The upper critical field H" in layered superconductors is calculated from a microscopic theory in which the electrons are assumed to propagate freely within the individual layers subject to scattering off impurities and to propagate via tunneling between the layers. For the magnetic field parallel to the layers, there is a temperature T* & T, below which the normal cores of the vortices fit between the metallic layers, removing the orbital eff'ects as a mechanism for the quenching of superconductivity in the individual layers. In this temperature regime, H, 2~~i s thus determined by the combined eff'ects of Pauli paramagnetisrn and spin-orbit scattering, and for sufficiently strong spin-orbit scattering rates, ' H"~~{T =0) can greatly exceed the Chandrasekhar-Clogston Pauli limiting field H~. This unusual behavior is found to be most pronounced in the dirty limit for the electron propagation within the layers and when the electrons scatter many times in a given layer before tunneling to an adjacent layer. Our results are also discussed in light of the available experimental data.

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The THz radiation emitted from rectangular mesas of single-crystal Bi2Sr2CaCu2O 8+δ was studied using angular distribution measurements and Fourier transform infrared spectroscopy. Unlike the recent theoretical predictions, the results provide strong evidence for a dual-source mechanism in which the uniform and non-uniform parts of the ac-Josephson current act as electric and magnetic current sources, respectively. The latter synchronizes with cavity modes of the mesa with integral harmonics of the fundamental radiation.

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