Large positive correlation between the effective electron mass and the multipolar fluctuation in the heavy-fermion metal Ce1 − x La x B6

For the last few decades, researchers have been intrigued by multipolar ordering phenomena and related quantum phasetransitions in heavy-fermion Kondo systems. However, a criticality induced by substitution level (x), temperature (T), or magneticfield (B) is poorly understood even in the prototypical material, Ce1−xLaxB6, despite a large collection of experimental results isavailable. In this work, we presentT–B,x–T, andx–Bphase diagrams of Ce1−xLaxB6(B|| [110]). These are completed by investigatingheat capacity, magnetocaloric effect (MCE), and elastic neutron scattering. A drastic increase of the Sommerfeld coefficientγ0,which is estimated from the heat capacity down to 0.05 K, is observed with increasingx. The preciseT–Bphase diagram including ahigh-entropy region is derived from the MCE analysis in which a knowledge beyond the equilibrium thermodynamics is involved.Finally, thex–Bphase diagram atT= 0, which supports the existence of a quantum critical point atx> 0.75, is obtained by the sameanalysis. A detailed interpretation of phase diagrams strongly indicates positive correlation between thefluctuating multipoles andthe effective electron mass