  A typical f-electron Kondo lattice system Ce exhibits the well-known
isostructural transition, the so-called gamma-alpha transition, accompanied by
an enormous volume collapse. Most interestingly, we have discovered that a
topological-phase transition also takes place in elemental Ce, concurrently
with the gamma-alpha transition. Based on the dynamical mean-field theory
approach combined with density functional theory, we have unravelled that the
non-trivial topology in alpha-Ce is driven by the f-d band inversion, which
arises from the formation of coherent 4f band around the Fermi level. We
captured the formation of the 4f quasi-particle band that is responsible for
the Lifshitz transition and the non-trivial Z2 topology establishment across
the phase boundary. This discovery provides a concept of 'topology switch' for
topological Kondo systems. The 'on' and 'off' switching knob in Ce is versatile
in a sense that it is controlled by available pressure (around 1 GPa) at room
temperature.
