Tunneling spectra of break junctions involving Nb₃Sn

The electronic gap structure of Nb₃Sn was measured by the break-junction (BJ) tunneling technique. The superconducting gap values are estimated to be in the range 2Δ = 4-5.5 meV at T = 4.2 K as follows from the observed distinct conductance peaks. In addition to the superconducting gap structure, we observed reproducible hump-like structures at the biases of about ± 20 and ± 50 mV. Such a coexistence of gap and hump structures resembles the situation found in the high-T_c copper-oxide superconductors. Above the superconducting critical temperature T_c ∼ 18 K, the humps appear as the only gap-like structures. Their possible origin is discussed in connection to the structural phase transition occurring in Nb₃Sn.