Gapless Superconductivity in Bi 2 Sr 2 CaCu 2 O 8

Abstract

Break-junction tunneling results are evaluated to obtain the excitation spectrum or density of states (DOS) in the superconducting state of Bi₂Sr₂CaCu₂O₈. At low temperatures the DOS follows N(E) ~ |E - E_F| for energies close to the Fermi level and exhibits peaks separated by 2Δ = 72 meV. As the temperature is increased, the peak-to-peak distance decreases slightly and the states in between are rapidly filled up. There is also a temperature-independent feature in the DOS, with an energy scale ≥ 200 meV, most likely symmetric about E_F.