OPTICAL CONDUCTIVITY IN THE T-J MODEL - SLAVE-BOSON, LARGE-N TECHNIQUE

We study the real part of the optical conductivity in the t-J model using the slave-boson technique and the large-N expansion to the next-to-leading order in 1/N. The conductivity falls off at a slower rate than predicted by the Drude theory due to the coupling to the low-energy spin excitation. The absorptions from the mid-infrared (MIR) range to higher frequency (approximately 1 eV) arise from the incoherent motion of the charge carrier. We compare our results to finite-cluster exact-diagonalization studies and to experimental studies in the copper oxide system.