H. Ezaki et al., EXCITONIC N-STRING IN LINEAR-CHAINS - ELECTRONIC-STRUCTURE AND OPTICAL-PROPERTIES, Physical review. B, Condensed matter, 50(15), 1994, pp. 10506-10515
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 th
e electrostatic dipolar interaction among the Frenkel excitons, which
is in contrast to the formation mechanism of the otherwise analogous e
xcitonic molecules in a system of Wannier excitons; it makes it possib
le to form bound states of more than two Frenkel excitons, The effects
of the n-string states on the electronic structure and optical proper
ties are studied. The two-photon absorption and the differential trans
mission spectra are shown to depend strongly on the direction of the i
nduced static dipole moment, which determines whether the interaction
between excitons is attractive or repulsive.