Zeeman-perturbed 63Cu nuclear quadrupole resonance study of vortex state of YBa2Cu3O7-δ

We report a Cu-63 nuclear quadrupole resonance (NQR) study of the vortex state for all aligned polycrystalline sample of a slightly overdoped high-T-c superconductor YBa2Cu3O7-delta (T-c similar to 92 K) at a low magnetic field of 96 mT along the c axis, near a lower critical field H-cl. We observed the frequency distribution of the nuclear spin-lattice relaxation time T-63(1) in a Zeeman-perturbed Cu-63 NQR spectrum below T-c. The characteristic behavior of I/T-63(1) with respect to temperature and frequency suggests the role of antiferromagnetic spin fluctuations in the Doppler-shifted quasiparticle energy spectrum inside and outside vortex cores.