Spin-gap formation in cuprates: gauge theory

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 ${\Delta }_{\parallel }$ 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.

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