Structural Symmetry Breaking Drives Spontaneous Supercurrent and the Superconducting Diode Effect

Abstract

The origin of the spontaneous supercurrent in superconductors is theoretically identified. In the superconducting state, a lattice of alternating bipolaron and empty cells forms, distorted by shear stress from the metallic phase as structural symmetry breaking. Bipolarons are bound by a shallow attractive potential V₀ = V_{charge-density-wave} + U_c < 0, where U_c is the critical on-site Coulomb repulsion, on the order of milli-electron volts. When the transmission coefficient T ≈ 1 is achieved by overlap of bipolaron wave functions, coherent tunneling without reflection occurs, producing a spontaneous supercurrent density, \({{J}_{{{\text{spont}}}}} = 2en\sqrt {|{\kern 1pt} {{V}_{0}}{\text{|/}}{{m}_{0}}} \): V₀ acts as an internal electromotive force. This mechanism explains superconductivity, encompassing the zero resistance, Meissner effect even in the absence of the external magnetic field, and superconducting diode effect.