369 research outputs found
Possible role of 3He impurities in solid 4He
We use a quantum lattice gas model to describe essential aspects of the
motion of 4He atoms and of 3He impurities in solid 4He. This study suggests
that 3He impurities bind to defects and promote 4He atoms to interstitial sites
which can turn the bosonic quantum disordered crystal into a metastable
supersolid. It is suggested that defects and interstitial atoms are produced
during the solid 4He nucleation process where the role of 3He impurities (in
addition to the cooling rate) is known to be important even at very small (1
ppm) impurity concentration. It is also proposed that such defects can form a
glass phase during the 4He solid growth by rapid cooling.Comment: 4 two-column Revtex pages, 4 figures. Europhysics Letters (in Press
Giant Coulomb broadening and Raman lasing on ionic transitions
CW generation of anti-Stokes Raman laser on a number of blue-green argon-ion
lines (4p-4s, 4p-3d) has been demonstrated with optical pumping from metastable
levels 3d'^2G, 3d^4F. It is found, that the population transfer rate is
increased by a factor of 3-5 (and hence, the output power of such Raman laser)
owing to Coulomb diffusion in the velocity space. Measured are the excitation
and relaxation rates for the metastable level. The Bennett hole on the
metastable level has been recorded using the probe field technique. It has been
shown that the Coulomb diffusion changes shape of the contour to exponential
cusp profile while its width becomes 100 times the Lorentzian one and reaches
values close to the Doppler width. Such a giant broadening is also confirmed by
the shape of the absorption saturation curve.Comment: RevTex 18 pages, 5 figure
Thermal History of Solid 4He Under Oscillation
We have studied the thermal history of the resonant frequency of a torsional
oscillator containing solid 4He. We find that the magnitude of the frequency
shift that occurs below 100 mK is multivalued in the low temperature limit,
with the exact value depending on how the state is prepared. This result can be
qualitatively explained in terms of the motion and pinning of quantized
vortices within the sample. Several aspects of the data are also consistent
with the response of dislocation lines to oscillating stress fields imposed on
the solid.Comment: 7 pages, 6 figure
Dynamics of electrostatically-driven granular media. Effects of Humidity
We performed experimental studies of the effect of humidity on the dynamics
of electrostatically-driven granular materials. Both conducting and dielectric
particles undergo a phase transition from an immobile state (granular solid) to
a fluidized state (granular gas) with increasing applied field. Spontaneous
precipitation of solid clusters from the gas phase occurs as the external
driving is decreased. The clustering dynamics in conducting particles is
primarily controlled by screening of the electric field but is aided by
cohesion due to humidity. It is shown that humidity effects dominate the
clustering process with dielectric particles.Comment: 4 pages, 4 fig
High Throughput Petrochronology and Sedimentary Provenance Analysis by Automated Phase Mapping and LAICPMS
The first step in most geochronological studies is to extract dateable minerals from the host rock, which is time consuming, removes textural context, and increases the chance for sample cross contamination. We here present a new method to rapidly perform in situ analyses by coupling a fast scanning electron microscope (SEM) with Energy Dispersive X-ray Spectrometer (EDS) to a Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LAICPMS) instrument. Given a polished hand specimen, a petrographic thin section, or a grain mount, Automated Phase Mapping (APM) by SEM/EDS produces chemical and mineralogical maps from which the X-Y coordinates of the datable minerals are extracted. These coordinates are subsequently passed on to the laser ablation system for isotopic analysis. We apply the APM1LAICPMS method to three igneous, metamorphic, and sedimentary case studies. In the first case study, a polished slab of granite from Guernsey was scanned for zircon, producing a 60968 Ma weighted mean age. The second case study investigates a paragneiss from an ultra high pressure terrane in the north Qaidam terrane (Qinghai, China). One hundred seven small (25 mm) metamorphic zircons were analyzed by LAICPMS to confirm a 41964 Ma age of peak metamorphism. The third and final case study uses APM1LAICPMS to generate a large provenance data set and trace the provenance of 25 modern sediments from Angola, documenting longshore drift of Orange River sediments over a distance of 1,500 km. These examples demonstrate that APM1LAICPMS is an efficient and cost effective way to improve the quantity and quality of geochronological data
The genetics of the Lp Antigen
Several genetic models were considered to explain the distribution of qualitatively positive and negative children in 204 Caucasian families. A model which best describes the inheritance of the Lp antigenic expression involves a major genetic locus which distinguishes two overlapping continuously distributed modes of quantitative activity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66139/1/j.1469-1809.1974.tb01992.x.pd
Two-body correlations and the superfluid fraction for nonuniform systems
We extend the one-body phase function upper bound on the superfluid fraction
in a periodic solid (a spatially ordered supersolid) to include two-body phase
correlations. The one-body current density is no longer proportional to the
gradient of the one-body phase times the one-body density, but rather it
depends also on two-body correlation functions. The equations that
simultaneously determine the one-body and two-body phase functions require a
knowledge of one-, two-, and three-body correlation functions. The approach can
also be extended to disordered solids. Fluids, with two-body densities and
two-body phase functions that are translationally invariant, cannot take
advantage of this additional degree of freedom to lower their energy.Comment: 13 page
Ground states and dynamics of population-imbalanced Fermi condensates in one dimension
By using the numerically exact density-matrix renormalization group (DMRG)
approach, we investigate the ground states of harmonically trapped
one-dimensional (1D) fermions with population imbalance and find that the
Larkin-Ovchinnikov (LO) state, which is a condensed state of fermion pairs with
nonzero center-of-mass momentum, is realized for a wide range of parameters.
The phase diagram comprising the two phases of i) an LO state at the trap
center and a balanced condensate at the periphery and ii) an LO state at the
trap center and a pure majority component at the periphery, is obtained. The
reduced two-body density matrix indicates that most of the minority atoms
contribute to the LO-type quasi-condensate. With the time-dependent DMRG, we
also investigate the real-time dynamics of a system of 1D fermions in response
to a spin-flip excitation.Comment: 20 pages, 15 figures, accepted for publication in New Journal of
Physic
Solid 4He and the Supersolid Phase: from Theoretical Speculation to the Discovery of a New State of Matter? A Review of the Past and Present Status of Research
The possibility of a supersolid state of matter, i.e., a crystalline solid
exhibiting superfluid properties, first appeared in theoretical studies about
forty years ago. After a long period of little interest due to the lack of
experimental evidence, it has attracted strong experimental and theoretical
attention in the last few years since Kim and Chan (Penn State, USA) reported
evidence for nonclassical rotational inertia effects, a typical signature of
superfluidity, in samples of solid 4He. Since this "first observation", other
experimental groups have observed such effects in the response to the rotation
of samples of crystalline helium, and it has become clear that the response of
the solid is extremely sensitive to growth conditions, annealing processes, and
3He impurities. A peak in the specific heat in the same range of temperatures
has been reported as well as anomalies in the elastic behaviour of solid 4He
with a strong resemblance to the phenomena revealed by torsional oscillator
experiments. Very recently, the observation of unusual mass transport in hcp
solid 4He has also been reported, suggesting superflow. From the theoretical
point of view, powerful simulation methods have been used to study solid 4He,
but the interpretation of the data is still rather difficult; dealing with the
question of supersolidity means that one has to face not only the problem of
the coexistence of quantum coherence phenomena and crystalline order, exploring
the realm of spontaneous symmetry breaking and quantum field theory, but also
the problem of the role of disorder, i.e., how defects, such as vacancies,
impurities, dislocations, and grain boundaries, participate in the phase
transition mechanism.Comment: Published on J. Phys. Soc. Jpn., Vol.77, No.11, p.11101
Ultra-cold Polarized Fermi Gases
Recent experiments with ultra-cold atoms have demonstrated the possibility of
realizing experimentally fermionic superfluids with imbalanced spin
populations. We discuss how these developments have shed a new light on a half-
century old open problem in condensed matter physics, and raised new
interrogations of their own.Comment: 27 pages; 8 figures; Published in Report in Rep. Prog. Phys. 73
112401 (2010
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