  The energy levels of quasiparticles in superconductors experience Doppler
shifts due to the influence of a finite current flow. The influence of the
Doppler shift is particularly pronounced in unconventional superconductors with
gap nodes. In the case of a normal/insulator/superconductor junction of
$d$-wave superconductors, a zero-bias conductance peak exhibits a peak shift in
an applied magnetic field. Although the shifts have been detected in
experiments, the shifts showed different field responses depending on each
experiment. In this paper, we evaluate the magnitude of the shift based on
realistic junction shapes to elucidate the origin of the variability in
experimental Doppler shifts. We find that the peak shift depends on the
junction shape; the splitting is significantly suppressed when the junction is
formed at a protruding position. Also, the shift is suppressed by the
penetration of magnetic flux quanta, resulting in a nonlinear response to the
magnetic field. The present results explain the origin of the variability in
experimental Doppler shifts.
