Charged vortices in high temperature superconductors probed by nuclear magnetic resonance

Abstract

We report an experimental evidence that a vortex in the high temperature superconductors traps a finite electric charge from the high resolution measurements of the nuclear quadrupole frequencies. In slightly overdoped YBa 2Cu 3O 7 the vortex is negatively charged by trapping electrons, while in underdoped YBa 2Cu 4O 8 it is positively charged by expelling electrons. The sign of the trapped charge is opposite to the sign predicted by the conventional BCS theory. Moreover, in both materials, the deviation of the magnitude of the charge from the theory is also significant.