On the Chemistry and Physical Properties of Flux and Floating Zone Grown SmB6 Single Crystals.

Recent theoretical and experimental findings suggest the long-known but not well understood low temperature resistance plateau of SmB6 may originate from protected surface states arising from a topologically non-trivial bulk band structure having strong Kondo hybridization. Yet others have ascribed this feature to impurities, vacancies, and surface reconstructions. Given the typical methods used to prepare SmB6 single crystals, flux and floating-zone procedures, such ascriptions should not be taken lightly. We demonstrate how compositional variations and/or observable amounts of impurities in SmB6 crystals grown using both procedures affect the physical properties. From X-ray diffraction, neutron diffraction, and X-ray computed tomography experiments we observe that natural isotope containing (SmB6) and doubly isotope enriched ((154)Sm(11)B6) crystals prepared using aluminum flux contain co-crystallized, epitaxial aluminum. Further, a large, nearly stoichiometric crystal of SmB6 was successfully grown using the float-zone technique; upon continuing the zone melting, samarium vacancies were introduced. These samarium vacancies drastically alter the resistance and plateauing magnitude of the low temperature resistance compared to stoichiometric SmB6. These results highlight that impurities and compositional variations, even at low concentrations, must be considered when collecting/analyzing physical property data of SmB6. Finally, a more accurate samarium-154 coherent neutron scattering length, 8.9(1) fm, is reported.

Crystal growth, structure, and physical properties of Ln(Ag, Al, Si)2 (Ln = Ce and Gd).

Single crystals of CeM2 and GdM2 (M = Ag, Al, and Si) were grown by the flux growth technique and characterized by means of single crystal x-ray diffraction, magnetic susceptibility, resistivity, and heat capacity measurements. CeM2 and GdM2 crystallize in the tetragonal I4(1)/amd space group with the α-ThSi2 structure type with lattice parameters a ~4.2 Å and c ~14.4 Å. Curie-Weiss behavior is observed for both analogues with CeM2 ordering first ferromagnetically at 11 K with a second antiferromagnetic transition at 8.8 K while GdM2 orders antiferromagnetically at 24 K. Heat capacity measurements on CeM2 show two magnetic transitions at 10.8 and 8.8 K with an electronic specific heat coefficient, γ(0), of ~53 mJ K(-2) mol(-1). The entropy at the magnetic transition is less than the expected Rln2 for CeM2, reinforcing the assertions of an enhanced mass state and Kondo behavior being observed in the resistivity.