible to form bound states of more than two Frenkel excitons. The effects of the n-string states on the electronic structure and optical properties are studied. The two-photon absorption and the differential transmission spectra are shown to depend strongly on the direction of the induced static dipole moment, which determines whether the interaction between excitons is attractive or repulsive.

Photogenerated holon-doublon cluster states in strongly correlated low-dimensional electron systems

“…As shown before, although a holon and doublon are not bound or weakly bound in the HDP state, holons and doublons are strongly bound and the charge fluctuation arising from their relative motion is small in all the HDC states. This is in contrast to the cases of the biexciton in conventional semiconductors 3,4 and the exciton string in the organic charge-transfer solid, 5,6,8,9 where the binding energy of two excitons is much smaller than that of an electron and a hole in an exciton. This characteristic feature can be understood by considering the binding energy of a holon or a doublon arising from the ICI term V P m ; it is V in the HDP, and it is 2V in the HDCs in the 2D square lattice.…”

“…In the conventional semiconductors, 3,4 and also in the novel charge-transfer solids where the exciton string is observed, 5,6,8,9 the binding of excitons is due to the direct Coulomb interaction between the excitons. When excitons are aggregated, the Coulomb interaction energy decreases and the kinetic energy of the photogenerated charges increases.…”

“…3,4 The bound states of more than two excitons ͑exciton strings͒ have been found only in some quasi-1D organic chargetransfer solids. [5][6][7][8][9][10][11] An electron-hole pair is strongly bound to form an exciton in this case, and this is essential for the formation of the exciton string. It should be emphasized that the HDC states have a quite unique charge aggregation mechanism.…”

Pump–probe spectrum of molecular assemblies of arbitrary structure and dimension

“…Among the systems arousing most interest are J aggregates of cyanine dyes, Langmuir-Blodgett monolayers, and biomolecular systems such as antenna complexes consisting of chlorophyll molecules. Recently, many theoretical [4][5][6][7][8][9][10][11][12][13][14][15] and experimental [16][17][18][19][20][21][22][23][24] studies have been devoted to the pump-probe spectrum of these systems. In the weak-pump limit, this is a third-order nonlinear optical technique, which allows one to probe transitions between oneexciton states and two-exciton states.…”

Excitonic strings in one-dimensional organic compounds

“…Only a few theoretical investigations of excitonic strings in organic compounds have been done [4][5][6][12][13][14][15][16][17][18]. Most of them are based on exact diagonalizations of small clusters using different kinds of model Hamiltonians depending on the system under consideration [4][5][6]13].…”