Nuclear Magnetic Resonance Studies of the Effect of Vortices on the High Temperature Superconductor Yttrium Barium Copper Oxide

Abstract

Nuclear Magnetic Resonance in the material YBa2Cu3O 7 is strongly affected by the presence of magnetic vortices. The effects produced by the vortices can be used to gain knowledge about the physics of vortices and the physics of these materials. NMR nutation curves show that the vortices produce lossy (Ohmic) conduction in this material and greatly enhance the penetration depth over the London value. This enhancement is necessary to study crystal samples. The vortices induce supercurrents in the material which in turn enhance the density of states at the Fermi level. This enhancement, known as the Volovik Effect, can be observed in NMR as an increase in the spin-lattice relaxation rate as a function of frequency across the resonance line. The Volovik Effect was observed in both copper and oxygen in the plane of YBa2Cu3O7. The Volovik Effect was not able to be observed with sufficient precision to discriminate between various theories because it was obscured by other physical mechanisms within the sample studied.