Superconducting energy gap in domain boundaries of melt textured YBa2Cu3O7 from low magnetic field ultrasonic measurements

Since the discovery of high T_c superconductors, researchers have attempted to measure the superconducting energy gap and its temperature dependence using ultrasonic techniques. Although several interesting effects have been discovered, it has not yet been possible to measure the gap ultrasonically, until now. It is possible to deduce this gap from recent measurements of attenuation and velocity changes observed at the penetration field of the domain boundaries of a melt textured sample of YBa₂Cu₃O₇. A relaxation model is used to determine a relaxation time which depends on the density of excitations in the superconducting state which in turn depends on the superconducting energy gap. From this relation a BCS temperature dependence is evaluated for the energy gap