Study of the Role of Disorder in SmB₆ with Samarium Vacancies and Alloys of SmB₆

Samarium Hexaboride (SmB₆) is a unique strongly correlated electron material that hosts topologically protected surface states and a truly insulating bulk. With our newly developed inverted resistance measurement method, we were able to obtain bulk transport data below the temperature wherein surface conductivity becomes dominant. Through this data we find strong evidence that the bulk is immune to disorder due to identical activation energies in samples with varying vacancies. At temperatures below 2.5 K, however, there is a plateau present which functions almost independent of temperature and whose magnitude seems dependent on the amount of samarium vacancies present in the sample. We hypothesize that some form of extended defects may be responsible for this behavior. We have characterized the crystals using X-ray diffraction, Auger, high-resolution TEM, energy dispersive X-ray spectroscopy, and Vicker’s hardness measurements. With increasing vacancy concentration, we found a significant reduction in the hardness of SmB₆ crystals and direct evidence for twinning in X-ray studies, confirming the presence of extended defects.