The Improved Electromagnetic Equations and Superconductivity
  In this paper the macroscopic condition for dissipationless current in conductors is investigated and a set of improved electromagnetic equations are proposed. With these equations we show that the dissipation is particularly relative to free volume charges in conductors that originate from self-Hall-effect. The steadily normal current coexists with free volume charges and the steadily superconducting current doesn't. Zero Hall coefficient is a candidate condition for nonexistence of free volume charges in conductors and a possible mechanism is exciton conduction or electron-hole pairing. 
Weilong She
physics.class-ph cond-mat.supr-con