Collective Density Wave Excitations in Two-leg Sr14-xCaxCu24O41 Ladders
22 August 2003
Raman measurements in the 1.5 - 20 cm -1 energy range were performed on single crystals of Sr14-xCaxCu24O41. A quasielastic scattering peak (QEP) which softens with cooling is observed in the polarization parallel to the ladder direction for samples with x=0, 8 and 12. the QEP is a Raman fingerprint of pinned collective density wave excitations screened by uncondensed carriers.
Our results suggest that transport in metallic samples, which is similar to transport in underdoped high-Tc cuprates, is driven by a collective electronic response.