  Scanning tunneling spectroscopy was performed on (110)-oriented thin films of
Ca-overdoped Y$_{0.95}$Ca$_{0.05}$Ba$_2$Cu$_3$O$_{7-\delta}$ at 4.2K, to probe
the local evolution of Andreev$-$Saint-James surface states in a c-axis
magnetic field. In zero field, we observed conductance spectra with
spontaneously-split peaks and spectra with unsplit zero-bias peaks. The former
showed enhanced splitting with field, and the latter showed threshold splitting
above finite fields. Although both field evolutions can be described in terms
of screening and orbital supercurrents, within the framework of $d\pm i\alpha$
pairing ($d$=$d_{x^2-y^2}$; $\alpha$=$d_{xy}$,$s$), the enhanced splitting is
consistent with only the $d$ + $i\alpha$ state. Our results have direct
implications on the stability of broken time-reversal symmetry in cuprate
superconductors.
