SQUIDs and Josephson junctions*

La_2−xBa_xCuO₄ (LBCO) exhibits a sharp drop in the transition temperature near x=1/8 doping, which coincides with charge order, spin order and the suppression of interlayer coupling between its CuO₂ planes. In this regime, charge, spin and superconducting orders are predicted to be intertwined into a pair-density wave (PDW) state, an ordered stripe phase characterized by sign changes in the superconducting order parameter between adjacent stripes. We present Josephson interferometry measurements of asymmetric SQUIDs incorporating crystals of LBCO at x=1/8 doping, from which we can extract the current-phase relation (CPR). We see features which are suggestive of a cancellation of the first-order Josephson tunneling and the onset of higher harmonics in the CPR, a signature of a pair-density wave state. We compare this data to measurements of LBCO devices at other dopings, as well as devices fabricated onto the striped material La_2-x-yEu_ySr_xCuO₄ (LESCO), another candidate for the formation of a PDW-state.