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Abstract

Interlayer transport in high-TC cuprates is mediated by superconducting tunneling across the CuO2 planes. For this reason, the terahertz frequency optical response is dominated by one or more Josephson plasma resonances and becomes highly nonlinear at fields for which the tunneling supercurrents approach their critical value, IC. These large terahertz nonlinearities are in fact a hallmark of superconducting transport. Surprisingly, however, they have been documented in La2−xBaxCuO4 also above TC for doping values near x=1/8, and interpreted as an indication of superfluidity in the stripe phase. Here, Electric Field Induced Second Harmonic (EFISH) is used to study the dynamics of time-dependent interlayer voltages when La2−xBaxCuO4 is driven with large-amplitude terahertz pulses, in search of other characteristic signatures of Josephson tunnelling in the normal state. We show that this method is sensitive to the voltage anomalies associated with 2π Josephson phase slips, which near x=1/8 are observed both below and above TC. These results document a new regime of nonlinear transport that shares features of sliding charge-density-waves and superconducting phase dynamics.