Tunneling in the ab plane of the high-${\mathit{T}}_{\mathit{c}}$ superconductor ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{8+\mathrm{\delta }}$ in high magnetic fields

Tunneling break junctions of single crystals of Bi-Sr-Ca-Cu-O show a reproducible superconducting-gap structure that can be fully described with a broadened BCS density of states. The obtained ratio between the energy gap Δ and the critical temperature ${\mathit{T}}_{\mathit{c}}$ amounts to 2Δ/${\mathit{T}}_{\mathit{c}}$=6.2. In a magnetic field up to 20 T, the conductance curve shows additional broadening but the energy gap remains constant. From a comparison of the magnetoresistance and tunneling data for different orientations of the magnetic field, it follows that the break junctions probe the superconducting properties in the ab plane. Both the magnetic field and temperature dependence of the tunneling characteristics are in agreement with the known dependences for the classical superconductors.