2,080 research outputs found
Duality Argument for the Chiral-Nematic Phase of Planar Spins
A duality argument for the recently discovered chiral-nematic phase of the XY
model in a triangular lattice is presented. We show that a new Ising variable
naturally emerges in mapping the antiferromagnetic J1-J2 classical XY spin
Hamiltonian onto an appropriate Villain model on a triangular lattice. The new
variable is the chirality degree of freedom, which exists in addition to the
usual vortex variables, in the dual picture. Elementary excitations and the
associated phase transition of the Ising degrees of freedom are discussed in
some detail.Comment: Published version(4 pages, 2 figures
Vector chiral states in low-dimensional quantum spin systems
A class of exact spin ground states with nonzero averages of vector spin
chirality, , is presented. It is
obtained by applying non-uniform O(2) rotations of spin operators in the XY
plane on the SU(2)-invariant Affleck-Kennedy-Lieb-Tasaki (AKLT) states and
their parent Hamiltonians. Excitation energies of the new ground states are
studied with the use of single-mode approximation in one dimension for S=1. The
excitation gap remains robust. Construction of chiral AKLT states is shown to
be possible in higher dimensions. We also present a general idea to produce
vector chirality-condensed ground states as non-uniform O(2) rotations of the
non-chiral parent states. Dzyaloshinskii-Moriya interaction is shown to imply
non-zero spin chirality.Comment: 4 pages, 1 figur
Coupling of phonons and spin waves in triangular antiferromagnet
We investigate the influence of the spin-phonon coupling in the triangular
antiferromagnet where the coupling is of the exchange-striction type. The
magnon dispersion is shown to be modified significantly at wave vector (2pi,0)
and its symmetry-related points, exhibiting a roton-like minimum and an
eventual instability in the dispersion. Various correlation functions such as
equal-time phonon correlation, spin-spin correlation, and local magnetization
are calculated in the presence of the coupling.Comment: 6 pages, 5 figures; references added, minor text revisions, submitted
to PR
Landau level states on a topological insulator thin film
We analyze the four-dimensional Hamiltonian proposed to describe the band
structure of the single-Dirac-cone family of topological insulators in the
presence of a uniform perpendicular magnetic field. Surface Landau level(LL)
states appear, decoupled from the bulk levels and following the quantized
energy dispersion of a purely two-dimensional surface Dirac Hamiltonian. A
small hybridization gap splits the degeneracy of the central n=0 LL with
dependence on the film thickness and the field strength that can be obtained
analytically. Explicit calculation of the spin and charge densities show that
surface LL states are localized within approximately one quintuple layer from
the surface termination. Some new surface-bound LLs are shown to exist at a
higher Landau level index.Comment: 8 pages, 4 figure
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