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Register a new userEffect of Nd and Rh substitution on the spin dynamics of Kondo insulator CeFe2Al10
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The dynamic magnetic properties of the Kondo-insulator state in CeFe2Al10 (spin gap, resonance mode) have been investigated using polarized neutrons on a single crystal of pure CeFe2Al10. The results indicate that the magnetic excitations are polarized mainly along the orthorhombic a axis and their dispersion along the orthorhombic c direction could be determined. Polycrystalline samples of Nd- and Rh-doped CeFe2Al0 were also studied by the time-of-flight technique, with the aim of finding out how the low-energy magnetic excitation spectra change upon isoelectronic substitution of the rare-earth (Nd) on the magnetic Ce site or electron doping (Rh) on the transition-element Fe sublattice. The introduction of magnetic Nd impurities strongly modifies the spin gap in the Ce dynamic magnetic response and causes the appearance of a quasielastic signal. The crystal-field excitations of Nd, studied in both LaFe2Al10 and CeFe2Al10, also reveal a significant influence of f-electron hybridization (largest in the case of Ce) on the crystal-field potential. As a function of the Rh concentration, a gradual change is observed from a Kondo-insulator to a metallic Kondo-lattice response, likely reflecting the decrease in the hybridization energy.
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Neutron powder diffraction measurements have been performed on Ce_xNd_{1-x}B_6 (x = 0.5, 0.6, 0.7, and 0.8) solid solutions to determine the type of magnetic order occurring in these compounds as a result of the interplay between magnetic dipole exchange and antiferroquadrupolar interactions. In the Ce-rich range, the sequence of two magnetic phases, with an incommensurate order [k = (1/4 -delta, 1/4 -delta, 1/2)] forming below T N followed by a lock-in--type transition at lower temperature, is quite similar to that reported earlier for Ce_xPr_{1-x} B_6. For x = 0.5, on the other hand, the same antiferromagnetic order as in pure NdB6 first occurs at TN, then coexists with an incommensurate component below the lower transition temperature. These results are in good agreement with previous resistivity measurements and support the idea that Ce and Nd magnetic moments in this system can be relatively decoupled.
A synergistic effect between strong electron correlation and spin-orbit interaction (SOI) has been theoretically predicted to result in a new topological state of quantum matter on Kondo insulators (KIs), so-called topological Kondo insulators (TKIs). One TKI candidate has been experimentally observed on the KI SmB6(001), and the origin of the surface states (SS) and the topological order of SmB6 has been actively discussed. Here, we show a metallic SS on the clean surface of another TKI candidate YbB12(001), using angle-resolved photoelectron spectroscopy. The SS showed temperature-dependent reconstruction corresponding with the Kondo effect observed for bulk states. Despite the low-temperature insulating bulk, the reconstructed SS with c-f hybridization was metallic, forming a closed Fermi contour surrounding $bar{Gamma}$ on the surface Brillouin zone and agreeing with the theoretically expected behavior for SS on TKIs. These results demonstrate the temperature-dependent holistic reconstruction of two-dimensional states localized on KIs surface driven by the Kondo effect.
The CeT2Al10 family of orthorhombic compounds exhibits a very peculiar evolution from a Kondo-insulator (T: Fe) to an unconventional long-range magnetic order (T: Ru, Os). Inelastic neutron scattering experiments performed on single-crystal CeFe2Al10 reveal that this material develops a spin-gap in its magnetic spectral response below ~ 50 K, with a magnetic excitation dispersing from $E = 10.2 pm 0.5$ meV at the Y zone-boundary point [q = (0,1,0)] to $approx 12$ meV at the top of the branch. The excitation shows a pronounced polarization of the magnetic fluctuations along a, the easy anisotropy axis. Its behavior is contrasted with that of the (magnonlike) modes previously reported for CeRu2Al10, which have transverse character and exist only in the antiferromagnetic state. The present observation is ascribed to a magnetic exciton mechanism invoked to explain a similar magnetic response previously discovered in YbB12.
We study Kondo physics of a spin-$frac{1}{2}$ impurity in electronic matter with strong spin-orbit interaction, which can be realized by depositing magnetic adatoms on the surface of a three-dimensional topological insulator. We show that magnetic properties of topological surface states and the very existence of Kondo screening strongly depend on details of the bulk material, and specifics of surface preparation encoded in time-reversal preserving boundary conditions for electronic wavefunctions. When this tunable Kondo effect occurs, the impurity spin is screened by purely orbital motion of surface electrons. This mechanism gives rise to a transverse magnetic response of the surface metal, and spin textures that can be used to experimentally probe signatures of a Kondo resonance. Our predictions are particularly relevant for STM measurements in ${rm Pb Te}$-class crystalline topological insulators, but we also discuss implications for other classes of topological materials.
We report temperature-dependent polarized optical conductivity [$sigma(omega)$] spectra of CeFe$_2$Al$_{10}$, which is a reference material for CeRu$_2$Al$_{10}$ and CeOs$_2$Al$_{10}$ with an anomalous magnetic transition at 28 K. The $sigma(omega)$ spectrum along the b-axis differs greatly from that in the $ac$-plane, indicating that this material has an anisotropic electronic structure. At low temperatures, in all axes, a shoulder structure due to the optical transition across the hybridization gap between the conduction band and the localized $4f$ states, namely $c$-$f$ hybridization, appears at 55 meV. However, the gap opening temperature and the temperature of appearance of the quasiparticle Drude weight are strongly anisotropic indicating the anisotropic Kondo temperature. The strong anisotropic nature in both electronic structure and Kondo temperature is considered to be relevant the anomalous magnetic phase transition in CeRu$_2$Al$_{10}$ and CeOs$_2$Al$_{10}$.
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