Meta-orbital Transition in Heavy-fermion Systems: Analysis by Dynamical Mean Field Theory and Self-consistent Renormalization Theory of Orbital Fluctuations

TL;DR

This paper explores a meta-orbital transition in heavy-fermion systems using dynamical mean field theory and renormalization techniques, revealing critical orbital fluctuations relevant to certain Ce-based compounds.

Contribution

It introduces a combined DMFT and self-consistent renormalization approach to analyze meta-orbital transitions and fluctuations in heavy-fermion systems, highlighting the role of orbital hybridization.

Findings

Meta-orbital transition occurs with steep orbital occupancy change.

Orbital fluctuations are enhanced near the critical end point.

Coupling between orbital and charge fluctuations is significant.

Abstract

We investigate a two-orbital Anderson lattice model with Ising orbital intersite exchange interactions by means of dynamical mean field theory combined with the static mean field approximation of the intersite orbital interactions. Focusing on Ce-based heavy-fermion compounds, we examine the orbital crossover between the two orbital states, when the total f-electron number per site n_f is n_f ~ 1. We show that a "meta-orbital" transition, at which the occupancy of the two orbitals changes steeply, occurs when the hybridization between the ground-state f-electron orbital and conduction electrons are smaller than that between the excited f-electron orbital and conduction electrons. Near the meta-orbital critical end point, the orbital fluctuations are enhanced, and couple with the charge fluctuations. A critical theory of the meta-orbital fluctuations is also developed by applying the self-consistent renormalization theory of itinerant electron magnetism to the orbital fluctuations. The critical end point, first-order transition and crossover are described within Gaussian approximations of orbital fluctuations. We discuss the relevance of our results to CeAl2, CeCu2Si2, CeCu2Ge2 and the related compounds, which all have low-lying crystalline-electric-field excited states.