Reflectivity and Microwave Absorption in Crystals with Alternating Intrinsic Josephson Junctions

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We compute the frequency and magnetic field dependencies of the reflectivity R(ω) in layered superconductors with two alternating intrinsic Josephson junctions with different critical current densities and quasiparticle conductivities for the electric field polarized along the c axis. The parameter α describing the electronic compressibility of the layers and the charge coupling of neighboring junctions was extracted for the SmLa_1-xSr ︀ₓCuO ︀_4-δ superconductor from two independent optical measurements, the fit of the loss function L(ω) at zero magnetic field and the magnetic field dependence of the peak positions in L(ω). The experiments are consistent with a free electron value for α.