Alireza Akbari, Peter Thalmeier
The heavy fermion metal CeB6 exhibits hidden order of antiferroquadrupolar
(AFQ) type below T_Q=3.2K and subsequent antiferromagnetic (AFM) order at
T_N=2.3K. It was interpreted as ordering of the quadrupole and dipole moments
of a $\Gamma_8$ quartet of localised Ce $4f^1$ electrons. This established
picture has been profoundly shaken by recent inelastic neutron scattering (G.
Friemel et al., arXiv:1111.4151) that found the evolution of a feedback spin
exciton resonance within the hidden order phase at the AFQ wave vector which is
stabilized by the AFM order. We develop an alternative theory based on a
fourfold degenerate Anderson lattice model, including both order parameters as
particle-hole condensates of itinerant heavy quasiparticles. This explains in a
natural way the appearance of the spin exciton resonance and the momentum
dependence of its spectral weight, in particular around the AFQ vector and its
rapid disappearance in the disordered phase. Analogies to the feedback effect
in unconventional heavy fermion superconductors are pointed out.
View original:
http://arxiv.org/abs/1202.4291
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