On relation between unitary gauge and gauge given by $\xi$-limiting process

It is shown that in general the gauge given by the limit of $\xi \to 0$ in $R_{\xi }$ gauge does not necessarily agree with the unitary gauge by examining the symmetry breaking of two steps from ${\mathrm{S}\mathrm{U}(3)\otimes \mathrm{U}(1)}_N$ to ${\rm SU(2) \otimes U(1)}Y$andthento${\rm U(1)}{em}$.