Symmetry Breaking on the Three-Dimensional Hyperkagome Lattice of Na_4Ir_3O_8

TL;DR

This paper investigates the frustrated hyperkagome lattice of Na_4Ir_3O_8, proposing a valence bond crystal ground state with low-energy excitations and discussing finite temperature signatures of symmetry breaking.

Contribution

It introduces a novel valence bond crystal ground state for the hyperkagome lattice and analyzes its excitations and finite temperature behavior.

Findings

Proposes a 72-site valence bond crystal ground state.

Identifies low-lying singlet excitations and confined spinons and triplons.

Predicts finite temperature signatures including an Ising transition.

Abstract

We study the antiferromagnetic spin-1/2 Heisenberg model on the highly frustrated, three-dimensional, hyperkagome lattice of Na_4Ir_3O_8 using a series expansion method. We propose a valence bond crystal with a 72 site unit cell as a ground state that supports many, very low lying, singlet excitations. Low energy spinons and triplons are confined to emergent lower-dimensional motifs. Here, and for analogous kagome and pyrochlore states, we suggest finite temperature signatures, including an Ising transition, in the magnetic specific heat due to a multistep breaking of discrete symmetries.