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[en] The Sm M/sub 4,5/ fluorescent emission and characteristic isochromat spectra of Sm metal and SmB6 were measured to obtain information on the valence mixing of SmB6. It was found that the fluorescent spectra do not exhibit resonant emission, which had been observed in the electron-excited spectra measured with relatively low electron-beam energy. The fluorescent spectrum of SmB6 is quite similar to that of Sm metal and the fluorescent and characteristic isochromat spectra of SmB6 show no distinct indication of the spectrum corresponding to the Sm/sup 2+/ ion. The characteristic isochromat spectra at the photon energy of the resonant peak of these materials show that an electron-beam energy beyond 1085 eV is required for the generation of the resonant emission (3d/sub 5/2//sup -1/4f/sup n+1/→3d/sup 10/4f /sup n/), where n is equal to 5 for the Sm/sup 3+/ ion. This is ascribed to the formation of the transient state 3d94f/sup n+2/, which is caused by both the electron excited from the 3d level and the incident electron losing the initial energy. The possibility of a valence change from divalent to trivalent is discussed as the reason no distinct indication of the spectrum corresponding to the Sm/sup 2+/ ion in SmB6 is observed
[en] Resistivity measurements under uniaxial stress have been performed on the intermediate valence compound SmB6 for various directions of the crystal. The experimental technique allows us to explore a limited pressure area (basically 0-3kbar). Nevertheless, the results clearly show an anisotropy; indeed, the effect of the stress in the decrease of the residual resistivity is much higher in the <111> direction than in the <100> and the <110> orientations. This change is witness to the gap anisotropy which must be linked to the theory of excitonic semiconductors
[en] In recent years, studying the Kondo insulator SmB6, a strongly correlated electron material that has been puzzling the community for decades, has again become an attractive topic due to the discovery of its unusual metallic surface state coexisting with the bulk insulating state. Many efforts have been made to understand the microphysics in SmB6, but some puzzles that have been hotly debated and argued have not been solved. In this article, based on the latest progress made in our high-pressure studies on SmB6 and the accumulating results reported by other groups, we propose a notion named the ‘accompany-type valence fluctuation state’, which possibly coexists with the bulk Kondo insulating ground state of SmB6. We expect that this notion could be taken as a common starting point for understanding in a unified way most of the low-temperature phenomena observed by different experimental investigations on SmB6, thus promoting the deciphering of the puzzles. We also expect that this notion could attract rigorous theoretical interpretation and further experimental investigation, or stimulate better thinking on the physics in SmB6. (key issues review)
[en] The prediction that Kondo insulators could be topologically non-trivial renewed interest in SmB6, a material that already earned a reputation as the first mixed valence system and Kondo insulator. Dzero et al.'s proposal connects two of the most topical fields in solid state research: Topological insulators and strongly correlated materials. In addition, robust surface conductivity - inherent to a topological insulator - would elegantly explain SmB6's anomalous transport properties. The notion that samarium hexaboride is a topological Kondo insulator is seemingly confirmed by recent experiments: It is found to be a surface-only conductor at low temperature and surface states have been found at the expected locations. In this talk we will present crucial new insights from high-resolution angle-resolved photoemission spectroscopy  and discuss the implications.
[en] Topological Kondo insulator SmB6 has attracted quite a lot of attention from the condensed matter physics community. A number of unique electronic properties, including low-temperature resistivity anomaly, 1D electronic transport and 2D Fermi surfaces have been observed in SmB6. Here, we report on thermoelectric transport properties of polycrystalline SmB6 over a broad temperature from 300 to 2 K. An anomalous transition in the temperature-dependent Seebeck coefficient S from S(T) T −1 to S(T) T was observed around 12 K. Such a transition demonstrates a transition of conductivity from 3D metallic bulk states to 2D metallic surface states with insulating bulk states. Our results suggest that the thermotransport measurements could be used for the characterization of state transition in topological insulators. (paper)
[en] We have investigated the low temperature conducting state of two Kondo insulators, SmB6 and Ce3Bi4Pt3, which have been theoretically predicted to host topological surface states. Through comparison of the speci c heat of as-grown and powdered single crystals of SmB6, we show that the residual term that is linear in temperature is not dominated by any surface state contribution, but rather is a bulk property. In Ce3Bi4Pt3, we find that the Hall coefficient is independent of sample thickness, which indicates that conduction at low temperatures is dominated by the bulk of the sample, and not by a surface state. The low temperature resistivity of Ce3Bi4Pt3 is found to monotonically decrease with low concentrations of disorder introduced through ion-irradiation. This is in contrast to SmB6, which is again indicative of the contrasting origins of the low temperature conduction. In SmB6, we also show that the effect of low concentrations of irradiation damage of the surface with Fe+ ions is qualitatively consistent with damage with non-magnetic ions.
[en] Conditions of formation and existence of isostructural SmB6 and SmxB6 phases, as well as defect phase stability were determined. Effect of conditions of synthesis, heat treatment (annealing, quenching) on phase composition of nonstoichiometric samarium hexaboride was investigated. Conclusion about possibility of eutectoid decomposition in Sm-B system was made
[en] The structure of SmB4 is determined. The SmB4 monocrystal was an object of investigation. It is shown that while going from Sm to Er distances between boron atoms continuously descrease, i.e. the frame of boron atoms becomes more rigid. It indicates strengthening of the structure of rare earth tetraborides with the increase of serial number of a rare earth atom
[en] XPS 4f spectra of rare-earth hexaborides are presented. Unusually large 4f lifetime broadening was detected throughout the whole series. Its origin is discussed. Of special interest is SmB6, a well-known mixed-valence compound. The Sm 4f spectrum yields several quantitative conclusions regarding the mixed configuration ground state