177 research outputs found
Magnetic anisotropy of the spin ice compound Dy2Ti2O7
We report magnetization and ac susceptibility of single crystals of the spin
ice compound Dy2Ti2O7. Saturated moments at 1.8 K along the charasteristic axes
[100] and [110] agree with the expected values for an effective ferromagnetic
nearest-neighbor Ising pyrochlore with local anisotropy, where each
magnetic moment is constrained to obey the `ice-rule'. At high enough magnetic
fields along the [111] axis, the saturated moment exhibits a beaking of the
ice-rule; it agrees with the value expected for a three-in one-out spin
configuration. Assuming the realistic magnetic interaction between Dy ions
given by the dipolar spin ice model, we completely reproduce the results at 2 K
by Monte Carlo calculations. However, down to at least 60 mK, we have not found
any experimental evidence of the long-range magnetic ordering predicted by this
model to occur at around 180 mK. Instead, we confirm the spin freezing of the
system below 0.5 K.Comment: 7 pages, 6 figures, submitted to Phys. Rev.
Persistent supersolid phase of hard-core bosons on the triangular lattice
We study hard-core bosons with unfrustrated hopping () and nearest
neighbour repulsion () on the triangular lattice. At half-filling, the
system undergoes a zero temperature () quantum phase transition from a
superfluid phase at small to a supersolid at in units of
. This supersolid phase breaks the lattice translation symmetry in a
characteristic pattern, and is remarkably
stable--indeed, a smooth extrapolation of our results indicates that the
supersolid phase persists for arbitrarily large .Comment: 4 pages, 5 figures, two column forma
Continuous thermal melting of a two-dimensional Abrikosov vortex solid
We examine the question of thermal melting of the triangular Abrikosov vortex
solid in two-dimensional superconductors or neutral superfluids. We introduce a
model, which combines lowest Landau level (LLL) projection with the magnetic
Wannier basis to represent degenerate eigenstates in the LLL. Solving the model
numerically via large-scale Monte Carlo simulations, we find clear evidence for
a continuous melting transition, in perfect agreement with the
Kosterlitz-Thouless-Halperin-Nelson-Young theory and with recent experiments.Comment: 4 pages, 2 figures; published versio
Classical Topological Order in Kagome Ice
We examine the onset of classical topological order in a nearest-neighbor
kagome ice model. Using Monte Carlo simulations, we characterize the
topological sectors of the groundstate using a non-local cut measure which
circumscribes the toroidal geometry of the simulation cell. We demonstrate that
simulations which employ global loop updates that are allowed to wind around
the periodic boundaries cause the topological sector to fluctuate, while
restricted local loop updates freeze the simulation into one topological
sector. The freezing into one topological sector can also be observed in the
susceptibility of the real magnetic spin vectors projected onto the kagome
plane. The ability of the susceptibility to distinguish between fluctuating and
non-fluctuating topological sectors should motivate its use as a local probe of
topological order in a variety of related model and experimental systems.Comment: 17 pages, 9 figure
Valence Bond Solids and Their Quantum Melting in Hard-Core Bosons on the Kagome Lattice
Using large scale quantum Monte Carlo simulations and dual vortex theory we
analyze the ground state phase diagram of hard-core bosons on the kagome
lattice with nearest neighbor repulsion. In contrast to the case of a
triangular lattice, no supersolid emerges for strong interactions. While a
uniform superfluid prevails at half-filling, two novel solid phases emerge at
densities and . These solids exhibit an only partial
ordering of the bosonic density, allowing for local resonances on a subset of
hexagons of the kagome lattice. We provide evidence for a weakly first-order
phase transition at the quantum melting point between these solid phases and
the superfluid.Comment: 4 pages, 7 figure
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