Superconducting Vortex-Charge Measurement Using Cavity Electromechanics

As the magnetic field penetrates the surface of a superconductor, it results in the formation of flux vortices. It has been predicted that the flux vortices will have a charged vortex core and create a dipolelike electric field. Such a charge trapping in vortices is particularly enhanced in high-T_c superconductors (HTS). Here, we integrate a mechanical resonator made of a thin flake of HTS Bi₂Sr₂CaCu₂O_8+δ into a microwave circuit to realize a cavity-electromechanical device. Due to the exquisite sensitivity of cavity-based devices to the external forces, we directly detect the charges in the flux vortices by measuring the electromechanical response of the mechanical resonator. Our measurements reveal the strength of surface electric dipole moment due to a single vortex core to be approximately 30 |e|a_B, equivalent to a vortex charge per CuO₂ layer of 3.7 × 10^-2|e|, where a_B is the Bohr radius and e is the electronic charge.