Variational studies of triangular Heisenberg antiferromagnet in magnetic field

Abstract

We present a variational study of the Heisenberg antiferromagnet on the spatially anisotropic triangular lattice in magnetic field. First we construct a simple yet accurate wave function for the 1/3-magnetization plateau uud phase on the isotropic lattice. Beginning with this state, we obtain natural extensions to nearby commensurate coplanar phases on either side of the plateau. The latter occur also for low lattice anisotropy while the uud state extends to much larger anisotropy. Far away from the 1/3 plateau and for significant anisotropy, incommensurate states have better energetics, and we address competition between coplanar and noncoplanar states in the high-field regime. For very strong anisotropy, our study is dominated by quasi-one-dimensional physics. The variational study is supplemented by exact diagonalization calculations which provide a reference for testing the energetics of our trial wave functions as well as helping to identify candidate phases.