Abstract
We present broadband infrared ellipsometry measurements of the -axis conductivity of underdoped (, Nd, and La) single crystals. Our data show that separate energy scales are underlying the redistributions of spectral weight due to the normal state pseudogap and the superconducting gap. Furthermore, they provide evidence that these gaps do not share the same electronic states and do not merge on the overdoped side. Accordingly, our data are suggestive of a two gap scenario with a pseudogap that is likely extrinsic with respect to superconductivity.
- Received 23 April 2007
DOI:https://doi.org/10.1103/PhysRevLett.100.177004
©2008 American Physical Society