Bulk and local magnetic susceptibility of ErB12

High precision measurements of magnetoresistance Δρ/ρ = f(T,H) and magnetization M(T,H) were carried out on single crystals of rare-earth dodecaboride $ErB_{12}$ at temperatures in the interval 1.8-30 K in magnetic fields up to 70 kOe. The high accuracy of the experiments allowed us to perform numerical differentiation and analyze quantitatively the behavior of the derivative d(Δρ/ρ)/dH = f(T,H) and of the magnetic susceptibility χ(T,H) = dM/dH in paramagnetic and magnetically ordered (antiferromagnetic, $T_N$ ≈ 6.7 K and $T_M$ ≈ 5.85 K) phases of $ErB_{12}$. It was shown that negative magnetoresistance anomalies observed in present study in paramagnetic state of $ErB_{12}$ may be consistently interpreted in the framework of a simple relation between resistivity and magnetization -Δρ/ρ ~ $M^2$

Hall effect in the vicinity of quantum critical point in Tm1-xYbxB12

The angular, temperature and magnetic field dependences of Hall resistance roH for the rare-earth dodecaboride solid solutions Tm1-xYbxB12 have been studied in a wide vicinity of the quantum critical point (QCP) xC~0.3. The measurements performed in the temperature range 1.9-300 K on high quality single crystals allowed to find out for the first time in these fcc compounds both an appearance of the second harmonic contribution in ro2H at QCP and its enhancement under the Tm to ytterbium substitution and/or with increase of external magnetic field. When the Yb concentration x increases a negative maximum of a significant amplitude was shown to appear on the temperature dependences of Hall coefficient RH(T) for the Tm1-xYbxB12 compounds. Moreover, a complicated activation type behavior of the Hall coefficient is observed at intermediate temperatures for x>0.5 with activation energies Eg~200K and Ea~55-75K in combination with the sign inversion of RH(T) at low temperatures in the coherent regime. The density of states renormalization effects are analyzed within the variation of Yb concentration and the features of the charge transport in various regimes (charge gap formation, intra-gap manybody resonance and coherent regime) are discussed in detail in Tm1-xYbxB12 solid solutions.Comment: 38 pages including 10 figures, 70 reference

Electronic polarons in an extended Falicov-Kimball model

We examine the one-dimensional spinless Falicov-Kimball model extended by a hybridization potential between the localized and itinerant electron states. Below half-filling we find a crossover from a mixed-valence metal to an integer-valence phase separated state with increasing on-site Coulomb repulsion. This crossover regime is characterized by local competition between the strong- and weak-coupling behaviour, manifested by the formation of an electronic polaron liquid. We identify this intermediate-coupling regime as a charge-analogy of the Griffiths phase; a phase diagram is presented and discussed in detail.Comment: RevTex, 10 pages, 1 figure; revised discussio