Superconductivity and the Josephson effect in a periodic array of Nb-InAs-Nb junctions

We have applied high-frequency radiation to a one-dimensional array of superconducting-normal-superconducting junctions, comprised of Nb-2DInAs-Nb, and observed Shapiro steps in the I-V curve which are dominated by a step at V = h nu/4e, half the voltage of the usual AC Josephson Effect. This result is discussed in view of a coupling between the Nb stripes that differs from the usual j(c) sin Phi form, The zero-bias resistance of the sample is finite and increases exponentially with temperature. The Shapiro steps, however, persist up to the Nb transition temperature, These results imply that the finite resistance of the sample originates from excitations in the superconducting slate.