  Transition metal oxides, in particular, 3d or 4d perovskites have provided
diverse emergent physics that originates from the coupling of various degrees
of freedom such as spin, lattice, charge, orbital, and also disorder. 5d
perovskites form a distinct class because they have strong spin-orbit coupling
that introduces to the system an additional energy scale that is comparable to
bandwidth and Coulomb correlation. Consequent new physics includes novel Jeff =
1/2 Mott insulators, metal-insulator transitions, spin liquids, and topological
insulators. After highlighting some of the phenomena appearing in
Ruddlesden-Popper iridate series Srn+1IrnO3n+1, we focus on the transport
properties of perovskite SrIrO3. Using epitaxial thin films on various
substrates, we demonstrate that metal-insulator transitions can be induced in
perovskite SrIrO3 by reducing its thickness or by imposing compressive strain.
The metal-insulator transition driven by thickness reduction is due to
disorder, but the metal-insulator transition driven by compressive strain is
accompanied by peculiar non-Fermi liquid behaviors, possibly due to the
delicate interplay between correlation, disorder, and spin-orbit coupling. We
examine various theoretical frameworks to understand the non-Fermi liquid
physics and metal-insulator transition that occurs in SrIrO3 and offer the
Mott-Anderson-Griffiths scenario as a possible solution.
