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

TL;DR

This study investigates how compositional variations and impurities in SmB6 crystals grown by flux and floating zone methods influence their physical properties, emphasizing the importance of sample purity in understanding their low-temperature resistance behavior.

Contribution

It provides detailed analysis of impurity phases and vacancies in SmB6 crystals grown by different methods, and reports a new neutron scattering length for samarium-154.

Findings

Impurity phases like aluminum can co-crystallize in flux-grown SmB6.

Samarium vacancies introduced during float-zone growth significantly affect resistance.

A new neutron scattering length for samarium-154 is reported.

Abstract

Recent theoretical and experimental findings suggest that 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 other studies have ascribed this feature to impurity phases, sample vacancies, and surface reconstructions. Given the typical methods used to prepare SmB6 single crystals, the flux and floating zone procedures, these ascriptions should not be taken lightly. Here, we demonstrate how compositional variations and observable amounts of impurity phases in SmB6 crystals grown by floating zone and flux affect the physical properties. From neutron diffraction and X-ray computed tomography experiments, we observe that a 154Sm11B6 crystal prepared using aluminum flux contains co-crystallized, epitaxial aluminum. A large, nearly stoichiometric crystal of SmB6 was successfully grown using the float-zone technique; upon continuing the zone melting, samarium vacancies are introduced. These samarium vacancies drastically alter the resistance and plateauing magnitude of the low temperature resistance compared to stoichiometric SmB6. These results highlight that small presences of impurity phases and compositional variations must be considered when collecting and analyzing physical property data of SmB6. Finally, a more accurate samarium-154 coherent neutron scattering length value, 8.9(1) fm, is reported.