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ORAL CONTRIBUTIONS
Possibility of unconventional behavior in a new superconductor
material of Zr 1-x V x B 2 compounds.
S.T. Renosto 1 , O.V. Cigarroa 1 , Z. Fisk 2 , C.A.M. Santos 1 , J.A. Aguiar 3 , S.G. Jung 4 , J.
Vanacken 4 , V.V. Moshchalkov 4 , A.J.S. Machado 1
1 Escola de Engenharia de Lorena, Universidade de São Paulo,P.O. Box 116, Lorena – SP,
Brazil.
2 Departament of Physics and Astronomy, University of Califórnia at Irvine,92697, Irvine – CA,
USA.
3 Departamento de Física, Universidade Federal de Pernambuco, Recife – PE, Brazil.
4 Institute for Nanoscale Physics and Chemistry, K. U. Leuven Celest. 200 D, B-3001 Leuven,
Belgium;
Since the discovery of superconductivity in MgB2 with superconducting critical
temperature close to 40 K, MB2 materials (M = Transition Metal) with the same
prototype structure AlB2 are considered as candidates for multiband superconductivity.
In this group, the ZrB2 compound exhibits Pauli paramagnetism at low temperature.
However, in this work we show results of a systematic study of the partial substitution
of Zr for V in the Zr1-xVxB2 (0.01 ≤ x ≤ 0.1) compositions which reveal that vanadium is
able to induce superconductivity in this compound with superconducting critical
temperature reaching the maximum value of 8.7 K for Zr0.96V0.04B2 composition.
Measurements of the dependence of resistivity, magnetization and specific heat with
temperature for polycrystalline samples, and magnetization versus temperature for
single crystal sample, confirm the superconducting transition close to 9.0 K. These
results reveal the strongly deviation from conventional (BCS) behavior through of
specific heat and transport measurements. We were found a possibility of an
unconventional behavior in the negative curvature of the Hc1 versus reduced temperature
(T/Tc) phase diagram, which suggest multiband behavior. This kind of behavior it is
relatively common in compounds which crystallize in AlB2 prototype structure. Indeed,
these suspect is verify in magnetization versus temperature for single crystal of this
material, where we can observe a second transition close to 3.0 K. Probably this is
consequence of the π band between boron-boron interaction, which is amplify with
vanadium doping which is smaller that zirconium atoms. Furthermore, the size of the
jump in the specific heat is smaller that the value predict by BCS theory.
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