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

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hether the node in the order parameter characteristic of a d-wave superconductor can or cannot be removed by an applied magnetic field has been a subject of debate in recent years. Thermal conductivity results on the high Tc superconductor Bi₂Sr₂CaCu₂O₈ originally explained by Laughlin in terms of such a node removal were complicated by hysteresis effects, and judged inconclusive. We present new tunneling data on YBa₂Cu₃O₇₋ₓ that support the existence of the node removal effect, under specific orientations of the sample's surfaces and magnetic field. We also explain the hysteretic behavior and other previous tunneling results so far not understood satisfactorily, attributing them to a combination of node removal and Doppler shift of low energy surface bound states.