  Quantum Fisher information (QFI) of the reduced two-atom state is employed to
capture the quantum criticality of the superradiant phase transition in the
Dicke model in the infinite size and finite-$N$ systems respectively. The
analytical expression of the QFI of its ground state is evaluated explicitly.
And finite-size scaling analysis is performed with the large accessible system
size due to the effective bosonic coherent-state technique. We also investigate
the large-size scaling behavior of the scaled QFI of the reduced $N$-atom state
and show the accurate exponent.
