Neglected $U(1)$ phase in the Schroedinger representation of quantum mechanics and particle number conserving formalisms for superconductivity

TL;DR

This paper introduces a particle-number conserving formalism for superconductivity by incorporating a neglected $U(1)$ phase as a gauge field, leading to different predictions from the standard theory and aligning better with experimental results.

Contribution

The paper reveals the importance of a neglected $U(1)$ phase in superconductivity, reformulating the theory to conserve particle number and correcting previous approximations.

Findings

Revised Josephson relation with capacitance contribution

Standard theory's agreement with experiments improved by the new formalism

Dissipative quantum phase transition predicted in standard theory is absent in the new formalism

Abstract

Superconductivity is reformulated as a phenomenon in which a stable velocity field is created by a $U(1)$ phase neglected by Dirac in the Schroedinger representation of quantum mechanics. The neglected phase gives rise to a $U(1)$ gauge field expressed as the Berry connection from many-body wave functions. The inclusion of this gauge field transforms the standard particle-number non-conserving formalism of superconductivity to a particle-number conserving one with many results of the former unaltered. In other words, the new formalism indicates that the current standard one is an approximation that effectively takes into account this neglected $U(1)$ gauge field by employing the particle-number non-conserving formalism. Since the standard and new formalisms are physically different, conflicting results are predicted in some cases. We reexamine the Josephson relation and show that a capacitance contribution of the Josephson junction to the $U(1)$ phase is missing in the standard formalism, and inclusion of it indicates that the standard theory actually does one agree with the experiment while the new one does. It is also shown that the dissipative quantum phase transition in Josephson junctions predicted in the standard theory does not exit in the new one in accordance with the recent experimental result.