  It is shown that intermittency, a self-similar correlation with respect to
the size of the phase space volume, is sensitive to critical density
fluctuations of baryon numbers in a system belonging to the three-dimensional
(3D) Ising universality class. The relation between intermittency index and
relative baryon density fluctuation is obtained. We thus suggest that measuring
the intermittency in relativistic heavy-ion collisions could be used as a good
probe of density fluctuations associated with the QCD critical phenomena. From
recent preliminary results on neutron density fluctuations in central Au + Au
collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV at
RHIC/STAR, the collision energy dependence of intermittency index is extracted
and shows a non-monotonic behavior with a peak at around 20 - 27 GeV,
indicating that the strength of intermittency becomes the largest in this
energy region. The transport UrQMD model without implementing critical physics
cannot describe the observed behavior.
