Abstract
The underscreened Kondo lattice consisting of a single twofold degenerate conduction band and a CEF split 4f-electron quasi-quartet has non-conventional quasiparticle dispersions obtained from the constrained mean-field theory. An additional genuinely heavy band is found in the main hybridization band gap of the upper and lower hybridzed bands whose heavy effective mass is controlled by the CEF splitting. Its presence should profoundly influence the dynamical optical and magnetic response functions. In the former, the onset of the optical conductivity is not the main hybridisation energy but the much lower Kondo energy scale which appears in the direct transitions to the additional heavy band. The dynamical magnetic response is also strongly modified by the in-gap heavy band which can lead to unconventional resonant excitations that may be interpreted as coherent CEF-Kondo lattice magnetic exciton bands. Their instability at low temperature signifies the onset of induced excitonic magnetism in the underscreened Kondo lattice.
Highlights
Fundamental electronic properties of correlated f -electron compounds can be qualitatively understood within the Anderson-lattice or Kondo-lattice (KL) models [1,2,3,4,5]
The underscreened Kondo lattice consisting of a single twofold degenerate conduction band and a crystalline electric-field (CEF) split 4 f -electron quasiquartet has nonconventional quasiparticle dispersions obtained from the constrained mean-field theory
An additional genuinely heavy band is found in the main hybridization band gap of the upper and lower hybridzed bands whose heavy effective mass is controled by the CEF splitting
Summary
Fundamental electronic properties of correlated f -electron compounds can be qualitatively understood within the Anderson-lattice or Kondo-lattice (KL) models [1,2,3,4,5]. The STM-QPI (quasiparticle interference) technique has given indications in two heavyfermion metals that the hybridized band structures are more complex than suggested by the common SU(N) KL model with only upper and lower hybridized branches [30,31,32] It is the main purpose of the present work to study in detail inelastic low-energy response of the underscreened quasiquartet KL model based on the results of the previous work [23] to predict the signatures of the additional heavy band of this model in optical conductivity σ (ω) and inelastic neutron scattering S(q, ω). We give a qualitative discussion for the appearance of induced excitonic magnetism due to dominating nondiagonal exchange in the quasiquartet and how the corresponding instability criterion is influenced by the Kondo screening for CEF split f electrons
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