Order-parameter-node removal in the d-wave superconductor YBa 2 Cu 3 O 7-x in a magnetic field

摘要: We have measured the in-plane tunneling conductance of optimally doped ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$ films/In junctions as a function magnetic field and film orientation. In zero applied all samples exhibit bias peak (ZBCP) attributed to $d$-wave symmetry order parameter. formed on (110) oriented films, splitting ${\ensuremath{\delta}}_{\ensuremath{\downarrow}}(\mathrm{H})$ ZBCP in decreasing fields perpendicular ${\mathrm{CuO}}_{2}$ planes follows law ${\ensuremath{\delta}}_{\ensuremath{\downarrow}}(\mathrm{H})=\mathrm{A}\ensuremath{\cdot}{\mathrm{H}}^{1/2}$ with $\mathrm{A}=1.1{\mathrm{m}\mathrm{V}/\mathrm{T}}^{1/2}.$ This is obeyed up 16 T for thickness varying from 600 \AA{} (less than London penetration depth \ensuremath{\lambda}) 3200 (about twice \ensuremath{\lambda}). Since Meissner currents are negligible at smaller \ensuremath{\lambda}, this cannot be Doppler shift energy surface bound states. The data taken quantitatively consistent induced ${\mathrm{id}}_{\mathrm{xy}}$ component effect prominent increasing hysteresis splitting.