Ordering in spatially anisotropic triangular antiferromagnets

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.Comment: 4 pages, 2 figures; v2: improved zero-field phase diagram, new figure

On the confinement of spinons in the CPM−1CP^{M-1} model

We use the $1/M$ expansion for the $CP^{M-1}$ model to study the long-distance behaviour of the staggered spin susceptibility in the commensurate, two-dimensional quantum antiferromagnet at finite temperature. At $M=\infty$ this model possesses deconfined spin-1/2 bosonic spinons (Schwinger bosons), and the susceptibility has a branch cut along the imaginary $k$ axis. We show that in all three scaling regimes at finite $T$, the interaction between spinons and gauge field fluctuations leads to divergent $1/M$ corrections near the branch cut. We identify the most divergent corrections to the susceptibility at each order in $1/M$ and explicitly show that the full static staggered susceptibility has a number of simple poles rather than a branch cut. We compare our results with the $1/N$ expansion for the $O(N)$ sigma-model.Comment: 27 pages, REVtex file, 4 figures (now in a uuencoded, gziped file). The figures are also available upon request

Equilibrium currents in chiral systems with non-zero Chern number

We describe simple quantum-mechanical approach to calculating equilibrium particle current along the edge of a system with non-trivial band spectrum topology. The approach does not require any a priori knowledge of the band topology and, as a matter of fact, treats topological and non-topological contributions to the edge currents on the same footing. We illustrate its usefulness by demonstrating the existence of `topologically non-trivial' particle currents along the edges of three different physical systems: two-dimensional electron gas with spin-orbit coupling and Zeeman magnetic field, surface state of a topological insulator, and kagome antiferromagnet with Dzyaloshinskii-Moriya interaction. We describe relation of our results to the notion of orbital magnetization.Comment: 8 pages, 4 figure