Chemical and valence reconstruction at the surface of SmB6 revealed with resonant soft x-ray reflectometry

Abstract

Samarium hexaboride (SmB${}_6$), a Kondo insulator with mixed valence, has recently attracted much attention as a possible host for correlated topological surface states. Here, we use a combination of x-ray absorption and reflectometry techniques, backed up with a theoretical model for the resonant $M_{4,5}$ absorption edge of Sm and photoemission data, to establish laterally averaged chemical and valence depth profiles at the surface of SmB${}_6$. We show that upon cleaving, the highly polar (001) surface of SmB${}_6$ undergoes substantial chemical and valence reconstruction, resulting in boron termination and a Sm${}^{3+}$ dominated sub-surface region. Whereas at room temperature, the reconstruction occurs on a time scale of less than two hours, it takes about 24 hours below 50 K. The boron termination is eventually established, irrespective of the initial termination. Our findings reconcile earlier depth resolved photoemission and scanning tunneling spectroscopy studies performed at different temperatures and are important for better control of polarity and, as a consequence, surface states in this system.

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Cited by in corpus (6)

• Observation of a well-defined hybridization gap and in-gap states on the SmB6 (001) surface
• Diamagnetic Sm${}^{3+}$ in the topological Kondo insulator SmB${}_6$
• Topology of SmB${}_6$ determined by dynamical mean field theory
• An STM perspective on hexaborides: Surface states of the Kondo insulator SmB${}_6$
• Local polarization and valence distribution in LaNiO3/LaMnO3 heterostructures
• Surface excitations relaxation in the Kondo insulator Sm${}_{1-x}$Gd${}_x$B${}_6$