DIRECT MEASUREMENT OF THE ANISOTROPY OF THE RESISTIVITY IN THE A-B PLANE OF TWIN-FREE, SINGLE-CRYSTAL, SUPERCONDUCTING YBA2CU3O7-DELTA

We have measured the resistivity tensor in one nearly twin-free crystal and one twin-free crystal of YBa2Cu3O7-. The first crystal was grown with a large twin-free region. We removed the twins in the second crystal by applying a uniaxial stress. Using a modified Montgomery technique, we measured the electrical resistivities in all three crystal directions and found them to be linear in temperature above the superconducting transition temperature Tc. Our results for a and b at room temperature are among the lowest that have been reported in the literature, indicating that our samples are of high quality. The ratio a/b is independent of temperature between 150 and 275 K, and its value, 2.2 0.2, indicates that the Cu-O chains contribute 60% of the current when the electric field is parallel to them, with the rest of the current being contributed by the Cu-O planes. This result, at zero frequency, is in good agreement with the recent conductivity at infrared frequencies obtained by Schlesinger et al. © 1990 The American Physical Society.