Properties of an algebraic spin liquid on the kagome lattice
  In recent work, we argued that a particular algebraic spin liquid (ASL) may be the ground state of the S = 1/2 kagome lattice Heisenberg antiferromagnet. This state, which lacks a spin gap, is appealing in light of recent experiments on herbertsmithite (ZnCu3(OH)6Cl2). Here, we study the properties of this ASL in more detail, using both the low-energy effective field theory and Gutzwiller-projected wavefunctions. We identify the competing orders of the ASL -- among them we find a set of magnetic orders lying at the M-points of the Brillouin zone, the q = 0 magnetic ordered state, the "Hastings" valence-bond solid (VBS) state, and a pattern of vector spin chirality ordering corresponding to one of the Dzyaloshinskii-Moriya (DM) interaction terms present in herbertsmithite. We discuss the detection of the magnetic and VBS competing orders in experiments. While we focus on a clean system without DM interaction, we consider the effects of small DM interaction and argue that, surprisingly, it leads to spontaneously broken time reversal symmetry (for DM interaction that preserves XY spin rotation symmetry, there is also XY magnetic order). Our analysis of the projected wavefunction provides an estimate of the "Fermi velocity" that characterizes all low-energy excitations of the ASL -- this allows us to estimate the specific heat, which compares favorably with experiments. We also study the spin and bond correlations of the projected wavefunction and compare these results with those of the effective field theory. While the spin correlations in the effective field theory and wavefunction seem to match rather well (although not completely), the bond correlations are more puzzling. We conclude with a discussion of experiments in herbertsmithite and make several predictions. 
Michael Hermele, Ying Ran, Patrick A. Lee and Xiao-Gang Wen