Optical Study of Spin/Charge Stripe Order Phase in (La,Nd,Sr)2CuO4

Optical spectra of the spin/charge stripe order phase, La1.6−xNd0.4SrxCuO4 (LNSC) have been investigated for x=0.10,0.12,0.15 and 0.20, compared with the spectra of Nd-free (La,Sr)2CuO4. For E//c, a sharp plasma edge for superconducting carriers cannot be observed in LNSC within our covering frequency range down to 40 cm−1. This implies that the stripe charge order strongly suppresses the superfluid density and/or the Josephson coupling strength between the layers. For E//ab, optical conductivity is substantially suppressed over a wide frequency range even at room temperature, while no appreciable spectral change takes place at the structural (LTO-LTT) phase transition temperature Td2. The former fact is indicative of a strong stripe fluctuation well above Td2. The metallic ω- and T-dependencies of optical conductivity in LNSC are in contrast to the low ω conductivity at dc and in the microwave region, which exhibits a weak semiconducting T-dependence below Td2. This suggests that some disorder effect dominates in the stripe charge dynamics in the very low ω region.