  Charge density wave (CDW) can be characterized by the amplitude of its charge
modulation and the spatial phase coherence amongst CDW superlattice unit cells.
The phase coherence is usually guaranteed for weak-coupling CDW. However,
McMillan [Phys. Rev. B 16, 643 (1977)] predicted that in the strong coupling
regime, the phase fluctuation is strong and the coherence length of CDW could
be just a few superlattice unit cell size; a short-ranged CDW exists above the
transition, together with a CDW gap. In experiments, the short-ranged CDW with
small domains is often associated with defects, thus making it difficult to
identify the role of intrinsic phase fluctuations. Here, we report the
observation of a short-ranged CDW in Kagome magnet FeGe far below its CDW
transition temperature, and a pseudo gap in the non-CDW regions. Intriguingly,
it can be disrupted by gentle scans in a scanning tunneling microscope,
resulting in a metastable phase consisting of individual CDW nuclei independent
of defects. Our first-principle calculations show optical phonons in a sizable
momentum region soften similarly, which likely induces frustrations that could
destroy the phase coherence. These findings put the CDW state in FeGe in the
extreme strong-coupling limit with intrinsic quantum phase fluctuations, which
enriches the current understanding of CDW in the strong coupling regime.
