アイテム詳細

要旨

Interlayer transport in high-T_C 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 I_C. These large terahertz nonlinearities are in fact a hallmark of superconducting transport. Surprisingly, however, they have been documented in La_2−xBa_xCuO₄ (LBCO) also above T_C for doping values near x=1/8 and interpreted as an indication of superfluidity in the stripe phase. Here, electric-field-induced second harmonic is used to study the dynamics of time-dependent interlayer voltages when LBCO is driven with large-amplitude terahertz pulses, in search of other characteristic signatures of Josephson tunneling in the normal state. We show that this method is sensitive to the voltage anomalies associated with 2π Josephson phase slips, which near x=18 are observed both below and above T_C. These results document a regime of nonlinear transport that shares features of fluctuating stripes and superconducting phase dynamics.