  The normal state of the recently discovered Iron Selenide (FeSe)-based
superconductors shows a range of inexplicable features. Along with bad-metallic
resistivity, characteristic pseudogap features and proximity to insulating
states, reminiscent of the underdoped high-Tc cuprates, mark these systems as
strongly correlated non-Fermi Liquid metals. Here, using the first-principles
LDA+DMFT method, we show how strong multi-orbital correlation-induced
orbital-selective Mott-like physics leads to an orthogonality catastrophe
underpinning these inexplicable incoherent features. Excellent agreement with a
range of resistivity and Seebeck data strongly support our proposal. We discuss
pseudogap regime microscopically, along with implications for the nature of the
instability at lower T, and propose that related systems could be of use in
thermoelectric devices.
