Superconductivity emerging near U(1) topological critical point and the strange metal phase in cuprates

Abstract

Topological excitations are examined to establish an effective theory of the superconducting state evolving from the Mott insulator in high- T c cuprates. We emphasise the Coulomb interaction U that is governed by the electromagnetic U(1) compact group. The results are obtained for the layered t− t′− t ⊥− U− J system of strongly correlated electrons relevant for cuprates. We exploit the U(1) instanton phase field configurations for the cuprate phase diagram which displays the “hidden” quantum critical point covered by the superconducting lobe in addition to a sharp crossover between a compressible normal “strange metal” state and a region characterized by a vanishing compressibility, which marks the Mott insulator. The existence of robust topological quantum numbers explains the stability against small perturbation of the system and attributes to the topological “quantum protectorate” as observed in strongly correlated systems.