  The spontaneous appearance of nematicity, a state of matter that breaks
rotation but not translation symmetry, is one of the most intriguing property
of the iron based superconductors (Fe SC), and has relevance for the cuprates
as well. Establishing the critical electronic modes behind nematicity remains
however a challenge, because their associated susceptibilities are not easily
accessible by conventional probes. Here using FeSe as a model system, and
symmetry resolved electronic Raman scattering as a probe, we unravel the
presence of critical charge nematic fluctuations near the structural / nematic
transition temperature, T$_S\sim$ 90 K. The diverging behavior of the
associated nematic susceptibility foretells the presence of a Pomeranchuk
instability of the Fermi surface with d-wave symmetry. The excellent scaling
between the observed nematic susceptibility and elastic modulus data
demonstrates that the structural distortion is driven by this d-wave
Pomeranchuk transition. Our results make a strong case for charge induced
nematicity in FeSe.
