Classical antiferromagnet on a hyperkagome lattice

TL;DR

This paper investigates the classical antiferromagnet on a hyperkagome lattice, revealing highly degenerate ground states and emergent nematic order at low temperatures through theoretical and computational methods.

Contribution

It introduces the hyperkagome lattice as a new frustrated system and analyzes its classical spin behavior using large-N mean field theory and Monte Carlo simulations.

Findings

Highly degenerate classical ground states

Emergence of nematic order via order by disorder

Implications for experimental observations

Abstract

Motivated by recent experiments on Na_4Ir_3O_8 [Y. Okamoto, M. Nohara, H. Aruga-Katori, and H. Takagi, arXiv:0705.2821 (unpublished)], we study the classical antiferromagnet on a frustrated three-dimensional lattice obtained by selectively removing one of four sites in each tetrahedron of the pyrochlore lattice. This ``hyperkagome'' lattice consists of corner-sharing triangles. We present the results of large-N mean field theory and Monte Carlo computations on O(N) classical spin models. It is found that the classical ground states are highly degenerate. Nonetheless a nematic order emerges at low temperatures in the Heisenberg model (N=3) via ``order by disorder'', representing the dominance of coplanar spin configurations. Implications for ongoing experiments are discussed.