Emergence of nodal Bogoliubov quasiparticles across the transition from the pseudogap metal to the d-wave superconductor

TL;DR

This paper models the pseudogap state in cuprates as a metal with Fermi surfaces that violate traditional electron count rules, and shows that upon transitioning to a d-wave superconductor, gapless nodal Bogoliubov quasiparticles emerge at four points in the Brillouin zone.

Contribution

It introduces a theoretical framework describing the emergence of nodal Bogoliubov quasiparticles across the pseudogap to superconductor transition in cuprates.

Findings

Gapless Bogoliubov quasiparticles appear at four nodal points in the Brillouin zone.

Nodal quasiparticles emerge even in electron-doped cases with only electron pockets.

The transition involves a Higgs mechanism within an SU(2) gauge symmetry context.

Abstract

We model the pseudogap state of the hole- and electron-doped cuprates as a metal with hole and/or electron pocket Fermi surfaces. In the absence of long-range antiferromagnetism, such Fermi surfaces violate the Luttinger requirement of enclosing the same area as free electrons at the same density. Using the Ancilla theory of such a pseudogap state, we describe the onset of conventional $d$-wave superconductivity by the condensation of a charge e Higgs boson transforming as a fundamental under the emergent SU(2) gauge symmetry of a background $\pi$-flux spin liquid. In all cases, we find that the $d$-wave superconductor has gapless Bogoliubov quasiparticles at 4 nodal points on the Brillouin zone diagonals with significant velocity anisotropy, just as in the BCS state. This includes the case of the electron-doped pseudogap metal with only electron pockets centered at wavevectors $(\pi, 0)$, $(0, \pi)$, and an electronic gap along the zone diagonals. Remarkably, in this case too, gapless nodal Bogoliubov quasiparticles emerge within the gap at 4 points along the zone diagonals upon the onset of superconductivity.