Spin-gap formation in cuprates: gauge theory

TL;DR

This paper uses gauge theory to analyze the phase diagram of cuprates, predicting the absence of a spin-gap in single-layer cuprates and its possible presence in bi-layer cuprates due to inter-layer pairing.

Contribution

It introduces a gauge-field framework to explain the differences in spin-gap behavior between single and bi-layer cuprates, emphasizing inter-layer pairing effects.

Findings

Single-layer cuprates lack a spin-gap due to gauge fluctuations.

Bi-layer cuprates exhibit a spin-gap likely caused by inter-layer fermion pairing.

Superconducting gaps in bi-layer cuprates may be nodeless in underdoped samples.

Abstract

We analyze the phase diagram of single and bi-layer cuprates using the gauge-field description of the t-J model. For $T>T_{\text{BE}}$ the in-plane fermion-pairing order parameter $\Delta_{\scriptscriptstyle\parallel}$ is eliminated by gauge field fluctuations, leading us to predict the absence of a spin-gap phase in single-layer cuprates. For bi-layer cuprates the inter-layer order parameter $\Delta_\perp$ is enhanced by spin correlations, and is less affected by gauge fluctuations. We believe that the spin gap in bi-layer materials is due to inter-layer fermion pairing, and that for these underdoped samples the superconducting gap may be nodeless.