Hole on a stripe in a spinless fermion model

In the spinless fermion model on a square lattice with infinite nearest-neighbor repulsion, holes doped into the half-filled ordered state form stripes which, at low doping, are stable against phase separation into an ordered state and a hole-rich metal. Here we consider transport of additional holes along these stripes. The motion of a single hole on a stripe is mapped to a one-dimensional problem, a variational wavefunction is constructed and the energy spectrum is calculated and compared to energies obtained by exact diagonalization.Comment: 7 Pages, 6 figures; Revised version accepted for publication in Europhysics Letter

Semiclassical eigenstates of four-sublattice antiferromagnets

Applying Bohr-Sommerfeld quantization and the topological phase of spin path integrals, one can determine the multiplicities, lattice symmetries, and eigenvalue clustering pattern of the low-lying singlet eigenstates of the triangular and fcc antiferromagnets with 4-sublattice classical ground states. In the triangular case, the clustering pattern agrees with numerical results of Lecheminant et al (Phys. Rev. B 52, 6647 (1995)).Comment: 4 pages, 1 figure, 1 table. Clarifications, correction of inconsistent notations, and citation of Bernu et al 199

Effective Hamiltonians and dilution effects in kagome and related antiferromagnets

What is the zero-temperature ordering pattern of a Heisenberg antiferromagnet with large spin length $S$ (and possibly small dilution), on the kagome lattice, or others built from corner-sharing triangles and tetrahedra? First, I summarize the uses of effective Hamiltonians to resolve the large ground-state degeneracy, leading to long-range order of the usual kind. Secondly, I discuss the effects of dilution, in particular to {\it non}-frustration of classical ground states, in that every simplex of spins is optimally satisfied. Of three explanations for this, the most complete is Moessner-Chalker constraint-counting. Quantum zero-point energy may compete with classical exchange energy in a diluted system, creating frustration and enabling a spin-glass state. I suggest that the regime of over 97% occupation is qualitatively different from the more strongly diluted regime.Comment: 11 pages; invited talk at "HFM 2000" (Waterloo, June 2000); submitted to Can. J. Phy