63Cu nuclear relaxation study in the superconducting mixed state in YBa 2Cu 3O 7: Magnetic excitation at low temperature

Abstract

63Cu spin-lattice relaxation rate 63(1/ T 1) at the CuO 2 plane site in YBa 2Cu 3O 7 has been measured under the strong magnetic field parallel and perpendicular to the c-axis in the oriented powder. The relaxation rate, 1/ T 1 in the mixed state at low temperatures, which has revealed almost a linear magnetic-field dependence, is dominated by the spin-diffusion process to the vortex cores. A most prominent finding is that the magnetic excitation in the normal vortex core is described in terms of T 1 T=const. law below about 10K. From the estimation of 1/ T 1 in the magnetic field induced normal state in YBa 2Cu 3O 7, it is demonstrated that the normal state could be treated within the framework of the Fermi liquid picture at low temperatures, if the superconductivity were destroyed by the magnetic field.