On temperature dependence of DC and AC resistance of HTSC in normal state

Abstract The value and sign of the derivative ∂R/∂T in HTSC materials in the normal state are found to depend on the measurement frequency. Being of the metallic type at dc and low frequency, R(T) turns into the dependence of the semiconductive type and then again metallic, as the frequency increases. The phenomenon is observed at 10 3 − 10 8 Hz on ceramic, thin film and single crystal samples of different HTSC materials.