Josephson vortex state across the phase diagram of La$_{2-x}$Sr$_x$CuO$_4$: a magneto-optics study

We present a detailed doping dependent study of the Josephson vortex state in La$_{2-x}$Sr$_x$CuO$_4$ using infrared spectroscopy. Magnetic field as high as 17 Tesla, applied along the CuO$_2$ planes, is found to suppress the Josephson plasmon in all measured samples. We find the strongest suppression in samples with dopings close to x=1/8 and attribute this effect to the spontaneous formation of in-plane charge inhomogenities (``stripes'') at this doping level. Several theoretical models of the Josephson vortex state are applied to explain the observed effects.