Quantum critical behaviour in doped Y bB12 studied by ab initio calculations

The Kondo insulator Y bB12 is known to undergo a transition to the metallic state with doping or under an external magnetic field. Within the virtual crystal approximation (VCA), we calculated the occupation of the Yb 4f and 5d shells, (n4f) and (n5d), as a function of doping of Y bB12 with the rare earths Tm and Lu. We found that n5d exhibits an anomalous change at the critical concentration xc of the dopant, in agreement with experiment (xc=0.5 for Y b1−xLuxB12 and xc=0.3 for Y b1−xTmxB12). We suggest that the critical behaviour seems to be strictly connected with the change of n5d and in consequence the change of the Yb valency.

► VCA approach.
► Mulliken analysis.
► Quantum critical behaviour in a doped Y bB12 in experiment and calculations.