Electronic Orders Induced by Kondo Effect in Non-Kramers f-Electron Systems

TL;DR

This paper investigates the microscopic nature of staggered scalar order in non-Kramers f-electron systems, revealing a transition from CEF singlets to Kondo singlets and identifying a new electronic order near the boundary of localized and itinerant states.

Contribution

It introduces a phenomenological three-state model and numerical methods to explain the staggered order and phase diagram in non-Kramers f-electron systems, linking it to experimental observations.

Findings

Identification of staggered Kondo and CEF singlet order

Development of a three-state phenomenological model

Prediction of sharp spectral peaks in ordered phase

Abstract

This paper clarifies the microscopic nature of the staggered scalar order, which is specific to even number of f electrons per site. In such systems, crystalline electric field (CEF) can make a singlet ground state. As exchange interaction with conduction electrons increases, the CEF singlet at each site gives way to Kondo singlets. The collective Kondo singlets are identified with itinerant states that form energy bands. Near the boundary of itinerant and localized states, a new type of electronic order appears with staggered Kondo and CEF singlets. We present a phenomenological three-state model that qualitatively reproduces the characteristic phase diagram, which have been obtained numerically with use of the continuous-time quantum Monte Carlo combined with the dynamical mean-field theory. The scalar order observed in PrFe_4P_{12} is ascribed to this staggered order accompanying charge density wave (CDW) of conduction electrons. Accurate photoemission and tunneling spectroscopy should be able to probe sharp peaks below and above the Fermi level in the ordered phase.