I think it may work the best to have kids (or the first one) during your PhD because that is a long period of time anyway, so it is more readily extended and a one with relatively most job stability (until you get tenure, but then it may be too late for biological reasons). It is easier if you...
The spectrum cannot be given by
E=v_Fk_F\pm v_F(\Delta^2+k^2)^{1/2}
because the units of \Delta and k are not the same. I tried rewriting the first term (linear kinetic energy) using operators shifted by k_F and then diagonalizing it, and I got
E=\frac{1}{2} (v_F k_F \pm (v_F^2 k^2 +...