The Hall effect in untwinned single-crystal superconducting yttrium barium(2) copper(3) oxygen(7-y)

Abstract

We measured the Hall effect in untwinned single-crystal YBa$\sb2$Cu$\sb3$O$\sb{\rm 7-y}$, a high-T$\sb{\rm c}$ superconductor. The crystals were grown using a technique that we invented, in which untwinned domains are produced naturally without applying stress to the sample.

The Hall effect measurements were directed at understanding fluctuation phenomena just above T$\sb{\rm c},$ where small regions of a sample experience short-lived thermodynamic fluctuations into the superconducting state. Effects from these fluctuations appear in the temperature dependences of the Hall coefficient and conductivity as substantial deviations from the 1/T normal-state behavior. Because the original Fukuyama, Ebisawa, and Tsuzuki theory of the fluctuation-induced Hall effect is for an isotropic superconductor and YBa$\sb2$Cu$\sb3$O$\sb{\rm 7-y}$ is a layered material, we compared our data to an extended version. We calculated terms that were lacking and corrected mistakes in the literature to arrive at a complete and consistent theory for the effect of fluctuations on the Hall effect in a layered superconductor. From the fits of this theory to our data we were able to obtain fundamental information, such as the size of the superconducting coherence length and the nature of the coupling of the superconducting planes within the crystal structure of YBa$\sb2$Cu$\sb3$O$\sb{\rm 7-y}$.

Below T$\sb{\rm c}$, we obtained information about vortex motion from the Hall effect and magnetoresistance. For example, we found that the Hall resistivity changes sign over a certain range of magnetic field and temperature below T$\sb{\rm c}$, even in untwinned crystals. Thus this anomalous behavior, originally discovered in twinned samples, is not due to effects of twin planes.