Taking into account the possibility of particle-antiparticle pair production, we have investigated the onset of Bose-Einstein condensation in an ideal relativistic Bose gas confined to restricted geometries. Through a...
Taking into account the possibility of particle-antiparticle pair production, we have investigated the onset of Bose-Einstein condensation in an ideal relativistic Bose gas confined to restricted geometries. Through an extensive use of the Poisson summation formula, we have carried out an explicit evaluation of the summations over states appearing in the problem, which enables us to make a rigorous analysis of the temperature dependence of the thermogeometric parameter y of the system in the case of a cubical enclosure under periodic boundary conditions. This, in turn, leads us to determine the growth of the condensate fraction ρ0ρ as a smooth function of temperature from T≳Tc down to T=0 K. Finite-size corrections to the standard bulk results are obtained in explicit terms and are shown to be in complete agreement with the Fisher-Barber scaling theory for such effects. In the end, special geometries, such as narrow channels and thin films, are also examined.
An apparatus is described for measuring Seebeck coefficients in semiconducting thin‐film samples with resistances as high as 101 1 Ω. A temperature gradient ΔT is produced across the sample by means of differential...
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An apparatus is described for measuring Seebeck coefficients in semiconducting thin‐film samples with resistances as high as 1011 Ω. A temperature gradient ΔT is produced across the sample by means of differential optical heating of the ends of the sample. The Seebeck voltage ΔV is measured using a specially designed amplifier circuit with an input impedance of 1013 Ω. The Seebeck coefficient is obtained from the slope of the plot of ΔV vs ΔT.
The effect of paramagnetic impurities in anisotropic superconductors is investigated with use of the Shiba-Rusinov theory for the impurities and the Eliashberg formalism for the host superconductor. The analytical exp...
The effect of paramagnetic impurities in anisotropic superconductors is investigated with use of the Shiba-Rusinov theory for the impurities and the Eliashberg formalism for the host superconductor. The analytical expressions for the transition temperature Tc and the specific-heat jump ΔC are derived with the use of the square-well model for the electron-phonon interaction. Considered as a function of the spin-flip scattering rate α, the quantities TcTc0 and ΔCΔC0 depend on the microscopic parameters λ, ωD, and μ* of the host material. The dependence on the material parameters becomes insignificant if the above properties are plotted versus ααcr or if ΔCΔC0 versus TcTc0 is studied. (Tc0 and ΔC0 are values of Tc and ΔC, respectively, in the absence of impurities, αcr is the value of α for which Tc becomes zero, λ is electron-phonon—interaction parameter, ωD is the Debye frequency, and μ* is the Coulomb pseudopotential.)
Shiba-Rusinov theory of magnetic impurities in isotropic superconductors beyond the s-wave scattering is generalized by using the Eliashberg formalism. The analytical expressions for the transition temperature Tc and ...
Shiba-Rusinov theory of magnetic impurities in isotropic superconductors beyond the s-wave scattering is generalized by using the Eliashberg formalism. The analytical expressions for the transition temperature Tc and the specific-heat jump ΔC are given using the square-well model for the electron-phonon interaction. Taken as a function of the impurity concentration, the quantities TcTc0 and ΔCΔC0 depend on the microscopic parameters λ, μ*, and ωD of the host material. However, this dependence is absent if one plots the above properties versus the normalized impurity concentration ααcr or if ΔCΔC0 vs TcTc0 is studied. (Tc0 and ΔC0 are values of Tc and ΔC, respectively, in the absence of impurities; λ is the electron-phonon interaction parameter, μ* the Coulomb pseudopotential, and ωD the Debye cutoff frequency; α is the spin-flip scattering rate; αcr is the value of α for which T becomes zero.)
We derive a formula for calculating the free-energy difference between the superconducting and the normal states of a strong-coupling superconductor with localized states within the gap (induced by magnetic impurities...
We derive a formula for calculating the free-energy difference between the superconducting and the normal states of a strong-coupling superconductor with localized states within the gap (induced by magnetic impurities). The present formula is a generalization of the one given by Bardeen and Stephen (for the electron-phonon systems) to include the effect of Shiba-Rusinov impurities.
An electronic analog simulation of two coupled superconducting microbridges is shown to give similar results to the numerical solution. For strongly coupled microbridges some new phenomena are revealed. Strongly coupl...
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An electronic analog simulation of two coupled superconducting microbridges is shown to give similar results to the numerical solution. For strongly coupled microbridges some new phenomena are revealed. Strongly coupled thin‐film microbridges were prepared by a new technique and their current‐voltage characteristics confirm some of the predictions that are indicated by the analog simulation.
Superconducting microbridges with lenghts ranging from shorter than to longer than the coherence length have been fabricated. Those microbridges whose length is longer than the coherence length do show a dynamic enhan...
Superconducting microbridges with lenghts ranging from shorter than to longer than the coherence length have been fabricated. Those microbridges whose length is longer than the coherence length do show a dynamic enhanced critical current in accordance with the theory of Schmid, Schön, and Tinkham. Those microbridges whose length is shorter than the coherence length do not exhibit a dynamically enhanced critical current and a possible reason for its absence is that the order parameter is depressed in the banks adjacent to the microbridge.
A measurement system for the current–voltage characterization of solar cells has been developed. The instrument is based on an Intel 8088 microprocessor, which allows for enhanced data collection and storage, as well...
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A measurement system for the current–voltage characterization of solar cells has been developed. The instrument is based on an Intel 8088 microprocessor, which allows for enhanced data collection and storage, as well as automated measurement control. A high‐power analog supply makes measurements in the range of ?10 to +10 V and ?0.75 to 0.75 A possible, and provides the capability for sinking currents up to 1 A at +10‐V output. Measured data may be transferred to an IBM personal computer for immediate display, and for consequent analysis (to obtain the characteristic parameters). The system provides a rapid, effective I–V curve measurement and analysis method for many devices, and experimental solar cells in particular.
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