ELECTRON-SPIN-RESONANCE IN SUPERCONDUCTING MELT-TEXTURED GDBA2CU3O7-DELTA - EVIDENCE AGAINST UNIFORM FLUX ENTANGLING

Electron-spin-resonance measurements on melt-textured GdBa2Cu3O7-delta as a function of the angle between the rf and static magnetic fields reveal an angular-dependent response that is not consistent with recent proposals that flux entangling is responsible for isotropic or near-isotropic ab-plane resistivity or suppression of flux flow. Microwave surface-resistance data suggest near isotropy at low temperatures, while the resonance intensity varies approximately as sin2(phi), where phi is the angle between the static field H and H(rf) with both in the ab plane; this is the dependence expected for resonance in normal materials. Uniform flux entangling would lead to an isotropic resonance intensity.