Multipolar phases and magnetically hidden order: review of the heavy-fermion compound Ce_1−xLa_xB₆

Abstract

Cerium hexaboride is a cubic f-electron heavy-fermion compound that displays a rich array of low-temperature magnetic ordering phenomena which have been the subject of investigation for more than 50 years. Its complex behaviour is the result of competing interactions, with both itinerant and local electrons playing important roles. Investigating this material has proven to be a substantial challenge, in particular because of the appearance of a 'magnetically hidden order' phase, which remained elusive to neutron-scattering investigations for many years. It was not until the development of modern x-ray scattering techniques that the long suspected multipolar origin of this phase was confirmed. Doping with non-magnetic lanthanum dilutes the magnetic cerium sublattice and reduces the f-electron count, bringing about substantial changes to the ground state with the emergence of new phases and quantum critical phenomena. To this day, Ce1-x La x B6 and its related compounds remain a subject of intense interest. Despite the substantial progress in understanding their behaviour, they continue to reveal new and unexplained physical phenomena. Here we present a review of the accumulated body of knowledge on this family of materials in order to provide a firm standpoint for future investigations.

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

“…A model example of intriguing heavy-fermion physics is CeB 6 , which exhibits a very complex magnetic phase diagram and a rich spectrum of excitations, indicating a delicate balance between different microscopic interactions despite very simple crystal and electronic structures [29][30][31]. Zero-field phase diagram of CeB 6 consists of a complex double-q antiferromagnetic (AFM) phase below T N = 2.3 K [32] and the so-called "hidden order" phase II between T N and T Q = 3.2 K, which results from a G-type antiferroquadrupolar (AFQ) ordering of the x y , yz and z x quadrupolar moments of Ce 3+ ions [33][34][35][36][37].…”

“…Most recently, an additional crossover was found in the behavior of the anisotropic magnetoresistance inside phase II, separating this phase into two regions characterized by opposite signs of the resistance anisotropy with respect to the field direction [38]. In contrast to the spectrum of a conventional antiferromagnet with Goldstone modes stemming [31,[39][40][41][42][43][44][45][46][47] at zero field. Phases II and IV are associated with the two multipolar phases with AFQ and octupolar ordering.…”

“…Phases II and IV are associated with the two multipolar phases with AFQ and octupolar ordering. The "SC" dome at the bottom-right corner schematically indicates the dubious superconducting phase of the pure LaB 6 [31,[48][49][50]. Phases III, V and VI are three different types of AFM ordering, realized in Ce 1−x Nd x B 6 .…”

Magnetic field dependence of the neutron spin resonance inCeB6

“…Cerium hexaboride is a nonsuperconducting heavyfermion metal with a simple-cubic crystal structure [30]. Competition between the Kondo screening and the Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling mechanism via conduction electrons leads to a rich magnetic-fieldtemperature phase diagram.…”

Incommensurate short-range multipolar order parameter of phase II in Ce3Pd20Si6

“…Such hidden-order phases have been observed in a variety of compounds containing 4 f and 5 f elements, for example, URu 2 Si 2 [1,2], NpO 2 [3], skutterudites [4,5], YbRu 2 Ge 2 [6], or CeB 6 [7][8][9]. It is often assumed that the multipolar moments of the f electrons in their specific crystal-field environment play a decisive role in the formation of these phases [10][11][12].…”