111 research outputs found
Comment on ''Surface-impedance approach solves problems with the thermal Casimir force between real metals''
In a recent paper, Geyer, Klimchitskaya, and Mostepanenko [Phys. Rev. A 67,
062102 (2003); quant-ph/0306038] proposed the final solution of the problem of
temperature correction to the Casimir force between real metals. The basic idea
was that one cannot use the dielectric permittivity in the frequency region
where a real current may arise leading to Joule heating of the metal. Instead,
the surface impedance approach is proposed as a solution of all contradictions.
The purpose of this comment is to show that (i) the main idea contradicts to
the fluctuation dissipation theorem, (ii) the proposed method to calculate the
force gives wrong value of the temperature correction since the contribution of
low frequency fluctuations is calculated with the impedance which is not
applicable at low frequencies. In the impedance approach the right result for
the reflection coefficients in the n=0 term of the Lifshitz formula is given.Comment: 4 page
The casimir free energy in high- and low-temperature limits
The problem with the temperature dependence of the Casimir force is investigated. We analyse high-temperature limit analytically making calculations at real frequencies. The purpose is to answer the questionwhy there is no continuous transition between real and ideal metals and why the result\ud
does not depend on the relaxation frequency. It is found that the contribution of evanescent s polarized fields is finite even for an infinitely small relaxation frequency (plasma model) and exactly cancels the contribution of propagating fields. For the ideal metal the evanescent fields do not contribute at all. The lowtemperature\ud
limit is analysed to establish behaviour of the entropy at T → 0. It is stressed that the nonlocal effects are important in this limit because the mean free path for electrons becomes larger than the field penetration depth.\ud
In this limit vF /a plays the role of the relaxation frequency, where vF is the Fermi velocity and a is the distance between plates. It is indicated that the\ud
Leontovich approximate impedance cannot be used for calculations because it is good for the description of propagating but not evanescent fields. It is found\ud
that due to nonlocality the Casimir entropy approaches zero at T → 0 when s polarization does not contribute to the classical part of the Casimir force
Graphene-on-silicon near-field thermophotovoltaic cell
A graphene layer on top of a dielectric can dramatically influence ability of
the material to radiative heat transfer. This property of graphene is used to
improve the performance and reduce costs of near-field thermophotovoltaic
cells. Instead of low bandgap semiconductors it is proposed to use
graphene-on-silicon Schottky photovoltaic cells. One layer of graphene absorbs
around 90% of incoming radiation and increases the heat transfer. This is due
to excitation of plasmons in graphene, which are automatically tuned in
resonance with the emitted light in the mid infrared range. The absorbed
radiation excites electron-hole pairs in graphene, which are separated by the
surface field induced by the Schottky barrier. For a quasi-monochromatic source
the generated power is one order of magnitude larger and efficiency is on the
same level as for semiconductor photovoltaic cells.Comment: 6 pages, 3 figures, to be published in Phys. Rev. Applie
Casimir effects in graphene systems: unexpected power laws
We present calculations of the zero-temperature Casimir interaction between
two freestanding graphene sheets as well as between a graphene sheet and a
substrate. Results are given for undoped graphene and for a set of doping
levels covering the range of experimentally accessible values. We describe
different approaches that can be used to derive the interaction. We point out
both the predicted power law for the interaction and the actual distance
dependence.Comment: 10 pages,5 figures, conferenc
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