Absence of Orbital Currents in Superconducting YBa_2Cu_4O_8 Using a Zeeman-Perturbed Nuclear-Quadrupole-Resonance Technique

摘要

Zeeman perturbed nuclear quadrupole resonance was applied to evaluate weak magnetic fields in the context of orbital currents in cuprate superconductors. The magnetic environment of the barium atom in c-axis oriented powder samples of YBa_2Cu_4O)8 was investigated in the pseudogap phase at 90 K. No evidence for orbital currents was found: any static and dynamic field must be less than 0.07 and 0.7 mT, respectively.