We report a systematic study of the rhenium-based borides, ReB 2 , Re 7 B 3 , and Re 3 B, by means of the 11 B nuclear magnetic resonance ͑NMR͒ spectroscopy. While Re 7 B 3 and Re 3 B are superconductors, ReB 2 exhibits no superconducting signature but is of current interest due to its superhard mechanical property. Since the major focus of this investigation is their electronic characteristics in the normal states, we performed the measurements at temperatures between 77 and 295 K. For Re 7 B 3 and Re 3 B, s-character electrons were found to be responsible for the observed 11 B NMR Knight shift and spin-lattice relaxation rate ͑1 / T 1 ͒. From T 1 analysis, we thus deduce the partial B s Fermi-level density of states ͑DOS͒ of both borides. On the other hand, the relaxation rate of ReB 2 is mainly associated with p electrons, similar to the cases of OsB 2 and RuB 2 . In addition, the extracted B 2p Fermi-level DOS is in good agreement with the theoretical prediction from band-structure calculations.
We report a 93 Nb nuclear magnetic resonance (NMR) study on the noncentrosymmetric superconductor Re 24 Nb 5. Below the superconducting temperature T c (H), the spin susceptibility probed by the 93 Nb NMR Knight shift gradually decreases with lowering temperature, accompanied by the broadening of the resonance spectrum. Such behavior is commonly observed in the BCS-type superconductors. The 93 Nb NMR spin-lattice relaxation rate (1/T 1) shows a well-defined coherence peak just below T c (H), followed by a marked decrease with further decreasing temperature. Moreover, the 1/T 1 data in the superconducting state were found to obey a single exponential expression, yielding a nodeless gap /k B = 10.3 K. This value gives the ratio of 2 /k B T c (H) = 3.55, that is almost identical with the value of 3.5 predicted from BCS theory. On these bases, we conclude that the noncentrosymmetric Re 24 Nb 5 compound can be characterized as a weakly coupled BCS-type superconductor.
We have investigated the coupled structural and electronic phase transition in the rare-earth ternary silicide Lu 2 Ir 3 Si 5 by means of electrical resistivity ͑͒, Seebeck coefficient ͑S͒, as well as thermal conductivity ͑͒ measurements. Near the phase transition, pronounced anomalies in these transport properties with a significantly large hysteresis of about 40 K were noticed. By comparing the transition characteristics with the earlier reported charge-density-wave ͑CDW͒ systems R 5 Ir 4 Si 10 ͑R = rare-earth elements͒, our present investigation infers the possibility for the CDW transition accompanying a structural transition in this compound. In addition, possible mechanisms for the observed thermal hysteresis have also been proposed.
With the aim of providing experimental information for the correlation between p-d hybridization and phase stability in the D0 22 structure, we performed a comparative investigation on NbAl 3 and NbGa 3 using 93 Nb NMR spectroscopy. The quadrupole splittings, Knight shifts, and spin-lattice relaxation times ͑T 1 's͒ for each individual compound have been identified. The larger quadrupole interaction and higher anisotropic Knight shift have been observed in NbAl 3 , indicative of the stronger hybridization effect for this material, as compared with its isostructural compound NbGa 3 . Results of experimental T 1 together with theoretical band structure calculations provide a measure of d-character Fermi-level density of states N d ͑E F ͒ and an indication of orbital weights. In addition, we found evidence that N d ͑E F ͒ correlates with the structural stability of the studied materials. Our NMR measurements confirm that NbAl 3 is more stable than NbGa 3 with respect to the D0 22 structure, attributed to the stronger p-d hybridization in the former material.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.