529 research outputs found
Dissipative superfluid mass flux through solid 4He
The thermo-mechanical effect in superfluid helium is used to create an
initial chemical potential difference, , across a solid He
sample. This causes a flow of helium atoms from one reservoir
filled with superfluid helium, through a sample cell filled with solid helium,
to another superfluid-filled reservoir until chemical potential equilibrium is
restored. The solid helium sample is separated from each of the reservoirs by
Vycor rods that allow only the superfluid component to flow. With an improved
technique, measurements of the flow, , at several fixed solid helium
temperatures, , have been made as function of in the pressure
range 25.5 - 26.1 bar. And, measurements of have been made as a function of
temperature in the range ~mK for several fixed values of . The temperature dependence of the flow above ~mK shows a reduction
of the flux with an increase in temperature that is well described by . The non-linear functional dependence , with independent of temperature but dependent on pressure,
documents in some detail the dissipative nature of the flow and suggests that
this system demonstrates Luttinger liquid-like one-dimensional behavior. The
mechanism that causes this flow behavior is not certain, but is consistent with
superflow on the cores of edge dislocations.Comment: 11 pages, 14 figure
Mass flux characteristics in solid 4He for T> 100 mK: Evidence for Bosonic Luttinger Liquid behavior
At pressure 25.7 bar the flux, , carried by solid \4he for
100 mK depends on the net chemical potential difference between two reservoirs
in series with the solid, , and obeys ,
where is independent of temperature. At fixed the
temperature dependence of the flux, , can be adequately represented by , K, for K. A
single function fits all of the available
data sets in the range 25.6 - 25.8 bar reasonably well. We suggest that the
mass flux in solid \4he for mK may have a Luttinger liquid-like
behavior in this bosonic system.Comment: 4 pages, 5 figure
Observation of thermo-mechanical equilibration in the presence of a solid 4He conduit
We observe a thermo-mechanical effect when a chemical potential difference is
created by a temperature difference imposed between two liquid reservoirs
connected to each other through Vycor rods in series with solid hcp 4He. By
creating a temperature difference, , between the two reservoirs, we
induce a rate-limited growth of a pressure difference between the two
reservoirs, . In equilibrium is in
quantitative agreement with the thermo-mechanical effect in superfluid helium.
These observations confirm that below 600 mK a flux-limited flow exists
through the solid helium.Comment: 4 pages, 4 figure
Growth of solid hcp \^4He off the melting curve
We report studies of the growth of solid hcp \4he at pressures higher than
the bulk freezing pressure using a cell design that allows us to inject atoms
into the solid. Near the melting curve during injection we observe random
events during which the pressure recorded in the cell drops abruptly. These
events are accompanied by transient increases in the temperature of the cell.
We discuss these transients and conclude that they represent the solidification
of meta-stable liquid regions and the associated relief of strain in the local
solid. We also observe that further from the melting curve the transients are
no longer recorded, but that we can continue to add atoms to the solid,
increasing its density at fixed volume. We document these changes in density
with respect to changes in the chemical potential as a function of temperature
and discuss these in the context of recent theoretical work.Comment: 7 pages, 8 figure
Mass flow through solid 4He induced by the fountain effect
Using an apparatus that allows superfluid liquid 4He to be in contact with
hcp solid \4he at pressures greater than the bulk melting pressure of the
solid, we have performed experiments that show evidence for 4He mass flux
through the solid and the likely presence of superfluid inside the solid. We
present results that show that a thermomechanical equilibrium in quantitative
agreement with the fountain effect exists between two liquid reservoirs
connected to each other through two superfluid-filled Vycor rods in series with
a chamber filled with solid 4He. We use the thermomechanical effect to induce
flow through the solid and measure the flow rate. On cooling, mass flux appears
near T = 600 mK and rises smoothly as the temperature is lowered. Near T = 75
mK a sharp drop in the flux is present. The flux increases as the temperature
is reduced below 75 mK. We comment on possible causes of this flux minimum.Comment: 20 pages, 22 figures, 7 table
Observation of Mass Transport through Solid 4He
By use of a novel experimental design, one that provides for superfluid
helium in contact with bulk hcp 4He off the melting curve, we have observed the
DC transport of mass through a cell filled with solid 4He in the hcp region of
the phase diagram. Flow, which shows characteristics of a superflow, is seen to
be independent of the method used to grow the solid, but depends on pressure
and temperature. The temperature dependence suggests the possibility of
hysteresis.Comment: 1 zipped file, produces 16 page paper, with 20 figures; resubmitted
with typos corrected, a figure corrected, some discussion improved, and
additional references - still 16 pages and 20 figure
Quantum Monte Carlo Algorithm Based on Two-Body Density Functional Theory for Fermionic Many-Body Systems: Application to 3He
We construct a quantum Monte Carlo algorithm for interacting fermions using
the two-body density as the fundamental quantity. The central idea is mapping
the interacting fermionic system onto an auxiliary system of interacting
bosons. The correction term is approximated using correlated wave functions for
the interacting system, resulting in an effective potential that represents the
nodal surface. We calculate the properties of 3He and find good agreement with
experiment and with other theoretical work. In particular, our results for the
total energy agree well with other calculations where the same approximations
were implemented but the standard quantum Monte Carlo algorithm was usedComment: 4 pages, 3 figures, 1 tabl
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