Charge fluctuations in the intermediate-valence ground state of SmCoIn$_5$

TL;DR

This study investigates charge fluctuations and valence crossover in SmCoIn$_5$, revealing the importance of crystal field effects and delocalization of $f$ electrons in heavy fermion behavior and quantum criticality.

Contribution

It demonstrates that crystal field effects dominate $f$ electron delocalization in SmCoIn$_5$, highlighting charge fluctuations' role in heavy fermion ground states.

Findings

SmCoIn$_5$ exhibits a $ ext{Gamma}_7$ ground state similar to CeCoIn$_5$

Temperature-induced valence crossover occurs around 60 K

Charge fluctuations are significant in the ground state of 115 materials

Abstract

The microscopic mechanism of heavy band formation, relevant for unconventional superconductivity in CeCoIn$_5$ and other Ce-based heavy fermion materials, depends strongly on the efficiency with which $f$ electrons are delocalized from the rare earth sites and participate in a Kondo lattice. Replacing Ce$^{3+}$ ($4f^1$, $J=5/2$) with Sm$^{3+}$ ($4f^5$, $J=5/2$), we show that a combination of crystal field and on-site Coulomb repulsion causes SmCoIn$_5$ to exhibit a $\Gamma_7$ ground state similar to CeCoIn$_5$ with multiple $f$ electrons. Remarkably, we also find that with this ground state, SmCoIn$_5$ exhibits a temperature-induced valence crossover consistent with a Kondo scenario, leading to increased delocalization of $f$ holes below a temperature scale set by the crystal field, $T_v$ $\approx$ 60 K. Our result provides evidence that in the case of many $f$ electrons, the crystal field remains the most important tuning knob in controlling the efficiency of delocalization near a heavy fermion quantum critical point, and additionally clarifies that charge fluctuations play a general role in the ground state of "115" materials.