Superconductors strongly repel a magnetic field. This phenomenon, known as the Meissner effect, is the scientific basis for the magnetically levitated (maglev) superconducting trains, which can move at a speed of 500 km/h (310 mi/h). According to electromagnetic theory, electric and magnetic fields are intricately related. Thus, the interaction between superconductors and an electric field is of great interest. Fritz London first studied the issue in 1935 and proposed that superconductors and conventional conductors might react to electric fields differently. However, due to the difficulties associated with these types of experiments, this issue remains controversial and unresolved. The recent discovery of the formation of superconducting balls in a strong electric field illustrates the rich physics of this area.