Effects of magnetic vortices upon Josephson Plasma Wave propagation in Bi₂Sr₂CaCu₂O₈ crystals

Extremely anisotropic cuprate superconductors contain 'intrinsic' Josephson junctions, stacked along the crystalline c-axis. Consequently, these compounds can support the propagation of Josephson plasmons at frequencies of hundreds of GHz or more. These plasmons primarily transport energy along the CuO₂ planes via oscillating Josephson tunneling currents. In Bi₂Sr₂CaCu₂O₈, it is predicted that Josephson plasmons could propagate over distances of centimeters, due to the highly underdamped nature of the Josephson oscillations in this material. This phenomenon could have technological applications, such as in highly efficient mixers and detectors for terahertz frequencies.



We observe the propagation of Josephson plasma waves at 0.45 THz through an optimally-doped Bi₂Sr₂CaCu₂O₈ slab with diameter 5 mm and thickness 0.21 mm, cut from a TSFZ growth rod and consisting of multiple single crystals. Our zero-field results imply a plasmon decay length that is 0.4 mm at 85 Kelvin (slightly below T_c) and peaks at 0.9 mm at 25 Kelvin. We also find that the plasmon decay length can be either strongly enhanced or suppressed by applied magnetic fields of the order of a few tens of Gauss, depending upon the magnitude of the field. Applying a field of 25 G increases the decay length to approximately 1 cm or more at 4.4 K. We provisionally attribute this behavior to transmission of THz energy via pinned vortex lattices in the crystals of our sample.