Persistence of correlation-driven surface states in SmB6 under pressure

TL;DR

This study investigates how pressure affects the surface states of SmB6, revealing that correlation-driven surface states persist and their effective mass increases with pressure, supporting the presence of a surface Kondo effect.

Contribution

It provides experimental evidence that the correlation-driven surface states in SmB6 persist under pressure and their effective mass increases, indicating a robust surface Kondo effect.

Findings

Surface carrier density increases with pressure.

Fermi energy remains unchanged under pressure.

Surface effective mass increases linearly with pressure.

Abstract

The proposed topological Kondo insulator SmB$_{6}$ hosts a bulk Kondo hybridization gap that stems from strong electronic correlations and a metallic surface state whose effective mass remains disputed. Thermopower and scanning tunneling spectroscopy measurements argue for heavy surface states that also stem from strong correlations, whereas quantum oscillation and angle-resolved photoemission measurements reveal light effective masses that would be consistent with a Kondo breakdown scenario at the surface. Here we investigate the evolution of the surface state via electrical and thermoelectric transport measurements under hydrostatic pressure, a clean symmetry-preserving tuning parameter that suppresses the Kondo gap and increases the valence of Sm from 2.6+ towards a 3+ magnetic metallic state. Electrical resistivity measurements reveal that the surface carrier density increases with increasing pressure, whereas thermopower measurements show an unchanged Fermi energy under pressure. As a result, the effective mass of the surface state charge carriers linearly increases with pressure as the Sm valence approaches 3+. Our results are consistent with the presence of correlation-driven surface states in SmB$_{6}$ and suggest that the surface Kondo effect persists under pressure to 2 GPa.