Ultrabosonic behavior in photoexcited one-dimensional Mott insulators in the region of weak intersite Coulomb interaction

This paper reports a unique behavior expected for the optical excitations in one-dimensional Mott insulators. When the intersite Coulombic attraction does not work between two elementary charge excitations, i.e., a doublon and a holon, the lowest optical excitations are described as an unbound pair of them, still having finite mutual correlation due to the forbidden double occupancy on the same site. We find that, in such a situation, the pairs obey a particle statistics that exceeds that of ordinary bosons. This feature appears most directly in the enhancement factor of the matrix element for the pair photocreation. We discuss the possible mechanism for this ultrabosonic behavior and also demonstrate that this behavior is maintained even if we include a small amount of interiste Coulomibic interaction. Lastly, this enhancement factor almost coincides with that for ordinary bosons when the degree of the intersite interaction exceeds a certain value that switches on the formation of a bound doublon-holon pair.