Charge-induced vortex lattice instability

It has been predicted that superconducting vortices should be electrically charged and that this effect is particularly enhanced for high-temperature superconductors1,2. Hall effect3 and nuclear magnetic resonance (NMR) experiments4 suggest the existence of charge accumulation in the vortex core, 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 a sufficiently high magnetic field if there is charge trapped on the vortex core. Our NMR measurements of the magnetic fields generated by vortices in Bi2Sr2CaCu2O8+y single crystals5 provide evidence for an electrostatically driven vortex lattice reconstruction with the magnitude of charge on each vortex pancake of ∼2 × 10−3e, depending on doping, in line with theoretical estimates1,6. The behaviour of quantized vortices in high-temperature superconductors affects many of their applications ranging from high-current-carrying wires7 to electronic devices8. Effective performance requires that the vortices be stable because their dynamics lead to dissipation originating from the electronic excitationswithin the vortex cores. Effort to understand the interactions between vortices has been focused on the circulating supercurrents that are characteristic of the vortex and generate local magnetic fields9. However, if the vortices are electrically charged there will also be an electrostatic interaction, possibly relevant to vortex stability. We have carried out model calculations showing that if vortices trap electrical charge, then theAbrikosov vortex lattice becomes unstable in sufficiently high magnetic fields where the magnetic interactions diminish and the electrostatics dominate. Our NMR experiments confirm the existence of a magnetic-field-induced instability in the vortex structure of the highly anisotropic superconductor Bi2Sr2CaCu2O8+y (Bi2212). A strong magnetic field normal to the conduction plane, H ‖ c , of Bi2212 penetrates in the form of quantized flux bundles, called pancake vortices5. They interact magnetically, with a repulsive interaction for pancakes within a plane, but attractive if they lie in different planes. The attractive force is responsible for aligning the vortex cores, one above the other, thereby forming flux lines as indicated in Fig. 1. Perfect alignment is called the Abrikosov configuration. However, the average attractive force decreases9 with increasing field as the vortex density increases and as the magnetic field modulations from nearby vortex supercurrents cancel each other more effectively. In contrast, for charged vortex cores, the electrostatic force between pancakes on different planes increases at short range. A complete picture of the balance of these forces requires that the nearby stacks of vortices be taken into account. The calculated cost in magnetic energy for displacing an entire plane of vortices has been calculated, relative to those in all other planes9. We follow this approach and compare the magnetic energy with