It has been predicted that superconducting vortices should be electrically charged and that this effect is particularly enhanced for, high temperature superconductors.cite{kho95,bla96} Hall effectcite{hag91} and nuclear magnetic resonance (NMR) experimentscite{kum01} suggest the existence of vortex charging, but the effects are small and the interpretation controversial. Here we show that the Abrikosov vortex lattice, characteristic of the mixed state of superconductors, will become unstable at sufficiently high magnetic field if there is charge trapped on the vortex core. Our NMR measurements of the magnetic fields generated by vortices in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+y}$ single crystalscite{che07} provide evidence for an electrostatically driven vortex lattice reconstruction with the magnitude of charge on each vortex pancake of $mathbf{sim 2}$x$mathbf{10^{-3} e}$, depending on doping, in line with theoretical estimates.cite{kho95,kna05}
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