  Isomer spectroscopy of heavy neutron-rich nuclei beyond the N=126 closed
shell has been performed for the first time at the Radioactive Isotope Beam
Factory of the RIKEN Nishina Center. New millisecond isomers have been
identified at low excitation energies, 985.3(19) keV in 213Tl and 874(5) keV in
215Tl. The measured half-lives of 1.34(5) ms in 213Tl and 3.0(3) ms in 215Tl
suggest spins and parities 11/2- with the single proton-hole configuration
h11/2 as leading component. They are populated via E1 transitions by the decay
of higher-lying isomeric states with proposed spin and parity 17/2+,
interpreted as arising from a single s1/2 proton hole coupled to the 8+
seniority isomer in the (A+1)Pb cores. The lowering of the 11/2- states is
ascribed to an increase of the h11/2 proton effective single-particle energy as
the second g9/2 orbital is filled by neutrons, owing to a significant reduction
of the proton-neutron monopole interaction between the h11/2 and g9/2 orbitals.
The new ms-isomers provide the first experimental observation of shell
evolution in the almost unexplored N>126 nuclear region below doubly-magic
208Pb.
