Novel Kondo-like behavior near magnetic instability in SmB$_6$ : temperature and pressure dependences of Sm valence

TL;DR

This study investigates how pressure and temperature influence the valence state of Sm in SmB$_6$, revealing a Kondo-like behavior near magnetic instability and unusual valence shifts at the transition point.

Contribution

It provides the first systematic analysis of Sm valence under varying pressure and temperature, highlighting a novel Kondo-like behavior near magnetic instability in SmB$_6$.

Findings

Pressure induces magnetic order above 10 GPa.

Sm valence shifts toward localized 4f states with pressure and temperature.

Valence at the transition point is anomalously below 3, indicating unusual electronic behavior.

Abstract

We report a systematic study of Sm valence in the prototypical intermediate valence compound SmB$_6$. Sm mean valence, $v_{\rm Sm}$, was measured by X-ray absorption spectroscopy as functions of pressure ($1<P<13$ GPa) and temperature ($3<T<300$ K). Pressure induced magnetic order (MO) was detected above $P_c = 10$ GPa by resistivity measurements. A shift toward localized $4f$ state with increasing $P$ and/or $T$ is evident from an increase in $v_{\rm Sm}$. However $v_{\rm Sm}$ at $P_c$ is anomalously far below 3, which differs from the general case of nonmagnetic-magnetic transition in Yb and Ce compounds. From the $T$ dependence of $v_{\rm Sm}(P,T)$, we found that $v_{\rm Sm}(P,T)$ consists of two different characteristic components: one is associated with low-energy electronic correlations involving Kondo like behavior, and the other with high-energy valence fluctuations.