Evidence for spin droplets (ferrons) formation in the heavy fermion metal CeB6 with dynamic charge stripes

The presented studies of resistivity (ρ), thermal conductivity (κ) and specific heat (C) at low temperature 1.8−7 K in magnetic field up to 90 kOe made it possible to detect for the first time the exponential field dependences ρ(H), κ ⁻¹(H), C(H) ∼ exp(−μ_effH/k_BT) of the charge transport and thermal characteristics in the so-called antiferroquadrupole (AFQ) phase of the archetypal heavy-fermion CeB₆ hexaboride. From magnetoresistance measurements it is shown that in the AFQ state the effective magnetic moment varies in the range μ_eff(T) = 1.4−1.9μ_B, and its value is very close to μ_eff(τ)(T) ≈ 2μ_B, derived from the field dependence of the relaxation time τ(H) observed in the heat capacity and thermal conductivity experiments. The phenomenological model proposed here allowes us to attribute the magnetic moments to spin droplets (ferrons), that appear in the bulk AFQ phase of CeB₆ crystals. The relevant electronic phase separation at the nanoscale, manifested by dynamic charge stripes, that leads to the formation of ferrons, was revealed from the analysis of low-temperature X-ray diffraction experiments using the maximum entropy method. We argue that the Jahn−Teller collective mode of B₆ clusters is responsible for the formation of charge stripes formation inducing transverse quasi-local vibrations of pairs and triplets of Ce ions, which leads to 4f−5d spin fluctuations providing spin-polarons (ferrons) in the CeB₆ matrix.