Near coincidence of metal-insulator transition and quantum critical fluctuations: Electronic ground state and magnetic order in Fe1−xCoxSi

We present a detailed study of the electronic and magnetic ground-state properties of Fe_1-xCoₓSi using a combination of macroscopic and microscopic experimental techniques. From these experiments we quantitatively characterize the metal-insulator transition and magnetic/nonmagnetic quantum phase transition occurring at low-doping levels in Fe_1-xCoₓSi. From our study, we find a surprising closeness of the critical composition of the metal-insulator transition at xMIT=0.014 and the quantum phase transition at xLRO~0.024-0.031. This suggests that these effects are cooperative and depend on each other.