Abstract
We compare the photoluminescence spectra of the low-temperature Mott insulator -(BEDT–TTF)Cu[N(CN)]Cl ( K) with spectra of metallic -(BEDT–TTF)Cu[N(CN)]Br, which is superconducting below K, in the temperature range between 300 and 20 K. In the Mott insulating state of -(BEDT–TTF)Cu[N(CN)]Cl we observe a luminescence band at 1.95 eV due to the recombination of an exciton created by a highest occupied molecular orbital–lowest unoccupied molecular orbital optical excitation. This luminescence is quenched both in the high-temperature bad metal state of -(BEDT–TTF)Cu[N(CN)]Cl and in metallic -(BEDT–TTF)Cu[N(CN)]Br. The observation of the luminescence of an exciton provides evidence for the local character of excitations in the Mott insulating state.
- Received 7 March 2013
DOI:https://doi.org/10.1103/PhysRevB.88.115109
©2013 American Physical Society