Mottness in High-Temperature Copper-Oxide Superconductors

TL;DR

This paper discusses how high-temperature copper-oxide superconductors deviate from traditional Fermi liquid theory, highlighting experimental evidence of new degrees of freedom and a theoretical model involving a charge 2e bosonic field that explains key phenomena.

Contribution

It introduces a theoretical framework incorporating a charge 2e bosonic field to explain non-Fermi liquid behavior and the emergence of the charge gap and antiferromagnetism in cuprates.

Findings

Experimental evidence of excess low-energy states per electron.

Identification of a charge 2e bosonic field as a new degree of freedom.

Explanation of the charge gap and antiferromagnetism at half-filling.

Abstract

The standard theory of metals, Fermi liquid theory, hinges on the key assumption that although the electrons interact, the low-energy excitation spectrum stands in a one-to-one correspondence with that of a non-interacting system. In the normal state of the copper-oxide high-temperature superconductors, drastic deviations from the Fermi liquid picture obtain, highlighted by a pseudogap, broad spectral features and $T-$ linear resistivity. This article focuses on the series of experiments on the copper-oxide superconductors which reveal that the number of low-energy addition states per electron per spin exceeds unity, in direct violation of the key Fermi liquid tenet. These experiments point to new degrees of freedom, not made out of the elemental excitations, as the key mechanism by which Fermi liquid theory breaks down in the cuprates. A recent theoretical advance which permits an explicit integration of the high energy scale in the standard model for the cuprates reveals the source of the new dynamical degrees of freedom at low energies, a charge 2e bosonic field which has nothing to do with pairing but rather represents the mixing with the high energy scales. We demonstrate explicitly that at half-filling, this new degree of freedom provides a dynamical mechanism for the generation of the charge gap, antiferromagnetism in the insulating phase and explains many of the anomalies in the normal state of the cuprates.