Small Magnetic Fields Arrest the Josephson Plasma Resonance in La$_{2-x}$Sr$_{x}$CuO$_{4 }$for x=1/8

We report on a study of the far infrared interlayer response in a La$_{2-x}$Sr$_{x}$CuO$_{4}$ (La214) crystal at the x=1/8 doping. A magnetic field up to 8 Tesla, applied perpendicular to the CuO$_{2}$ planes, is found to completely suppress the Josephson plasma resonance (JPR) in sharp contrast to the mild suppression of the JPR if the field is applied along the planes. We suggest that this anomalous sensitivity of the JPR feature to modest fields for H$\vert $c-axis is due to the interaction of in-plane charge inhomogeneities with vortices that form in the CuO$_{2}$ planes.