Importance of orbital fluctuations for the magnetic dynamics in heavy-fermion compound SmB$_6$

TL;DR

This study explores how orbital fluctuations influence magnetic excitations in the heavy-fermion compound SmB$_6$, revealing a complex interplay that affects its quantum critical behavior and matches experimental observations.

Contribution

It demonstrates the importance of orbital fluctuations in magnetic dynamics of SmB$_6$ using a multiorbital first-principles approach combined with RPA analysis.

Findings

Spin and orbital fluctuations are highly interconnected in SmB$_6$.

The magnetic phase diagram shows quantum critical features with multiple competing phases.

Low energy spin excitations are linked with orbital fluctuations, indicating entanglement.

Abstract

The emergent dynamical processes associated with magnetic excitations in heavy-fermion SmB$_6$ are investigated. By imposing multiorbital interactions on a first-principles model, we find the interplay between spin and orbital fluctuations in the $f$ manifold is highly sensitive to local correlations. The magnetic phase diagram constructed at zero temperature reveals quantum critical features with the existence of several competing phases. Within the random phase approximation, we perform a comprehensive study of the spin-spin correlation function, and our results agree with neutron scattering experiments. Spectral weight analysis shows the low energy spin excitations are selectively accompanied by orbital fluctuations, indicating a non-trivial entanglement between the spin and orbital degree of freedom driven by relativistic couplings.