Nesting-driven multipolar order in CeB6 from photoemission tomography

Some heavy fermion materials show so-called hidden-order phases which are invisible to many characterization techniques and whose microscopic origin remained controversial for decades. Among such hidden-order compounds, CeB6 is of model character due to its simple electronic configuration and crystal structure. Apart from more conventional antiferromagnetism, it shows an elusive phase at low temperatures, which is commonly associated with multipolar order. Here we show that this phase roots in a Fermi surface instability. This conclusion is based on a full 3D tomographic sampling of the electronic structure by angle-resolved photoemission and comparison with inelastic neutron scattering data. The hidden order is mediated by itinerant electrons. Our measurements will serve as a paradigm for the investigation of hidden-order phases in f-electron systems, but also generally for situations where the itinerant electrons drive orbital or spin order

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

The strongly correlated system Ho11B12 with boron sublattice Jahn Teller instability and nanoscale electronic phase separation dynamic charge stripes was studied in detail by inelastic neutron scattering INS , magnetometry, and heat capacity measurements at temperatures in the range of 3 300 K. From the analysis of registered INS spectra, we determined parameters of the cubic crystal field CF at holmium sites B4 amp; 8722;0.333 meV and B6 amp; 8722;2.003 meV in Stevens notations , with an unconventional large ratio B6 B4 pointing to the dominant role of conduction electrons in the formation of a CF potential. The molecular field in the antiferromagnetic AFM state Bloc 1.75 0.1 T has been directly determined from the INS spectra together with short range order effects detected in the paramagnetic state. A comparison of measured magnetization in diluted Lu0.99Ho0.01B12 and concentrated HoB12 single crystals showed a strong suppression of Ho magnetic moments by AFM exchange interactions in holmium dodecaboride. To account explicitly for the short range AFM correlations, a self consistent holmium dimer model was developed that allowed us to reproduce successfully field and temperature variations of the magnetization and heat capacity in the cage glass phase of HoB12 in external magnetic field

Field-Angle-Resolved Magnetic Excitations as a Probe of Hidden-Order Symmetry in CeB6

In contrast to magnetic order formed by electrons' dipolar moments, ordering phenomena associated with higher-order multipoles (quadrupoles, octupoles, etc.) are more difficult to characterize because of the limited choice of experimental probes that can distinguish different multipolar moments. The heavy-fermion compound CeB6 and its La-diluted alloys are among the best-studied realizations of the long-range-ordered multipolar phases, often referred to as "hidden order."Previously, the hidden order in phase II was identified as primary antiferroquadrupolar and field-induced octupolar order. Here, we present a combined experimental and theoretical investigation of collective excitations in phase II of CeB6. Inelastic neutron scattering (INS) in fields up to 16.5 T reveals a new high-energy mode above 14 T in addition to the low-energy magnetic excitations. The experimental dependence of their energy on the magnitude and angle of the applied magnetic field is compared to the results of a multipolar interaction model. The magnetic excitation spectrum in a rotating field is calculated within a localized approach using the pseudospin representation for the Γ8 states. We show that the rotating-field technique at fixed momentum can complement conventional INS measurements of the dispersion at a constant field and holds great promise for identifying the symmetry of multipolar order parameters and the details of intermultipolar interactions that stabilize hidden-order phases. © 2020 authors. Published by the American Physical Society

Thermionic properties of lutetium borides single crystals

Results of the LuB₁₂ (100), (110), (111), LuB₄ (001), LuB₂ (001) thermionic properties study in the temperature range T = 1200...1960 K at p ≤ 10⁻⁴ Pa pressure are presented. The correlation between structure and composition of the lutetium borides single-crystal samples and their thermionic properties are shown. The electron work function anisotropy of the LuB₁₂ low-index planes are determined by the lutetium and boron atoms reticular density and the electric dipole moment of the unreconstructed (100), (110), (111) planes of the UB₁₂ type lattice structure

Thermionic properties of LaB₆-(Ti₀¸₆Zr₀¸₄)B₂ material

The thermionic emmision peculiarities of filber reinforced boride composite ceramic material LaB₆-(Ti₀¸₆Zr₀¸₄)B₂ produced by directional crystallization of eutectic alloy have been studied. Activation modes, electron work function temperature dependence, poisonin under air leakink have been determined. The obtained data are compared with emission characteristics of (100) LaB₆ single crystal and quasi-binary eutectic materials LaB₆-TiB₂ and LaB₆-ZrB₂

Effect of Zr substitution by Ti on growth direction and interface structure of LaB6-TixZr1−xB2 directionally solidified eutectics

International audienceBoride ceramics were directionally solidified around LaB6-(TixZr1−x)B2 eutectic compositions. The directionally solidified rods were composed of LaB6 rich concentric belts surrounding large eutectic regions with a dense and uniform distribution of (TixZr1−x)B2 fibers of 0.6 μm in diameter inside a LaB6 matrix. The di- and hexa-boride mole fractions at eutectic points have been more accurately defined for x = 0-0.76. Fiber growth directions were modified by the addition of titanium. Diboride (subscript 2) fibers grew along [0 0 0 1]2 for x = 0 and along View the MathML source〈1¯ 1 0 0〉2 for x ≠ 0. The orientation of the hexaboride (subscript 6) matrix was unchanged with or without titanium addition. The favored crystallographic orientation relationship was: [0 0 1]6//[0 0 0 1]2 and View the MathML source(1 1 0)6//(1 1 2¯ 0)2 and View the MathML source(1¯ 1 0)6//(1¯ 1 0 0)2 for any x value. The dominant interfaces were View the MathML source{1 1 0}6//{1 1 2¯ 0}2 for x = 0 and (0 0 1)6//(0 0 0 1)2 for x ≠ 0, the latter being expected to be energetically more favorable, as predicted by a 2D geometrical model

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

The strongly correlated system HoB1211 with boron sublattice Jahn-Teller instability and nanoscale electronic phase separation (dynamic charge stripes) was studied in detail by inelastic neutron scattering (INS), magnetometry, and heat capacity measurements at temperatures in the range of 3-300 K. From the analysis of registered INS spectra, we determined parameters of the cubic crystal field (CF) at holmium sites B4=-0.333 meV and B6=-2.003 meV (in Stevens notations), with an unconventional large ratio B6/B4 pointing to the dominant role of conduction electrons in the formation of a CF potential. The molecular field in the antiferromagnetic (AFM) state Bloc=(1.75±0.1) T has been directly determined from the INS spectra together with short-range order effects detected in the paramagnetic state. A comparison of measured magnetization in diluted Lu0.99Ho0.01B12 and concentrated HoB12 single crystals showed a strong suppression of Ho magnetic moments by AFM exchange interactions in holmium dodecaboride. To account explicitly for the short-range AFM correlations, a self-consistent holmium dimer model was developed that allowed us to reproduce successfully field and temperature variations of the magnetization and heat capacity in the cage-glass phase of HoB12 in external magnetic fields

The Rashba Splitting in SmB6

The present article highlights two aspects at the intersection between Rashba physics and topological matter. Topologically nontrivial matter has been in the focus for almost two decades. It depends strongly on spin orbit coupling but, in contrast to large parts of modern solid state physics, strong electron correlation does not play a major role. In this context, SmB6 has been suggested as the first topological insulator driven by strong electron correlation and the first topological Kondo insulator. We review the important role of the Rashba splitting in determining that the observed surface states are not topological. Moreover, we point out that the Rashba splitting of SmB6 represents the extreme case of a large splitting in momentum space at a small Rashba paramete