Hall and transverse even effects in the vicinity of a quantum critical point in Tm1-xYbxB12

The angular, temperature, and magnetic field dependences of the resistance recorded in the Hall effect geometry are studied for the rare-earth dodecaboride Tm1 - x Yb (x) B-12 solid solutions where the metal-insulator and antiferromagnetic-paramagnetic phase transitions are observed in the vicinity of the quantum critical point x (c) a parts per thousand 0.3. The measurements performed on high-quality single crystals in the temperature range 1.9-300 K for the first time have revealed the appearance of the second harmonic contribution, a transverse even effect in these fcc compounds near the quantum critical point. This contribution a is found to increase drastically both under the Tm-to-ytterbium substitution in the range x > x (c) and with an increase in the external magnetic field. Moreover, as the Yb concentration x increases, a negative peak of a significant amplitude appears on the temperature dependences of the Hall coefficient R (H)(T) for the Tm1 - x Yb (x) B-12 compounds, in contrast to the invariable behavior R (H)(T) a parts per thousand const found for TmB12. The complicated activation-type behavior of the Hall coefficient is observed at intermediate temperatures for x a parts per thousand yen 0.5 with activation energies E (g) /k (B) a parts per thousand 200 K and E (a)/k (B) = 55-75 K, and the sign inversion of R (H)(T) is detected at liquid-helium temperatures in the coherent regime. Renormalization effects in the electron density of states induced by variation of the Yb concentration are analyzed. The anomalies of the charge transport in Tm1 - x Yb (x) B-12 solid solutions in various regimes (charge gap formation, intra-gap many-body resonance, and coherent regime) are discussed in detail and the results are interpreted in terms of the electron phase separation effects in combination with the formation of nanosize clusters of rare earth ions in the cage-glass state of the studied dodecaborides. The data obtained allow concluding that the emergence of Yb-Yb dimers in the Tm1 - x Yb (x) B-12 cage-glass matrix is the origin of the metal-insulator transition observed in the achetypal strongly correlated electron system of YbB12.