A-B ANISOTROPY OF THE NORMAL-STATE RESISTIVITY OF UNTWINNED YBA2CU3O7-DELTA

The a-b anisotropy of the normal-state resistivity a/b of untwinned YBa2Cu3O7- has been studied on six crystals using the Montgomery method. a/b increases with increasing temperature and reaches a (sample-dependent) value of 1.21.85 near room temperature. The wide variation of this value is attributed to the high sensitivity of the chain resistance to oxygen disorder. The temperature dependence of a/b can be modeled by a parallel circuit of metallic chains and superconducting planes with excess conductivity due to superconducting fluctuations in the planes at temperatures below 150 K. © 1990 The American Physical Society.