Localized states in the Mott insulator -(BEDT-TTF)2Cu[N(CN)2]Cl as probed by photoluminescence
Abstract
We compare the photoluminescence spectra of the low-temperature Mott insulator (TMIT=40 K) with spectra of metallic -(BEDT-TTF)2Cu[N(CN)2]Br, which is superconducting below Tc=11.8 K, in the temperature range between 300 and 20 K. In the Mott insulating state of -(BEDT-TTF)2Cu[N(CN)2]Cl we observe a luminescence band at 1.95 eV due to the recombination of an exciton created by a HOMO-LUMO optical excitation. This luminescence is quenched both in the high-temperature bad metal state of -(BEDT-TTF)2Cu[N(CN)2]Cl and in metallic -(BEDT-TTF)2Cu[N(CN)2]Br. The observation of the luminescence of an exciton provides evidence for the local character of excitations in the Mott insulating state.
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