The 0$^+_2$ state in $^{34}$Si has been populated at the {sc Ganil/Lise3} facility through the $beta$-decay of a newly discovered 1$^+$ isomer in $^{34}$Al of 26(1) ms half-life. The simultaneous detection of $e^+e^-$ pairs allowed the determination
of the excitation energy E(0$^+_2$)=2719(3) keV and the half-life T$_{1/2}$=19.4(7) ns, from which an electric monopole strength of $rho^2$(E0)=13.0(0.9)$times10^{-3}$ was deduced. The 2$^+_1$ state is observed to decay both to the 0$^+_1$ ground state and to the newly observed 0$^+_2$ state (via a 607(2) keV transition) with a ratio R(2$^+_1$$rightarrow0^+_1/2^+_1$$rightarrow0^+_2$)=1380(717). Gathering all information, a weak mixing with the 0$^+_1$ and a large deformation parameter of $beta$=0.29(4) are found for the 0$^+_2$ state, in good agreement with shell model calculations using a new {sc sdpf-u-mix} interaction allowing textit{np-nh} excitations across the N=20 shell gap.
The energies of the excited states in very neutron-rich $^{42}$Si and $^{41,43}$P have been measured using in-beam $gamma$-ray spectroscopy from the fragmentation of secondary beams of $^{42,44}$S at 39 A.MeV. The low 2$^+$ energy of $^{42}$Si, 770(1
9) keV, together with the level schemes of $^{41,43}$P provide evidence for the disappearance of the Z=14 and N=28 spherical shell closures, which is ascribed mainly to the action of proton-neutron tensor forces. New shell model calculations indicate that $^{42}$Si is best described as a well deformed oblate rotor.
