14,589 research outputs found
Competition between hidden order and antiferromagnetism in URu_2Si_2 under uniaxial stress studied by neutron scattering
We have performed elastic neutron scattering experiments under uniaxial
stress sigma applied along the tetragonal [100], [110] and [001] directions for
the heavy electron compound URu2Si2. We found that antiferromagnetic (AF) order
with large moment is developed with sigma along the [100] and [110] directions.
If the order is assumed to be homogeneous, the staggered ordered moment mu_o
continuously increases from 0.02 mu_B (sigma=0) to 0.22 mu_B (0.25 GPa). The
rate of increase partial mu_o/partial sigma is ~ 1.0 mu_B/GPa, which is four
times larger than that for the hydrostatic pressure (partial mu_o/partial P sim
0.25 mu_B/GPa). Above 0.25 GPa, mu_o shows a tendency to saturate, similar to
the hydrostatic pressure behavior. For sigma||[001], mu_o shows only a slight
increase to 0.028 mu_B (sigma = 0.46 GPa) with a rate of ~ 0.02 mu_B/GPa,
indicating that the development of the AF state highly depends on the direction
of sigma. We have also found a clear hysteresis loop in the isothermal
mu_o(sigma) curve obtained for sigma||[110] under the zero-stress-cooled
condition at 1.4 K. This strongly suggests that the sigma-induced AF phase is
metastable, and separated from the "hidden order" phase by a first-order phase
transition. We discuss these experimental results on the basis of crystalline
strain effects and elastic energy calculations, and show that the c/a ratio
plays a key role in the competition between these two phases.Comment: 9 pages, 7 figures, to appear in Physical Review
Matter power spectrum in f(R) gravity with massive neutrinos
The effect of massive neutrinos on matter power spectrum is discussed in the
context of gravity. It is shown that the anomalous growth of density
fluctuations on small scales due to the scalaron force can be compensated by
free streaming of neutrinos. As a result, models which predict observable
deviation of the equation-of-state parameter w_\DE from w_\DE=-1 can be
reconciled with observations of matter clustering if the total neutrino mass is
O(0.5 \eV).Comment: 8 pages, 6 figures; Discussion expanded, references added, results
unchanged, matches the version to be published in PT
Controllable spin transport in ferromagnetic graphene junctions
We study spin transport in normal/ferromagnetic/normal graphene junctions
where a gate electrode is attached to the ferromagnetic graphene. We find that
due to the exchange field of the ferromagnetic graphene, spin current through
the junctions has an oscillatory behavior with respect to the chemical
potential in the ferromagnetic graphene, which can be tuned by the gate
voltage. Especially, we obtain a controllable spin current reversal by the gate
voltage. Our prediction of high controllability of spin transport in
ferromagnetic graphene junction may contribute to the development of the
spintronics.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev.
Cosmology Based on f(R) Gravity Admits 1 eV Sterile Neutrinos
It is shown that the tension between recent neutrino oscillation experiments,
favoring sterile neutrinos with masses of the order of 1 eV, and cosmological
data which impose stringent constraints on neutrino masses from the free
streaming suppression of density fluctuations, can be resolved in models of the
present accelerated expansion of the Universe based on f(R) gravity.Comment: 5 pages, 3 figures, matches the published version in Phys. Rev. Let
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