Heavy fermion $\textit{d-f}$ hybrid and the SmB$_6$ low temperature phase

TL;DR

This paper models a heavy fermion $d-f$ hybrid system to explain low-temperature properties of SmB$_6$, including specific heat, resistance saturation, and optical conductivity features.

Contribution

It introduces a theoretical model of heavy fermion $d-f$ hybridization that accounts for experimental observations in SmB$_6$ without opening a true insulating gap.

Findings

Qualitative explanation of low-temperature SmB$_6$ properties

Optical conductivity shows a broadened peak at twice the hybridization

Model reproduces linear specific heat and resistance saturation

Abstract

In this Letter we theoretically study physical properties of a model of heavy fermion $d-f$ hybrid. In the studied model two species of fermions have dispersions with different masses, one being much heavier than the other. Hybridization between the fermions at the crossing point of their dispersions doesn't open a true insulating gap leaving a heavy fermion $d-f$ hybrid at the Fermi level. As a result, our theoretical model qualitatively explains experiments on the low-temperature phase of the SmB$_6$. These are the linear in temperature specific heat, saturation of the resistance, and frequency dependence of the optical conductivity. Calculated optical conductivity shows a broadened peak at the twice the value of hybridization as well as a low-frequency tail.