# Additional energy scale in SmB$_6$ at low temperature

## TL;DR

This study uses low-temperature scanning tunneling microscopy and spectroscopy to reveal complex electronic states in SmB$_6$, shedding light on its topological surface states and the breakdown of the Kondo effect at low temperatures.

## Contribution

It provides detailed spectroscopic evidence of surface and bulk states in SmB$_6$, clarifying its electronic structure and the temperature-dependent Kondo breakdown.

## Key findings

- Surface states develop strongly below 7 K
- Hybridization gap of about 20 meV observed
- Evidence of Kondo effect breakdown at the surface

## Abstract

Topological insulators give rise to exquisite electronic properties due to their spin-momentum locked Dirac-cone-like band structure. Recently, it has been suggested that the required opposite parities between valence and conduction band along with strong spin-orbit coupling can be realized in correlated materials. Particularly, SmB$_6$ has been proposed as candidate material for a topological Kondo insulator. By utilizing scanning tunneling microscopy and spectroscopy measurements down to 0.35 K, we observed several states within the hybridization gap of about $\pm$20 meV on well characterized (001) surfaces of SmB$_6$. The spectroscopic response to impurities and magnetic fields allows to distinguish between dominating bulk and surface contributions to these states. The surface contributions develop particularly strongly below about 7 K which can be understood in terms of a breakdown of the Kondo effect at the surface. Our high-resolution data provide detailed insight into the electronic structure of SmB$_6$, which will reconcile many current discrepancies on this compound.