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102 results on '"Paderno, Yu. B."'

43. Superconductivity mediated by a soft phonon mode: specific heat, resistivity, thermal expansion and magnetization of YB6

Author

Lortz, R., Wang, Y., Tutsch, U., Abe, S., Meingast, C., Popovich, P., Knafo, W., Shitsevalova, N., Paderno, Yu. B., and Junod, A.

Subjects
Superconductivity (cond-mat.supr-con), Condensed Matter - Materials Science, Condensed Matter::Superconductivity, Condensed Matter - Superconductivity, Materials Science (cond-mat.mtrl-sci), FOS: Physical sciences
Abstract

The superconductor YB6 has the second highest critical temperature Tc among the boride family MBn. We report measurements of the specific heat, resistivity, magnetic susceptibility and thermal expansion from 2 to 300 K, using a single crystal with Tc = 7.2 K. The superconducting gap is characteristic of medium-strong coupling. The specific heat, resistivity and expansivity curves are deconvolved to yield approximations of the phonon density of states, the spectral electron-phonon scattering function and the phonon density of states weighted by the frequency-dependent Grueneisen parameter respectively. Lattice vibrations extend to high frequencies >100 meV, but a dominant Einstein-like mode at ~8 meV, associated with the vibrations of yttrium ions in oversized boron cages, appears to provide most of the superconducting coupling and gives rise to an unusual temperature behavior of several observable quantities. A surface critical field Hc3 is also observed., 29 pages, 5 tables, 17 figures. Accepted for publication in Phys. Rev. B

Published
2005

44. On the problem of the Kondo-lattice model application to CeB6

Author

Sluchanko, N. E., Bogach, A. V., Glushkov, V. V., Demishev, S. V., Ignatov, M. I., Paderno, Yu. B., Samarin, N. A., and Shitsevalova, N. Yu.

Subjects
Condensed Matter - Strongly Correlated Electrons, Strongly Correlated Electrons (cond-mat.str-el), FOS: Physical sciences, Condensed Matter::Strongly Correlated Electrons
Abstract

Precision measurements of charge transport parameters (resistivity, Hall and Seebeck coefficients) have been carried out on high-quality single-crystals of cerium hexaboride in a wide temperature range 1.8-300 K. It is shown that in the temperature interval of 5 K < T < T* = 80 K the magnetic contribution in resistivity obeys the power law rm = T -1/n, which corresponds to the regime of weak localization of charge carriers with the critical index 1/n = 0.39 +- 0.02. In the same temperature interval an asymptotic behavior of thermopower S = -lnT is found together with an essential decrease of the charge carriers mobility in CeB6. A negative Hall coefficient anomaly has been detected at liquid helium temperatures. The data obtained are compared with the results predicted by the Kondo-lattice model and discussed also in terms of the theory of excitonic ferromagnetism.

Published
2005

45. Specific heat, magnetic susceptibility, resistivity and thermal expansion of the superconductor ZrB12

Author

Lortz, R., Wang, Y., Abe, S., Meingast, C., Paderno, Yu. B., Filippov, V., and Junod, A.

Subjects
Superconductivity (cond-mat.supr-con), Condensed Matter - Superconductivity, FOS: Physical sciences
Abstract

In an attempt to clarify conflicting published data, we report new measurements of specific heat, resistivity, magnetic susceptibility, and thermal expansivity up to room temperature for the 6 K superconductor ZrB12, using well-characterized single crystals with a residual resistivity ratio >9. The specific heat gives the bulk result 2*delta(0)/(k_B*Tc)=3.7 for the superconducting gap ratio, and excludes multiple gaps and d-wave symmetry for the Cooper pairs. The Sommerfeld constant gamma_n = 0.34 mJ K-2 gat-1 and the magnetic susceptibility xsi = -2.1 x 10^-5 indicate a low density of states at the Fermi level. The Debye temperature theta_D is in the range 1000-1200 K near zero and room temperature, but decreases by a factor of ~2 at ~35 K. The specific heat and resistivity curves are inverted to yield approximations of the phonon density of states F(omega) and the spectral electron-phonon scattering function alpha_tr^2 F(omega), respectively. Both unveil a 15 meV mode, attributed to Zr vibrations in oversized B cages, which gives rise to electron-phonon coupling. The thermal expansivity further shows that this mode is anharmonic, while the vanishingly small discontinuity at Tc establishes that the cell volume is nearly optimal with respect to Tc., v3: minor changes in the thermal expansion paragraph submitted to Physical Review B

Published
2005

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