Gapless Superconductivity in Bi 2 Sr 2 CaCu 2 O 8

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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 - EF| 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 EF.