Theory of spin excitations in undoped and underdoped cuprates

TL;DR

This paper explores the magnetic properties of underdoped cuprates using gauge theory, showing how gauge fluctuations restore antiferromagnetic correlations that mean field theories fail to capture, and analyzing related models.

Contribution

It introduces a gauge theory framework to better understand antiferromagnetic correlations in underdoped cuprates, highlighting the role of gauge fluctuations and their impact on magnetic ordering.

Findings

Gauge fluctuations restore antiferromagnetic correlations.

1/N perturbation theory demonstrates dynamical mass generation.

Enhanced correlations without symmetry breaking in coupled gauge-bose systems.

Abstract

We consider the magnetic properties of high Tc cuprates from a gauge theory point of view, with emphasis on the underdoped regime. Underdoped cuprates possess certain antiferromagnetic correlations, as evidenced, for example, by different temperature dependence of the Cu and O site NMR relaxation rates, that are not captured well by slave boson mean field theories of the t-J model. We show that the inclusion of gauge fluctuations will remedy the deficiencies of the mean field theories. As a concrete illustration of the gauge-fluctuation restoration of the antiferromangetic correlation and the feasibility of the 1/N perturbation theory, the Heisenberg spin chain is analyzed in terms of a 1+1D U(1) gauge theory with massless Dirac fermions. The 1/N-perturbative treatment of the same gauge theory in 2+1D (which can be motivated from the mean field pi-flux phase of the Heisenberg model) leads to a dynamical mass generation corresponding to an antiferromagnetic ordering. On the other hand, it is argued that in a similar gauge theory with an additional coupling to a Bose (holon) field, symmetry breaking does not occur, but antiferromagnetic correlations are enhanced, which is the situation in the underdoped cuprates.