Ordering in spatially anisotropic triangular antiferromagnets

TL;DR

This paper explores the phase diagram of anisotropic triangular antiferromagnets, revealing competition between different magnetic orders and identifying quantum phase transitions influenced by fluctuations.

Contribution

It provides new insights into the phase transitions and magnetic orders in anisotropic triangular antiferromagnets, especially in the context of Cs_2CuCl_4.

Findings

Fluctuations induce competition between collinear antiferromagnetic and dimer orders.

Quantum phase transitions separate these from spiral order.

Magnetic field induces a sequence of ordered phases before full polarization.

Abstract

We investigate the phase diagram of the anisotropic spin-1/2 triangular lattice antiferromagnet, with interchain diagonal exchange J' much weaker than the intrachain exchange J. We find that fluctuations lead to a competition between (commensurate) collinear antiferromagnetic and (zig-zag) dimer orders. Both states differ in symmetry from the spiral order known to occur for larger J', and are therefore separated by quantum phase transitions from it. The zero-field collinear antiferromagnet is succeeded in a magnetic field by magnetically-ordered spin-density-wave and cone phases, before reaching the fully polarized state. Implications for the anisotropic triangular magnet Cs_2CuCl_4 are discussed.