Competition between Quadrupole and Magnetic Kondo Effects in Non-Kramers Doublet Systems

Hiroaki Kusunose,Takahiro Onimaru

doi:10.1088/1742-6596/592/1/012099

Hiroaki Kusunose, Takahiro Onimaru

Open Access

https://doi.org/10.1088/1742-6596/592/1/012099

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Abstract

We discuss possible competition between magnetic and quadrupole Kondo effects in non-Kramers doublet systems in cubic symmetry. The quadrupole Kondo effect leads to non-Fermi-liquid (NFL) ground state, while the magnetic one favors ordinary Fermi-liquid (FL) ground state. In terms of the j-j coupling scheme, we argue that the orbital fluctuation must develop in the vicinity of the NFL-FL boundary. A change of temperature dependence of the f-electron entropy in both the FL and NFL regimes is demonstrated by the Wilson's numerical renormalization-group (NRG) method on the basis of the extended two-channel Kondo exchange model. We present implications to PrT2X20 (T=Ti, V, Ir; X=Al, Zn) systems which exhibit both quadrupole ordering and peculiar superconductivity. We discuss how the magnetic field lifts the non-Kramers degeneracy. Our model also represents the alternative FL state accompanied by a free magnetic spin, as a consequence of stronger competition between the magnetic and the quadrupole Kondo effects.

Highlights

In contrast to the standard heavy-fermion physics so far developed extensively in Ce-based compounds, praseodymium materials have more exotic aspects inherent in a variety of their atomic states
Nozeires and Blandin first argued this issue in view of Kondo effect, and they categorized possible ground states in terms of the magnitude of spin S and the number of scattering channels of conduction electrons nc as (i) the perfect screening, (ii) the underscreening, and (iii) the overscreening [1]
The overscreening case results in the NFL phenomena, and extensive investigations on this subject have been performed

Summary

Introduction

In contrast to the standard heavy-fermion physics so far developed extensively in Ce-based compounds, praseodymium (and uranium) materials have more exotic aspects inherent in a variety of their atomic states. Both f electrons tend to occupy Γ8 states like Fig. 1(e) in order to gain the magnetic exchange energy, J. Since the non-Kramers doublet has no magnetic dipoles, the magnetic-field effect appears in the order of h2/∆ via the excited magnetic states.

Results

Conclusion