APPLICATION OF THE POLARON-TRANSPORT THEORY TO SIGMA(OMEGA) IN TL2BA2CA1-XGDXCU2O8, YBA2CU3O7-DELTA, AND LA2-XSRXCUO4

We analyze the frequency-dependent photoinduced infrared conductivity, P(), obtained from photoinduced absorption measurements of the insulators Tl2Ba2Ca0.98Gd0.02Cu2O8, YBa2Cu3O6.3, and La2CuO4 in terms of PT() calculated from nonadiabatic polaron-transport theory. The calculated PT() is in good agreement with the experimental P() in the midinfrared. We also compare P() with the infrared conductivity, (), of the high-Tc superconductors Tl2Ba2CaCu2O8, YBa2Cu3O7, and La1.85Sr0.15CuO4. The similar spectral shape and systematic trends in both P() and () indicate that the carriers in the concentrated (metallic) regime retain much of the character of the carriers in the dilute (photoexcited) regime. Together, these results imply that in the superconducting cuprates and in their parent insulators, the carriers are polarons dressed with a phonon polarization cloud. © 1990 The American Physical Society.