19 research outputs found
On the Temperature Dependence of the Casimir Effect
The temperature dependence of the Casimir force between a real metallic plate
and a metallic sphere is analyzed on the basis of optical data concerning the
dispersion relation of metals such as gold and copper. Realistic permittivities
imply, together with basic thermodynamic considerations, that the transverse
electric zero mode does not contribute. This results in observable differences
with the conventional prediction, which does not take this physical requirement
into account. The results are shown to be consistent with the third law of
thermodynamics, as well as being consistent with current experiments. However,
the predicted temperature dependence should be detectable in future
experiments. The inadequacies of approaches based on {\it ad hoc} assumptions,
such as the plasma dispersion relation and the use of surface impedance without
transverse momentum dependence, are discussed.Comment: 14 pages, 3 eps figures, revtex4. New version includes clarifications
and new reference. Accepted for publication in Phys. Rev.
What is the Temperature Dependence of the Casimir Effect?
There has been recent criticism of our approach to the Casimir force between
real metallic surfaces at finite temperature, saying it is in conflict with the
third law of thermodynamics and in contradiction with experiment. We show that
these claims are unwarranted, and that our approach has strong theoretical
support, while the experimental situation is still unclear.Comment: 6 pages, REVTeX, final revision includes two new references and
related discussio
The Casimir Problem of Spherical Dielectrics: Quantum Statistical and Field Theoretical Approaches
The Casimir free energy for a system of two dielectric concentric nonmagnetic
spherical bodies is calculated with use of a quantum statistical mechanical
method, at arbitrary temperature. By means of this rather novel method, which
turns out to be quite powerful (we have shown this to be true in other
situations also), we consider first an explicit evaluation of the free energy
for the static case, corresponding to zero Matsubara frequency ().
Thereafter, the time-dependent case is examined. For comparison we consider the
calculation of the free energy with use of the more commonly known field
theoretical method, assuming for simplicity metallic boundary surfaces.Comment: 31 pages, LaTeX, one new reference; version to appear in Phys. Rev.
Analytical and Numerical Demonstration of How the Drude Dispersive Model Satisfies Nernst's Theorem for the Casimir Entropy
In view of the current discussion on the subject, an effort is made to show
very accurately both analytically and numerically how the Drude dispersive
model, assuming the relaxation is nonzero at zero temperature (which is the
case when impurities are present), gives consistent results for the Casimir
free energy at low temperatures. Specifically, we find that the free energy
consists essentially of two terms, one leading term proportional to T^2, and a
next term proportional to T^{5/2}. Both these terms give rise to zero Casimir
entropy as T -> 0, thus in accordance with Nernst's theorem.Comment: 11 pages, 4 figures; minor changes in the discussion. Contribution to
the QFEXT07 proceedings; matches version to be published in J. Phys.
The Casimir Problem of Spherical Dielectrics: Numerical Evaluation for General Permittivities
The Casimir mutual free energy F for a system of two dielectric concentric
nonmagnetic spherical bodies is calculated, at arbitrary temperatures. The
present paper is a continuation of an earlier investigation [Phys. Rev. E {\bf
63}, 051101 (2001)], in which F was evaluated in full only for the case of
ideal metals (refractive index n=infinity). Here, analogous results are
presented for dielectrics, for some chosen values of n. Our basic calculational
method stems from quantum statistical mechanics. The Debye expansions for the
Riccati-Bessel functions when carried out to a high order are found to be very
useful in practice (thereby overflow/underflow problems are easily avoided),
and also to give accurate results even for the lowest values of l down to l=1.
Another virtue of the Debye expansions is that the limiting case of metals
becomes quite amenable to an analytical treatment in spherical geometry. We
first discuss the zero-frequency TE mode problem from a mathematical viewpoint
and then, as a physical input, invoke the actual dispersion relations. The
result of our analysis, based upon the adoption of the Drude dispersion
relation at low frequencies, is that the zero-frequency TE mode does not
contribute for a real metal. Accordingly, F turns out in this case to be only
one half of the conventional value at high temperatures. The applicability of
the Drude model in this context has however been questioned recently, and we do
not aim at a complete discussion of this issue here. Existing experiments are
low-temperature experiments, and are so far not accurate enough to distinguish
between the different predictions. We also calculate explicitly the
contribution from the zero-frequency mode for a dielectric. For a dielectric,
this zero-frequency problem is absent.Comment: 23 pages, LaTeX, 7 ps figures; expanded discussion, especially in
Sec. 5. To appear in Phys. Rev.
Casimir Force on a Micrometer Sphere in a Dip: Proposal of an Experiment
The attractive Casimir force acting on a micrometer-sphere suspended in a
spherical dip, close to the wall, is discussed. This setup is in principle
directly accessible to experiment. The sphere and the substrate are assumed to
be made of the same perfectly conducting material.Comment: 11 pages, 1 figure; to appear in J. Phys. A: Math. Ge
Casimir Force on Real Materials - the Slab and Cavity Geometry
We analyse the potential of the geometry of a slab in a planar cavity for the
purpose of Casimir force experiments. The force and its dependence on
temperature, material properties and finite slab thickness are investigated
both analytically and numerically for slab and walls made of aluminium and
teflon FEP respectively. We conclude that such a setup is ideal for
measurements of the temperature dependence of the Casimir force. By numerical
calculation it is shown that temperature effects are dramatically larger for
dielectrics, suggesting that a dielectric such as teflon FEP whose properties
vary little within a moderate temperature range, should be considered for
experimental purposes. We finally discuss the subtle but fundamental matter of
the various Green's two-point function approaches present in the literature and
show how they are different formulations describing the same phenomenon.Comment: 24 pages, 11 figures; expanded discussion, one appendix added, 1 new
figure and 10 new references. To appear in J. Phys. A: Math. Theo