Phenomenological model of protected behavior in the cuprate superconductors

TL;DR

This paper presents a phenomenological model explaining the protected magnetic behavior in the pseudogap state of cuprate superconductors, highlighting the roles of spin liquids, Fermi liquids, and quantum critical points.

Contribution

It extends previous magnetic scaling work to 1-2-3 cuprates, proposing a model involving spin liquids and Fermi liquids, and identifies two quantum critical points influencing superconductivity.

Findings

Identification of two quantum critical points at doping levels ~0.05 and ~0.22.

Evidence for a mixture of insulating spin liquid and Fermi liquid in the pseudogap state.

Magnetic interactions between quasiparticles and spin liquid excitations induce d-wave superconductivity.

Abstract

By extending previous work on the scaling of low frequency magnetic properties of the 2-1-4 cuprates to the 1-2-3 materials, we arrive at a consistent phenomenological description of protected behavior in the pseudogap state of the magnetically underdoped cuprates. Between zero hole doping and a doping level of $\sim 0.22$ it reflects the presence of a mixture of an insulating spin liquid that produces the measured magnetic scaling behavior and a Fermi liquid that becomes superconducting for doping levels $x>0.06$. Our analysis suggests the existence of two quantum critical points, at doping levels, $x \sim 0.05$ and $x \sim 0.22$, and that d-wave superconductivity in the pseudogap region arises from quasiparticle-spin liquid interaction, i.e. magnetic interactions between quasiparticles in the Fermi liquid induced by their coupling to the spin liquid excitations.