2,121 research outputs found
Resonating color state and emergent chromodynamics in the kagome antiferromagnet
We argue that the spin-wave breakdown in the Heisenberg kagome
antiferromagnet signals an instability of the ground state and leads, through
an emergent local constraint, to a quantum dynamics described by a gauge theory
similar to that of chromodynamics. For integer spins, we show that the quantum
fluctuations of the gauge modes select the sqrt(3)xsqrt(3) Neel state with an
on-site moment renormalized by color resonances. We find non-magnetic
low-energy excitations that may be responsible for a deconfinement "transition"
at experimentally accessible temperatures which we estimate.Comment: 4 pages, 4 figures, v2: printable figs, v3: publ. versio
Ill-Behaved Convergence of a Model of the Gd3Ga5O12 Garnet Antiferromagnet with Truncated Magnetic Dipole-Dipole Interactions
Previous studies have found that calculations which consider long-range
magnetic dipolar interactions truncated at a finite cut-off distance Rc predict
spurious (unphysical) long-range ordered phases for Ising and Heisenberg
systems on the pyrochlore lattice. In this paper we show that, similar to these
two cases, calculations that use truncated dipolar interactions to model the
Gd3Ga5O12 garnet antiferromagnet also predict unphysical phases with
incommensurate ordering wave vector q_ord that is very sensitive to the dipolar
cut-off distance Rc.Comment: 7 pages, 2 color figures; Proceedings of the HFM2006 conference, to
appear in a special issue of J. Phys.: Condens. Matte
Momentum dependent light scattering in insulating cuprates
We investigate the problem of inelastic x-ray scattering in the spin
Heisenberg model on the square lattice. We first derive a momentum dependent
scattering operator for the and polarization geometries. On
the basis of a spin-wave analysis, including magnon-magnon interactions and
exact-diagonalizations, we determine the qualitative shape of the spectra. We
argue that our results may be relevant to help interpret inelastic x-ray
scattering experiments in the antiferromagnetic phase of the cuprates.Comment: 5 pages, 3 figures, to appear in PR
Frustrated Quantum Rare-Earth Pyrochlores
In this review, we provide an introduction to the physics of a series of frustrated quantum rare-earth pyrochlores. We first give a background on the microscopic single-and two-ion physics of these materials, discussing the origins and properties of their exchange interactions and their minimal lowenergy effective models before outlining what is known about their classical and quantum phases. We then make use of this understanding to discuss four important material examples, Er2Ti2O7, Yb2Ti2O7, Tb2Ti2O7, and Pr2Zr2O7, covering in some detail what is known experimentally and theoretically for each and then summarizing some key questions that remain open. Finally, we offer an outlook on some alternative material platforms for realizing similar physics and discuss what we see as prospects for future investigations on these quantum rare-earth pyrochlores
Is the Yb2Ti2O7 pyrochlore a quantum spin ice?
We use numerical linked cluster (NLC) expansions to compute the specific
heat, C(T), and entropy, S(T), of a quantum spin ice model of Yb2Ti2O7 using
anisotropic exchange interactions recently determined from inelastic neutron
scattering measurements and find good agreement with experimental calorimetric
data. In the perturbative weak quantum regime, this model has a ferrimagnetic
ordered ground state, with two peaks in C(T): a Schottky anomaly signalling the
paramagnetic to spin ice crossover followed at lower temperature by a sharp
peak accompanying a first order phase transition to the ferrimagnetic state. We
suggest that the two C(T) features observed in Yb2Ti2O7 are associated with the
same physics. Spin excitations in this regime consist of weakly confined
spinon-antispinon pairs. We suggest that conventional ground state with exotic
quantum dynamics will prove a prevalent characteristic of many real quantum
spin ice materials.Comment: 8 pages (two-column), 9 figure
Magnetic charge and ordering in kagome spin ice
We present a numerical study of magnetic ordering in spin ice on kagome, a
two-dimensional lattice of corner-sharing triangles. The magnet has six ground
states and the ordering occurs in two stages, as one might expect for a
six-state clock model. In spin ice with short-range interactions up to second
neighbors, there is an intermediate critical phase separated from the
paramagnetic and ordered phases by Kosterlitz-Thouless transitions. In dipolar
spin ice, the intermediate phase has long-range order of staggered magnetic
charges. The high and low-temperature phase transitions are of the Ising and
3-state Potts universality classes, respectively. Freeze-out of defects in the
charge order produces a very large spin correlation length in the intermediate
phase. As a result of that, the lower-temperature transition appears to be of
the Kosterlitz-Thouless type.Comment: 20 pages, 12 figures, accepted version with minor change
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.
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