2,487 research outputs found
Light majoron cold dark matter from topological defects and the formation of boson stars
We show that for a relatively light majoron ( eV) non-thermal
production from topological defects is an efficient production mechanism.
Taking the type I seesaw as benchmark scheme, we estimate the primordial
majoron abundance and determine the required parameter choices where it can
account for the observed cosmological dark matter. The latter is consistent
with the scale of unification. Possible direct detection of light majorons with
future experiments such as PTOLEMY and the formation of boson stars from the
majoron dark matter are also discussed.Comment: 27 pages, 3 figures; v2: references added, matches published versio
Collision of one-dimensional fermion clusters
We study cluster-cluster collisions in one-dimensional Fermi systems with
particular emphasis on the non-trivial quantum effects of the collision
dynamics. We adopt the Fermi-Hubbard model and the time-dependent density
matrix renormalization group method to simulate collision dynamics between two
fermion clusters of different spin states with contact interaction. It is
elucidated that the quantum effects become extremely strong with the
interaction strength, leading to the transmittance much more enhanced than
expected from semiclassical approximation. We propose a concise model based on
one-to-one collisions, which unveils the origin of the quantum effects and also
explains the overall properties of the simulation results clearly. Our concise
model can quite widely describe the one-dimensional collision dynamics with
contact interaction. Some potential applications, such as repeated collisions,
are addressed.Comment: 5 pages, 5 figure
Universal temperature dependence of the magnetization of gapped spin chains
Temperature dependence of the magnetization of the Haldane spin chain at
finite magnetic field is analyzed systematically. Quantum Monte Carlo data
indicates a clear minimum of magnetization as a function of temperature in the
gapless regime. On the basis of the Tomonaga-Luttinger liquid theory, we argue
that this minimum is rather universal and can be observed for general axially
symmetric quasi-one-dimensional spin systems. Our argument is confirmed by the
magnetic-field dependence of the spin-wave velocity obtained numerically. One
can estimate a magnitude of the gap of any such systems by fitting the
experimental data with the magnetization minimum.Comment: 9 pages, 7 figure
Experimental Test of a New Equality: Measuring Heat Dissipation in an Optically Driven Colloidal System
Measurement of energy dissipation in small nonequilibrium systems is
generally a difficult task. Recently, Harada and Sasa [Phys.Rev.Lett. 95,
130602(2005)] derived an equality relating the energy dissipation rate to
experimentally accessible quantities in nonequilibrium steady states described
by the Langevin equation. Here, we show the first experimental test of this new
relation in an optically driven colloidal system. We find that this equality is
validated to a fairly good extent, thus the irreversible work of a small system
is estimated from readily obtainable quantities.Comment: 4 pages, 6 figure
Single-ion anisotropy in Haldane chains and form factor of the O(3) nonlinear sigma model
We consider spin-1 Haldane chains with single-ion anisotropy, which exists in
known Haldane chain materials. We develop a perturbation theory in terms of
anisotropy, where magnon-magnon interaction is important even in the low
temperature limit. The exact two-particle form factor in the O(3) nonlinear
sigma model leads to quantitative predictions on several dynamical properties
including dynamical structure factor and electron spin resonance frequency
shift. These agree very well with numerical results, and with experimental data
on the Haldane chain material Ni(CHN)N(PF)
Single-Crystal Organic Charge-Transfer Interfaces probed using Schottky-Gated Heterostructures
Organic semiconductors based on small conjugated molecules generally behave
as insulators when undoped, but the hetero-interfaces of two such materials can
show electrical conductivity as large as in a metal. Although charge transfer
is commonly invoked to explain the phenomenon, the details of the process and
the nature of the interfacial charge carriers remain largely unexplored. Here
we use Schottky-gated heterostructures to probe the conducting layer at the
interface between rubrene and PDIF-CN2 single crystals. Gate-modulated
conductivity measurements demonstrate that interfacial transport is due to
electrons, whose mobility exhibits band-like behavior from room temperature to
~ 150 K, and remains as high as ~ 1 cm2V-1s-1 at 30 K for the best devices. The
electron density decreases linearly with decreasing temperature, an observation
that can be explained quantitatively based on the heterostructure band diagram.
These results elucidate the electronic structure of rubrene-PDIF-CN2 interfaces
and show the potential of Schottky-gated organic heterostructures for the
investigation of transport in molecular semiconductors.Comment: 37 pages, 9 Figures (including supplementary information
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