Monopole Flux State on the Pyrochlore Lattice

TL;DR

This paper investigates the ground state of a quantum Heisenberg antiferromagnet on the pyrochlore lattice, revealing a novel monopole flux state with a unique Fermi surface and gapless excitations, stable against small fluctuations.

Contribution

It introduces a new monopole flux state with a chiral phase and a distinctive Fermi surface, analyzed using large N mean field theory and symmetry considerations.

Findings

Identifies a monopole flux state breaking parity and time reversal symmetry.

Finds a Fermi surface with four intersecting lines.

States the low-energy excitations are gapless spinons.

Abstract

The ground state of a spin 1/2 nearest neighbor quantum Heisenberg antiferromagnet on the pyrochlore lattice is investigated using a large $N$ SU(N) fermionic mean field theory. We find several mean field states, of which the state of lowest energy upon Gutzwiller projection, is a parity and time reversal breaking chiral phase with a unit monopole flux exiting each tetrahedron. This "monopole flux" state has a Fermi surface consisting of 4 lines intersecting at a point. At mean field the low-energy excitations about the Fermi surface are gapless spinons. An analysis using the projective symmetry group of this state suggests that the state is stable to small fluctuations which neither induce a gap, nor alter the unusual Fermi surface.