  Inspired by holographic entanglement entropy, for geometries with non-zero
abelian charges, we define a quantity which is sensitive to the background
charges. One observes that there is a critical charge below that the system is
mainly described by the metric and the effects of the background charges are
just via metric's components. While for charges above the critical one the
background gauge field plays an essential role. This, in turn, might be used to
define an order parameter to probe phases of a system with fractionalized
charges.
