Inhomogeneous states and nodal fermions in the SU(2) gauge theory

TL;DR

This paper explores phase separation and nodal fermions in the SU(2) gauge theory of doped Mott insulators, revealing how holon interactions and isospin spirals explain coexistence of superconductivity and insulating states.

Contribution

It introduces the concept of an isospin spiral based on projective symmetry, explaining coexistence of superconductivity and Mott insulators, and demonstrates the significance of holon interactions in the SU(2) slave boson framework.

Findings

Holons behave as hard-core particles, even in the empty limit.

Phase separation and a d+s order parameter structure are observed in the overdoped regime.

Nodal fermions can persist despite charge inhomogeneities.

Abstract

We discuss the issue of phase separation in the SU(2) slave boson theory of Wen and Lee of the doped Mott insulator. It is shown that the constraint structure of the theory leads to the interpretation of the holons to have hard-core interactions, which is demonstrated further by studying the empty limit (no electrons). Surprisingly, with hard-core interactions even the empty limit is described well by the slave-boson theory, both as an energy density and with the regard to dynamical properties. The consequences are investigated in the overdoped superconducting regime, where both phase separation and a d+s structure of the order parameter is obtained. This s-wave component is already imminent in the description of the hole in the slave boson theory. The interacting nature of the holons also lead to sound modes in the single-electron propagator. The novel idea of the isospin spiral is introduced, based on the projective symmetry principles of Wen. This isospin spiral explains the coexistence of superconductivity and the Mott insulating state, being the consequence of phase separation. Secondly, it might be able to explain why nodal fermions survive in the presence of charge inhomogeneities.