  The clathrate-like or caged compounds have attracted continuing interest due
to their structural flexibility as well as fertile physical properties. Here we
report a pressure-induced reemergence of superconductivity in BaIr2Ge7 and
Ba3Ir4Ge16, two new caged superconductors with two-dimensional building blocks
of cage structures. After suppressing the ambient-pressure superconducting
(SC-I) state, a new superconducting (SC-II) state emerges unexpectedly, with Tc
increased to a maximum of 4.4 K and 4.0 K for BaIr2Ge7 and Ba3Ir4Ge16,
respectively. Combined with high-pressure synchrotron x-ray diffraction and
Raman measurements, we propose that the reemergence of superconductivity in the
caged superconductors can be ascribed to a pressure-induced phonon softening
linked to the cage shrink.
