  Sr2IrO4 is an archetypal spin-orbit-coupled Mott insulator with an
antiferromagnetic state below 240 K. Here we report results of our study on
single crystals of Sr2Ir1-xFexO4 (0<x<0.32) and Sr2Ir1-xCoxO4 (0<x<0.22). Fe
doping retains the antiferromagnetic state but simultaneously precipitates an
emergent metallic state whereas Co doping causes a rapid collapse of both the
antiferromagnetic and Mott states, giving rise to a confined metallic state
featuring a pronounced linearity of the basal-plane resistivity up to 700 K.
The results indicate tetravalent Fe4+(3d4) ions in the intermediate spin state
with S=1 and Co4+(3d5) ions in the high spin state with S=5/2 substituting for
Ir4+(5d5) ions in Sr2IrO4, respectively. The effective magnetic moment closely
tracks the N\'eel temperature as doping increases, suggesting that the spin
state of the dopant predominately determines the magnetic properties in doped
Sr2IrO4. Furthermore, all relevant properties including charge-carrier density
(e.g., 1028/m3), Sommerfeld coefficient (e.g., 19 mJ/mole K2) and Wilson ratio
(e.g., 2.6), consistently demonstrates a metallic state that is both robust and
highly correlated in the two systems, arising from the percolation of bound
states and the weakening of structural distortions. This study strongly
suggests that the antiferromagnetic and Mott states merely coexist in a
fortuitous manner in Sr2IrO4.
