Near coincidence of metal-insulator transition and quantum critical fluctuations: Electronic ground state and magnetic order in ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x\mathrm{Si}$

We present a detailed study of the electronic and magnetic ground-state properties of ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x\mathrm{Si}$ 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 ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x\mathrm{Si}$. From our study, we find a surprising closeness of the critical composition of the metal-insulator transition at $x_{\mathrm{MIT}}=0.014$ and the quantum phase transition at $x_{\mathrm{LRO}}\sim 0.024-0.031$. This suggests that these effects are cooperative and depend on each other.