  We report an unprecedented quantum criticality crossover representing two
different universal scaling behaviors in a Kitaev quantum magnetic material
$\alpha$-RuCl$_3$. $\alpha$-RuCl$_3$ presents both a symmetry breaking
antiferromagnetic order and a long-range entangled topological order of a
quantum spin liquid, and thus could be a candidate system for a new
universality class involving deconfined fractionalized excitations of the local
Z$_2$ fluxes and itinerant Majorana fermions. Theoretical analyses on the
inelastic neutron scattering and specific heat results demonstrate that
Wilson-Fisher-Yukawa-type 'conventional' weak-coupling quantum criticality in
high energy scales crosses over to heavy-fermion-type 'local' strong-coupling
one in low energy scales. Our findings provide deep insight on how the quantum
criticality evolves in fermion-boson coupled topological systems with different
types of deconfined fermions.
