Composition-spread Growth and the Robust Topological Surface State of Kondo insulator SmB6 Thin Films

TL;DR

This study demonstrates the growth of smooth SmB6 thin films with robust topological surface states, showing insulating bulk behavior and surface conduction, confirmed through transport measurements and spectroscopy.

Contribution

First fabrication of smooth nanocrystalline SmB6 thin films exhibiting topological surface states with transport and spectroscopic evidence of their robustness.

Findings

Resistivity increases below 50 K due to hybridization gap formation

Resistivity saturates below 10 K indicating surface conduction

Spectroscopy reveals coexistence of Kondo lattice and metallic surface states

Abstract

Topological insulators are a class of materials with insulating bulk but protected conducting surfaces due to the combination of spin-orbit interactions and time-reversal symmetry. The surface states are topologically non-trivial and robust against non-magnetic backscattering, leading to interesting physics and potential quantum computing applications1, 2. Recently there has been a fast growing interest in samarium hexboride (SmB6), a Kondo insulator predicted to be the first example of a correlated topological insulator3, 4. Here we fabricated smooth thin films of nanocrystalline SmB6 films. Their transport behavior indeed shows that SmB6 is a bulk insulator with topological surface states. Upon decreasing the temperature, the resistivity \r{ho} of Sm0.14B0.86 (SmB6) films display significant increase below 50 K due to hybridization gap formation, and it shows a saturation behavior below 10 K. The saturated resistance of our textured films is similar to that of the single crystals, suggesting that this conduction is from the surface and robust against grain boundary scatterings. Point contact spectroscopy (PCS) of the film using a superconducting tip displays both a Kondo Fano resonance and Andreev reflection, suggesting the existence of both an insulating Kondo lattice and metallic surface states.