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

Abstract

For the last few decades, researchers have been intrigued by multipolar ordering phenomena and related quantum phase transitions in heavy-fermion Kondo systems. However, a criticality induced by substitution level (x), temperature (T), or magnetic field (B) is poorly understood even in the prototypical material, Ce1−x La x B6, despite a large collection of experimental results is available. In this work, we present T–B, x–T, and x–B phase diagrams of Ce1−x La x B6 (B || [110]). These are completed by investigating heat capacity, magnetocaloric effect (MCE), and elastic neutron scattering. A drastic increase of the Sommerfeld coefficient γ0, which is estimated from the heat capacity down to 0.05 K, is observed with increasing x. The precise T–B phase diagram including a high-entropy region is derived from the MCE analysis in which a knowledge beyond the equilibrium thermodynamics is involved. Finally, the x–B phase diagram at T = 0, which supports the existence of a quantum critical point at x > 0.75, is obtained by the same analysis. A detailed interpretation of phase diagrams strongly indicates positive correlation between the fluctuating multipoles and the effective electron mass.

Crystalline electric field of Ce in trigonal symmetry: CeIr3Ge7 as a model case

“…The ordering has been found to be usually antiferromagnetic (AFM), but recently several ferromagnetic systems were discovered [14]. Depending on the CEF, Ce-based systems may also exhibit multipolar order: For instance, in the highsymmetry cubic structure the CEF yields to a quartet Γ 8 ground state which allows quadrupolar and AFM order like in Ce 3 Pd 20 Ge 6 [3,15] or Ce 1−x La x B 6 [16,17].…”

Doping-induced redistribution of magnetic spectral weight in the substituted hexaborides Ce1−xLaxB6 and Nikitin1, Portnichenko2, Dukhnenko3 et al. 2018Phys. Rev. B123160View full textAdd to dashboardCite

“…The data were analyzed and symmetrized using DAVE [75] and HORACE [76] software. The La-substituted cerium hexaborides Ce 1−x La x B 6 have been a subject of active research for a long time [25, 31, 39-41, 45-47, 57-61, 67, 77-79], and complete characterization of all La substituted Ce 1−x La x B 6 single crystals, which we used in this work, was already done previously [47,61]. However, there have been only very few works devoted to the magnetic phase diagrams of Nd-substituted Ce 1−x Nd x B 6 [42][43][44].…”

“…Lanthanum doping of CeB 6 suppresses both AFM and AFQ phases and induces a new multipolar-ordered phase IV beyond a quantum critical point (QCP) at x ≈ 0.3, presumably of octupolar character [57][58][59]. Non-Fermi-liquid behavior has been observed in the vicinity of the QCP [60], and a recent specific-heat investigation of substituted Ce 1−x La x B 6 emphasizes the importance of multipolar fluctuations that are directly linked to the effective mass of charge carriers [61]. However, the nature of the ordered multipoles in phase IV, as well as the underlying interactions [62][63][64][65][66], are still a matter of debate.…”

Multipolar order and excitations in rare-earth boride Kondo systems

“…Thus Ce 1−x La x B 6 is one of the few confirmed cases of primary higher rank r ≥ 3 multipolar order. The octupolar order in Ce 1−x La x B 6 persists down to almost x ≈ 0.5 [84]. For even lower x the compounds are disordered at all temperature in zero fields and exhibit a Kondo impurity behavior.…”

“…An example of the global low-field phase diagram of Ce 1−x La x B 6 (x = 0.23) as obtained from magnetocaloric investigations [84] is shown in Fig. 1.13 together with the x-T phase diagram [85].…”