Isovector dipole strength in nuclei with extreme neutron excess

The E1 strength is systematically analyzed in very neutron-rich Sn nuclei, beyond Sn-132 until Sn-166, within the relativistic quasiparticle random phase approximation. The great neutron excess favors the appearance of a deformed ground state for Sn142-162. The evolution of the low-lying strength in deformed nuclei is determined by the interplay of two factors, isospin asymmetry and deformation: while greater neutron excess increases the total low-lying strength, deformation hinders and spreads it. Very neutron rich deformed nuclei may not be as good candidates as spherical nuclei like Sn-132 for the experimental study of low-lying E1 strength.