  In this letter, we propose an application of String Order Parameter (SOP),
commonly used in quantum spin systems, to identify symmetry-protected
topological phase (SPT) in fermionic systems in the example of the dimerized
fermionic chain. As a generalized form of dimerized model, we consider a
one-dimensional spin-1/2 XX model with alternating spin couplings. We employ
Jordan-Wigner fermionization to map this model to the spinless
Su-Schrieffer-Heeger fermionic model (SSH) with generalized hopping signs. We
demonstrate a phase transition between a trivial insulating phase and the
Haldane phase by the exact analytical evaluation of reconstructed SOPs which
are represented as determinants of Toeplitz matrices with the given generating
functions. To get more insight into the topological quantum phase transition
(tQPT) and microscopic correlations, we study the pairwise concurrence as a
local entanglement measure of the model. We show that the first derivative of
the concurrence has a non-analytic behaviour in the vicinity of the tQPT, like
in the second order trivial QPTs.
