Point-contact spectroscopy of superconducting energy gap in DyNi2B2C
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The superconducting energy gap in DyNi2B2C has been investigated using a point-contact technique based on the Andreev reflection from a normal (N)–superconductor (S) boundary, where N is Ag. The observed differential resistance dV/dI is well described by the Blonder–Tinkham–Klapwijk (BTK) theory based on the BSC density of states with zero broadening parameter. Typically, the intensity of the gap structure amounts to several percentage of the normal state resistance, which is an order of magnitude less than predicted by the theory. For DyNi2B2C with Tc<TN (the Neel temperature), we found gap values satisfying the ratio of 2Δ0/kBTc=3.63±0.05 similar to other superconducting nickel-borocarbides, both nonmagnetic and magnetic with Tc≥TN. The superconducting gap nonlinearity is superimposed on the antiferromagnetic structure in dV/dI(V) which is suppressed at the magnetic field of the order of 3 T applied nominally in the ab-plane and temperature ≥11 K. The observed superconducting properties depend on the exact composition and structure at the surface of the crystal.
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