Doppler shift of the andreev bound states at the YBCO surface

The effect of applied magnetic field on the zero-bias conductance peak (ZBCP) observed in tunneling spectra of YBCO reveals the number of states is conserved; the splitting magnitude depends upon field orientation and hysteresis. Both the conservation and anisotropy are consistent with the ZBCP resulting from quasiparticle (QP) Andreev bound states at the YBCO surface with a Doppler shift arising from the scalar product between the QP velocity and superfluid momentum, v_F·;P_s. The hysteresis is consistent with the effects of strong vortex pinning on the surface screening currents.