Order-parameter-node removal in the d-wave superconductor YBa2Cu3O7−x in a magnetic field

Abstract

We have measured the in-plane tunneling conductance of optimally doped YBa2Cu3O7−x films/In junctions as a function of magnetic field and film orientation. In zero applied field all samples exhibit a zero bias conductance peak (ZBCP) attributed to the d-wave symmetry of the order parameter. In junctions formed on (110) oriented films, the splitting δ↓(H) of the ZBCP in decreasing fields applied perpendicular to the CuO2 planes follows the law δ↓(H)=A⋅H1/2 with A=1.1mV/T1/2. This law is obeyed up to 16 T for film thickness varying from 600 Å (less than the London penetration depth λ) up to 3200 Å (about twice λ). Since Meissner currents are negligible in decreasing fields and at thickness smaller than λ, this splitting cannot be attributed to a Doppler shift of zero energy surface bound states. The data taken in decreasing fields is quantitatively consistent with a field induced idxy component of the order parameter. The effect of the Doppler shift is prominent in data taken in increasing fields and in the field hysteresis of the splitting.

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