180 research outputs found
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
Corner contribution to the entanglement entropy of strongly-interacting O(2) quantum critical systems in 2+1 dimensions
In a D=2+1 quantum critical system, the entanglement entropy across a
boundary with a corner contains a subleading logarithmic scaling term with a
universal coefficient. It has been conjectured that this coefficient is, to
leading order, proportional to the number of field components N in the
associated O(N) continuum field theory. Using density matrix
renormalization group calculations combined with the powerful numerical linked
cluster expansion technique, we confirm this scenario for the O(2)
Wilson-Fisher fixed point in a striking way, through direct calculation at the
quantum critical points of two very different microscopic models. The value of
this corner coefficient is, to within our numerical precision, twice the
coefficient of the Ising fixed point. Our results add to the growing body of
evidence that this universal term in the R\'enyi entanglement entropy reflects
the number of low-energy degrees of freedom in a system, even for strongly
interacting theories.Comment: 6 pages, 6 figure
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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