The lower symmetry electron-density distribution and the charge transport anisotropy in cubic dodecaboride LuB₁₂

Abstract

High-quality single crystals of LuB are grown using the induction zone melting method. The x-ray data are collected at temperatures 293, 135, 95, 50 K. The crystal structure of LuB can be refined with record low R-factor in the cubic Fm [Formula: see text] m symmetry group despite reiterated observations of the cubic symmetry distortions both in the unit-cell values and in the physical properties. A peculiar computing strategy is developed to resolve this contradiction. True symmetry of the electron-density distribution in LuB is proved to be much lower than cubic as a result, which correlates very accurately with anisotropy of transport properties of LuB.

Crystal structures of dodecaborides: complexity in simplicity

“…3.6. These findings are in excellent agreement with the recent experimental results on LuB 12 , which reveal lowersymmetry electron density distribution (charge stripes) correlating with the filamentary structure of conduction channels observed in the magnetoresistance measurements [33]. Remarkably, the general character of the residual density distribution near the metal atom in the (100) and (010) planes at low temperatures (50 K) shown in Fig.…”

“…(2) The JT model provides a physically transparent insight into the origin of lower symmetry electron density distribution in RB 12 , including appearance of charge stripes in LuB 12 and the filamentary structure of conduction channels resulting in anisotropic magnetoresistance [33]. These effects are mainly due to enhanced electron occupation of the 5d z 2 metal orbitals resulting from the larger 5d(R)-2p(B) orbital overlap caused by elastic shortening in the (111) plane in the ferrodistortive JT state (Figs.…”

Local origin of the strong field-space anisotropy in the magnetic phase diagrams of Ce1−xLaxB6 measured in a rotating magnetic field

“…5 the uncertainty of the measurements, as expected in the cubic symmetry. There are known examples among cubic systems where magnetic or transport properties violate the lattice symmetry, for instance due to an anisotropic distribution of lattice defects during crystallization [75] or weak structural distortions [18,76]. Apparently, CeB 6 does not suffer from such complications, so that the cubic symmetry of the magnetization holds to a good approximation.…”

“…Still, even in systems with strong spin-orbit coupling (such as heavy-fermion systems with f electrons), experimentalists commonly do not anticipate either a strong dependence of the system's magnetic properties on the direction of the applied magnetic field or any qualitative change in the magnetic ground-state configuration upon field rotation. Observations of strong field-directional anisotropy in magnetization, specific heat, or magnetotransport data are sometimes interpreted as evidence for spontaneously broken cubic symmetry (e.g., due to the formation of charge stripes [11][12][13][14][15][16][17][18] or electron-nematic instabilities [19,20]) even without quantitative estimates of the expected magnitude of the same effect in the original cubic symmetry of the lattice. In the present work, we provide such an estimate by calculating the field-angular anisotropy of the CEF ground state for a minimal two-site model consisting of a pair of RE ions in a cubic crystal field, coupled by a single exchange interaction.…”

Crystal-field potential and short-range order effects in inelastic neutron scattering, magnetization, and heat capacity of the cage-glass compound HoB12

“…In recent studies of the charge transport, magnetic and thermal properties and fine details of fcc crystal structure of non-magnetic LuB 12 , antiferromagnetic HoB 12 -TmB 12 compounds and solid solutions Tm 1-x Yb x B 12 , it was established that the cooperative Jahn-Teller dynamics of B 12 clusters should be considered as one of the main factors responsible for a strong renormalization of the quasiparticle spectra, electron phase separation and the symmetry breaking in RE dodecaborides [14][15][16][17][18]. It was suggested that the ferrodistortive effect in the boron sublattice generates both collective modes (overdamped oscillators in the frequency range 250-1000 cm -1 [17][18] in the dynamic conductivity spectra of each of the metallic RB 12 compounds and rattling modes, -quasi-local vibrations of heavy rare earth ions embedded in the oversized B 24 cavities.…”