Mutual information for fermionic systems

We study the behavior of mutual information (MI) in various quadratic fermionic chains, with and without pairing terms both short- long-range hoppings. The models considered include short-range limit versions Kitaev model as well, also cases which area law for entanglement entropy is - logarithmically or non-logarithmically violated. In all surveyed, when violated at most logarithmically, MI a monotonically increasing function conformal four-point ratio x. Where non-logarithmic violations are present, non-monotonic features can be observed ratio, well other natural combinations parameters, found not to sufficient capture whole structure collapse onto single curve. interpret this sign that peaks related non-universal spatial configuration Bell pairs. For exhibiting perfect volume law, vanishes identically. vanishing x -> 0 it remains zero up finite gapped case. general, larger range corresponds reduction small A discussion comparison results obtained by AdS/CFT correspondence strong coupling presented.