PHYSICAL REVIEW LETTERS 30 AUGUST 1976 ducting microbridge irradiated by microwaves, can be understood by the fact that a low-energy quasiparticle is more effective in blocking the pairing process than higher energy quasiparticles. Here, our calculation shows that a superconductor irradiated by microwave can actually have a quasiparticle density smaller than its equilibrium value. This can also lead to an increase in the energy gap and critical current.18 Please note that this excess quasiparticle density is not the same as that defined in Ref 0 7 0 19 We believe that the flat I (V) characteristic for a lowtemperature nonequilibrium tunneling junction found byThe resistivity of an aggregated film of conducting material has been well known to exhibit an abrupt fall over several orders of magnitude within a very small interval of the effective thickness of an ultrathin film. The effective thickness at which the resistivity begins to fall is different for different film materials and for different substrate conditions, especially the substrate temperature. Among these factors, the fraction of the substrate surface area covered by the aggregates or islands or so-called particles would be very important from the point of view of the explanation of the phenomena by the theory of percolation. Neugebauer 1 displayed such a resistivity dependence on thickness of mercury films at various temperatures. Hill 2 also reported a series of papers specifically on the electrical conduction in ultrathin metal films. Among a number of investigators, Ambegaokar, Halperin, and Langer 3 employed a percolation approach to the conductivity dependence on temperature in a three-dimensional bulk disordered system of amorphous semiconductor and explained the T" 1/4 law of hopping conductivity very successfully. Pollak 4 further treated the dc conductivity by percolation theory and disParker (Ref. 10) for eV^> (2A*) indicates that, in fact, the excess quasiparticle density 6N can be determined from the measurement of the excess current in the plateau region. Furthermore, our analysis also shows that for an SIS tunnel junction with only one of the superconducting films being driven out of equilibrium, <5/ a -AA*6N and 6/ & -0 in the high-voltage limit. Therefore, without knowing whether one or both of the thin films are out of equilibrium, the total excess quasiparticle density determined from the plateau value of the excess current at eV ^ 2 A* can be off by a factor of 2, cussed cases including the T" 1/4 law and the activated conductivity. Attempting to perform a decisive experiment on the relation between percolation theory and electrical conductivity Last and Thouless 5 punched macroscopic holes in a sheet of colloidal graphite paper and measured its conductance. They claimed the conductivity behaved quite differently from the predictions of percolation theory. Their problem was later resolved by Kirkpatrick 6 as due to the differences between the percolation probability and the conductance of the sample. Watson and Leath 7 measured ...

The scattering of light by a spheroidal metal particle has been newly treated by use of the technique of the multipole expansion of radiation fields from the induced polarization and the associated current and magnetization, which are now considered as radiation sources. The relation between the polarization and the incident field is most simply obtained by using the long-wavelength approximation and a radiation-damping correction. The various orders of electricand magnetic-multipole coefficients of scattered fields have been separately calculated. Part of our calculated results confirm and thus justify the well-known features that the electric-dipole term gives the dominant contribution and that the magnitudes of multipole coefficients decrease monotonically with the increasing-order number of the multipoles. Some new features concerning the accuracy and the limitation of the radiation-damping correction are discussed against the depolarization factor of the spheroid. For a small sphere, the results reduce to the famous Rayleigh scattering, as expected. Results for larger spheres are compared with those of an exact electrodynamical calculation.

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There is controversy regarding the surface enhancement of Raman scattering due to liquid Hg, and the enhancement of benzoic acid molecules adsorbed on liquid Hg has been determined to be essentially zero. However, if the noise error bar is taken into account, the maximum enhancement is estimated to be less than 30. The same enhancement was observed when the temperature was reduced in solidifying liquid Hg.

Surface-enhanced Raman scattering from crystal vibrational modes of a Sb film rather than from vibrational modes of individual molecules has been observed for the first time to our knowledge. A ~20x enhancement of the longitudinal-optical mode (150 cm(-1)) in the Raman spectra of crystalline Sb films deposited on silver-island films was obtained. The excitation profiles, as well as the dependence of Raman intensity on the thickness of Ag films, were studied.