The Effects of Spin-Excitons on the Surface States of SmB6: A Photoemission Study

TL;DR

This study uses high-resolution photoemission spectroscopy to investigate surface states in SmB6, revealing a spin-exciton resonance that affects surface state protection and low-temperature electronic properties.

Contribution

It provides evidence for spin-exciton effects on surface states in SmB6, linking spectroscopic features to scattering mechanisms that influence surface conductivity.

Findings

Detection of a V-shaped surface density of states within the bulk gap.

Observation of a low-energy feature at -9 meV linked to spin-exciton scattering.

Implication that spin-excitons suppress coherent surface quasiparticles.

Abstract

We present the results of high-resolution valence-band photoemission spectroscopic study of SmB6 which shows evidence for a V-shaped density of states of surface origin within the bulk gap. The spectroscopy data is interpreted in terms of the existence of heavy 4f surface states, which may be useful in resolving the controversy concerning the disparate surface Fermi-surface velocities observed in experiments. Most importantly, we find that the temperature dependence of the valence-band spectrum indicates that a small feature appears at a binding energy of about -9 meV at low temperatures. We attribute this feature to a resonance caused by the spin-exciton scattering in SmB6 which destroys the protection of surface states due to time-reversal invariance and spin-momentum locking. The existence of a low-energy spin-exciton may be responsible for the scattering which suppresses the formation of coherent surface quasi-particles and the appearance of the saturation of the resistivity to temperatures much lower than the coherence temperature associated with the opening of the bulk gap.