Abstract
The c axis reflectance of high-quality single crystals of has been measured over a wide range of temperatures and frequencies. The x=0.70 crystal has a pseudogap in the conductivity at 200 which is present at room temperature. The gap deepens gradually as the temperature is lowered to 10 K with no discontinuity at . In contrast, crystals with x=0.95 show no gap in the normal state and their superconducting state is characterized by low-lying states. These observations are consistent with phase diagrams proposed to explain NMR and neutron data.
- Received 31 March 1993
DOI:https://doi.org/10.1103/PhysRevLett.71.1645
©1993 American Physical Society