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

TL;DR

This study uses $^{63}$Cu NQR to investigate the vortex state in an overdoped high-$T_c$ superconductor, revealing the influence of antiferromagnetic spin fluctuations on quasiparticle excitations near the vortex cores.

Contribution

It provides the first detailed $^{63}$Cu NQR analysis of the vortex state in YBa$_2$Cu$_3$O$_{7- heta}$, highlighting the role of spin fluctuations in the quasiparticle spectrum.

Findings

Frequency distribution of $^{63}T_1$ observed below $T_c$

Antiferromagnetic spin fluctuations affect quasiparticle energies

Significant role of spin fluctuations inside and outside vortex cores

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$_{7-\delta}$ ($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.