Optical properties along the c-axis of YBa2Cu3O6+x, for x = 0.50 → 0.95 evolution of the pseudogap

摘要: Abstract The reflectance of high-quality, unpolished single crystals YBa2Cu3O6+x, for the doping range x = 0.50 → 0.95, has been measured with radiation polarized along c-axis from ≈ 50 cm−1 to 5000 between 10 K and 300 K. In highly doped (x 0.95) material, normal-state conductivity shows a metallic response. For intermediate dopings 0.85 0.90) is no longer metallic, increasing temperature, low 0.80) this behavior clearly seen be caused by broad pseudogap at 290 cm−1, which develops well above Tc. superconducting state, in optimally gap-like depression below Tc but there residual very frequency indicating either an anisotropic gap, or gap nodes. underdoped materials superconductivity-induced changes are harder see, it appears that weight condensate originates frequencies much higher than conventional weak-coupling BCS value 3.5kBTc.