Higgs Criticality in a Two-Dimensional Metal
FIG. 1: the proposed phase diagram for the hole-doped cuprates, building on a theory for Higgs criticality for the optimal doping QCP. The lgebraic charge liquids (ACLs) have Fermi surfaces of spinless fermions which carry the electromagnetic charge: in the SU(2) ACL the Fermi surface is 'large' and is coupled to an emergent SU(2) gauge field, while in the U(1) ACL the Fermi surface is 'small' and coupled to an emergent U(1) gauge field. The fractionalized Fermi liquid (FL*) descends from the U(1) ACL by the binding of fermions to neutral spinons. The d-BDW is the d-form factor bond density wave, the d-SC is the d-wave superconductor, and the FL is the large Fermi surface Fermi liquid... [From See D. Chowdhury and S. Sachdev, "Higgs criticality in a two-dimensional metal," Dec 4, 2014, http://arxiv.org/pdf/1412.1086v1.pdf.]
In a new arXiv paper, grad student Debanjan Chowdhury and Prof. Subir Sachdev analyze a candidate theory for the strange metal near optimal hole-doping in the cuprate superconductors. The theory contains a quantum phase transition between metals with large and small Fermi surfaces, but the transition does not directly involve any broken global symmetries. The two metals have emergent SU(2) and U(1) gauge fields respectively, and the transition is driven by the condensation of a real Higgs field, carrying a finite lattice momentum and an adjoint SU(2) gauge charge. This Higgs field measures the local antiferromagnetic correlations in a 'rotating reference frame'. Chowdhury and Sachdev propose a global phase diagram around this Higgs transition, and describe its relationship to a variety of recent experiments on the cuprate superconductors.