Bulk transport paths through defects in floating zone and Al flux grown SmB$_6$

TL;DR

This study examines how different crystal growth methods affect low-temperature bulk and surface conduction in SmB$_6$, highlighting the role of dislocations and defects in residual bulk conduction.

Contribution

It provides new insights into the impact of growth-induced defects, especially dislocations, on the transport properties of SmB$_6$ crystals from different synthesis methods.

Findings

Residual bulk conduction varies significantly between growth methods.

Dislocations are more prevalent in floating zone samples and may contribute to conduction.

Hopping in impurity bands alone cannot explain the observed bulk conduction.

Abstract

We investigate the roles of disorder on low-temperature transport in SmB$_6$ crystals grown by both the Al flux and floating zone methods. We used the inverted resistance method with Corbino geometry to investigate whether low-temperature variations in the standard resistance plateau arises from a surface or a bulk channel in floating zone samples. The results show significant sample-dependent residual bulk conduction, in contrast to smaller amounts of residual bulk conduction previously observed in Al flux grown samples with Sm vacancies. We consider hopping in an activated impurity band as a possible source for the observed bulk conduction, but it is unlikely that the large residual bulk conduction seen in floating zone samples is solely due to Sm vacancies. We therefore propose that one-dimensional defects, or dislocations, contribute as well. Using chemical etching, we find evidence for dislocations in both flux and floating zone samples, with higher dislocation density in floating zone samples than in Al flux grown samples. In addition to the possibility of transport through one-dimensional dislocations, we also discuss our results in the context of recent theoretical models of SmB$_6$.