  While a specific kind of strange metal is increasingly found to be the
"normal" states in a wide variety of unconventional superconductors, its
microscopic origin is presently a hotly debated enigma. Using dynamical
mean-field theory (DMFT) based on hybridization expansion of continuous-time
quantum Monte-Carlo (CTQMC) solver for an extended two-band Hubbard model
(2BHM), we investigate the conditions underlying the emergence of such a metal.
Specifically, we tie strange metallicity to an orbital-selective Mottness in
2BHM or momentum-selective Mott phase (OSMP) in 2D Hubbard models inspired by a
cluster-to-orbital mapping. We find $(i)$ disparate spin and charge responses,
$(ii)$ fractional power-law behavior and $\omega/T$-scaling in the charge and
spin fluctuation responses, and $(iii)$ very good accord with optical
conductivity and nuclear magnetic relaxation rates in the slightly underdoped
normal states of cuprates and Fe-arsenides. We analyze the local problem using
bosonization to show that such anomalous responses arise from a lattice
orthogonality catastrophe specifically in the OSMP. Our work establishes the
intimate link between strange metallicity and selective Mottness in quantum
matter.
