Zeeman Perturbed ${}^{63}$Cu Nuclear Quadrupole Resonance Study of the Vortex State of YBa${}_2$Cu${}_3$O${}_{7-\hat{I}´}$

Abstract

We report a ${}^{63}$Cu nuclear quadrupole resonance (NQR) study of the vortex state for an aligned polycrystalline sample of a slightly overdoped high-$T_c$ superconductor YBa${}_2$Cu${}_3$O${}_{7-\hat{I}´}$ ($T_c\sim$92 K) at a low magnetic field of 96 mT along the c axis, near a lower critical field $H_{c1}$. We observed the frequency distribution of the nuclear spin-lattice relaxation time ${}^{63}{T}_1$ in the Zeeman-perturbed ${}^{63}$Cu NQR spectrum below $T_c$. The characteristic behavior of 1/${}^{63}{T}_1$, taking the minimum values with respect to temperature and frequency, indicates the significant role of antiferromagnetic spin fluctuations in the Doppler-shifted quasiparticle energy spectrum inside and outside vortex cores.

4 pages, 4 figures