Large N expansion for frustrated and doped quantum antiferromagnets

TL;DR

This paper develops a large N expansion method using symplectic symmetry to analyze frustrated quantum antiferromagnets, revealing diverse disordered phases and their properties, with implications for understanding quantum magnetism and superconductivity.

Contribution

It introduces a novel large N expansion technique based on Sp(N) symmetry for frustrated magnetic systems and explores the phase diagram of the J_1-J_2-J_3 model.

Findings

Identification of two classes of disordered phases with distinct spin correlations.

Demonstration of the role of fluctuations at finite N in phase stability.

Initial results suggesting possible superconductivity in the t-J model at N=infinity.

Abstract

A large N expansion technique, based on symplectic (Sp(N)) symmetry, for frustrated magnetic systems is studied. The phase diagram of a square lattice, spin S, quantum antiferromagnet with first, second and third neighbor antiferromagnetic coupling (the J_1-J_2-J_3 model) is determined in the large-N limit and consequences of fluctuations at finite N for the quantum disordered phases are discussed. In addition to phases with long range magnetic order, two classes of disordered phases are found: (i) states similar to those in unfrustrated systems with commensurate, collinear spin correlations, confinement of spinons, and spin-Peierls or valence-bond-solid order controlled by the value of 2S(mod 4) or 2S(mod 2); (ii) states with incommensurate, coplanar spin correlations, and unconfined bosonic spin-1/2 spinon excitations. The occurrence of ``order from disorder'' at large S is discussed. Neither chirally ordered nor spin nematic states are found. Initial results on superconductivity in the t-J model at N=infinity and zero temperature are also presented.