21 research outputs found
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
Anomalies of Heat Capacity and Phase Transitions in
In the system the specific heat has been studied in a wide range of Yb-concentration in the vicinity of the quantum critical point ≈ 0.3. The results were obtained on high quality single crystalline samples of compound placed near quantum critical point, both for antiferromagnetic metals (x ) within a wide temperature range of 1.9-300 K in magnetic field up to 9 T. The temperature dependence of the magnetic contribution to specific heat for shows a logarithmic divergence of the form /T∿-lnT at T<4 K, which may be attributed to the quantum critical regime, and it is suppressed by strong external magnetic field. The Schottky anomaly of the magnetic contribution to specific heat in has been established and analyzed in detail
Evidence of electronic phase separation in the strongly correlated semiconductor YbB12
The studies of high-quality single-domain crystals of YbB12 were carried out
by the precise x-ray diffraction technique in combination with the low
temperature polarized THz - infrared spectroscopy and accurate magnetotransport
measurements. It has been shown for the first time that this archetypal
strongly correlated system with a metal-insulator transition to a mysterious
dielectric ground state with a metal Fermi surface (Science 362, 65-69 (2018)
and ibid 362, 32-33 (2018)) is actually a heterogeneous compound in the regime
of electronic phase separation. Changes in the configuration of the discovered
dynamic charge stripes are investigated upon cooling, as a result, a conclusion
is drawn in favor of a crossover between different patterns of the filamentary
electronic structure penetrating the semiconducting matrix of YbB12. We argue
that the discovery of stripes in YbB12 is fundamental, elucidating the nature
of exotic dielectric state in Kondo insulators.Comment: 12 pages including 4 figure
Superconductivity in Dodecaborides with Cage-Glass Crystal Structure
We probed the evolution of the superconducting transition temperature and the normal state parameters of solid solutions employing resistivity, heat capacity and magnetization measurements. In these studies of high-quality single crystals it was found that there are two types of samples with different magnetic characteristics. An unusually strong suppression of superconductivity in with a rate of Lu was observed previously on the first "magnetic" set of crystals, and it was argued to be caused by the emergence of static spin polarization in the vicinity of non-magnetic lutetium ions. On the contrary, the second (current) set of "nonmagnetic" crystals demonstrates a conventional dependence with a rate of Lu which is typical for BCS-type superconductors doped by nonmagnetic impurities. The reason for this difference is yet unclear. Moreover, the H-T phase diagram of the superconducting state of (0 ≤ x ≤ 1) solid solutions has been deduced from magnetization measurements
Charge Transport and Magnetism in
Transport and magnetic properties of polycrystalline samples were investigated at temperatures 1.8-300 K in magnetic fields up to 9 T. The activated behavior of resistivity, the Hall coefficient and thermopower is described in terms of a narrow gap ≈ 16.6 meV, which controls the charge transport in at T>40 K. The maximum of magnetic susceptibility found at 50 K is shown to be induced by a spin gap Δ ≈ 4.7 meV being close to the half of the spin fluctuation energy in YbB₁₂. Large diffusive thermopower S=AT, A=-29.1 μV/K² and the Pauli susceptibility χ₀ ≈ 7.2×10¯³ emu/mol found below 20 K seem to be associated with the many-body resonance, which corresponds to states with an enhanced effective mass m* ≈ 250m₀ (m₀ - free electron mass). The effective parameters of magnetic centers and the analysis of anomalies favor the nonequivalent states of substitute Tm ions