title: Weak ferromagnetic exchange and anomalous specific heat in ZnCu3(OH)6Cl2.
abstract: Experimental evidence for a plethora of low energy spin excitations in the spin-1/2 kagome antiferromagnet ZnCu3(OH)6Cl2 may be understandable in terms of an extended Fermi surface of spinons coupled to a U(1) gauge field. We carry out variational calculations to examine the possibility that such a state may be energetically viable. A Gutzwiller-projected wave function reproduces the dimerization of a kagome strip found previously by the density matrix renormalization group. Application to the full kagome lattice shows that the inclusion of a small ferromagnetic next-nearest-neighbor interaction favors a ground state with a spinon Fermi surface.
authors.affiliation: Department of Physics, Brown University, Providence, Rhode Island 02912-1843, USA. Seungwook_Ma@brown.edu
authors.forename: Ookie
authors.initials: O
authors.lastname: Ma
authors.forename: J B
authors.initials: JB
authors.lastname: Marston