Low temperature magneto-transport of epitaxial samarium hexaboride films

The interplay between localized magnetic magnetic moments and itinerant electrons is at the core of a wide-range of phenomena from the Kondo effect to heavy-fermion behavior. A particular instance of this occurs in samarium hexaboride (SmB₆), where the localized f-moments lie energetically close to a dispersing d-band. The resulting f-d hybridization leads to an insulating state, dubbed a Kondo insulator. Moreover, due to band-inversion between the f-d bands, SmB₆ has been proposed to be a topological Kondo insulator hosting Dirac surface states. Though measurements of bulk SmB₆ crystals have shown agreement with this picture, similar efforts on thin-films have yielded mixed results due to issues with film growth. Hence, optimization of growth recipes and an identification of quantifiable metrics that signify the quality of films is crucial for progress.

In this work, we work with SmB₆ films epitaxially grown on Si by molecular-beam epitaxy and perform magneto-transport with film thickness from 10 to 80 nm. Measurements are performed on unpatterned films via the van der Pauw method and through micro-fabricated Hall bars etched via Ar ion-milling. Hall measurements at 1.5 K suggest a sheet carrier density on the order of 1E16 cm^-2, with parallel conduction, presumably from bulk carriers, freezing out below 10 K. A critical analysis of sheet resistance as a function of film thickness indicates some challenges with growth on Si and points towards strategies that can lead to further optimization of such films.