Charged vortices in high temperature superconductors probed by nuclear magnetic resonance Original Research Article

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 YBa2Cu3O7 the vortex is negatively charged by trapping electrons, while in underdoped YBa2Cu4O8 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.