Excitation spectrum of the homogeneous spin liquid

TL;DR

This paper investigates the excitation spectrum of a 2D Heisenberg antiferromagnet's spin liquid state, revealing that excitations are spin-1 dimers modeled by bond Bosons, providing insights into antiferromagnetic order and high-temperature superconductivity.

Contribution

It introduces a bond Boson model for excitations in the spin liquid state, differing from fermionic spinon descriptions, and links dimer condensation to antiferromagnetic order.

Findings

Excitations are spin-1 dimers, not spinons.

Bond Boson Hamiltonian analogous to spin wave theory.

Dimer condensation relates to antiferromagnetic order.

Abstract

We discuss the excitation spectrum of a disordered, isotropic and translationally invariant spin state in the 2D Heisenberg antiferromagnet. The starting point is the nearest-neighbor RVB state which plays the role of the vacuum of the theory, in a similar sense as the Neel state is the vacuum for antiferromagnetic spin wave theory. We discuss the elementary excitations of this state and show that these are not Fermionic spin-1/2 `spinons' but spin-1 excited dimers which must be modeled by bond Bosons. We derive an effective Hamiltonian describing the excited dimers which is formally analogous to spin wave theory. Condensation of the bond-Bosons at zero temperature into the state with momentum (pi,pi) is shown to be equivalent to antiferromagnetic ordering. The latter is a key ingredient for a microscopic interpretation of Zhang's SO(5) theory of cuprate superconductivity