Magnetic-field modulation of the Josephson effect between polycrystalline CeCu₂Si₂ and Al

Josephson critical current I_c between a polycrystalline CeCu₂Si₂ and Al has been measured for the junctions on a CeCu₂Si₂ surface. A dominant maximum peak at zero magnetic field is observed in the magnetic field H dependence of I_c, suggesting that the Josephson currents flowing from variously-oriented crystallites of CeCu₂Si₂ are in phase at H = 0. If CeCu₂Si₂ is in the d_x²−y²-wave state, in which the sign of the order parameter changes according to the crystallographic orientation, an s-wave component induced on the surface is considered as a possible origin of the s-wave-like behavior of I_c(H) patterns.