ANISOTROPY OF THE SUPERCONDUCTING ENERGY-GAP IN URU2SI2 STUDIED BY POINT-CONTACT SPECTROSCOPY

The differential resistance dV/dI vs. applied voltage V for URu(?)2Si( 2)-normal-metal point-contacts (PCs) is investigated. For some PCs a c lear double-minimum structure is observed in dV/dI vs. V at zero bias well below the superconducting critical temperature T-c as expected fo r the Andreev reflection. The double minimum occurs only for PCs with suppressed antiferromagnetic (AF) features in dV/dI, in support of a r ecent model of the gap depression by AF order in the (a, b)-plane of t etragonal URu2Si2. A strong anisotropy of the reduced gap 2 Delta/kT(c ) and of B-c2 for PCs along the a and the c axis is also observed.