  High pressure provides a powerful means for exploring unconventional
superconductivity which appears mostly on the border of magnetism. Here we
report the discovery of pressure-induced heavy fermion superconductivity up to
2.5 K in the antiferromanget CeAu2Si2 (TN ~ 10 K). Remarkably, the magnetic and
superconducting phases are found to overlap across an unprecedentedly wide
pressure interval from 11.8 to 22.3 GPa. Moreover, both the bulk Tc and TM are
strongly enhanced when increasing the pressure from 16.7 to 20.2 GPa. Tc
reaches a maximum at a pressure slightly below pc ~ 22.5 GPa, at which magnetic
order disappears. Furthermore, the scaling behavior of the resistivity provides
evidence for a continuous delocalization of the Ce 4f-electrons associated with
a critical endpoint lying just above pc. We show that the maximum Tc of
CeAu2Si2 actually occurs at almost the same unit-cell volume as that of
CeCu2Si2 and CeCu2Ge2, and when the Kondo and crystal field splitting energies
becomes comparable. Dynamical mean-filed theory calculations suggest that the
peculiar behavior in pressurized CeAu2Si2 might be related to its Ce 4f-orbital
occupancy. Our results not only provide a unique example of the interplay
between superconductivity and magnetism, but also underline the role of orbital
physics in understanding Ce-based heavy fermion systems.
