Evidence of unconventional superconductivity in the Ni-doped NbB2 system

JOURNAL OF ALLOYS AND COMPOUNDS

卷:787

Article

Renosto, S. T.¹  Lang, R.²  Diez, E.¹  Correa, L. E.³  da Luz, M. S.⁴  Fisk, Z.⁵  Machado, A. J. S.³ 

[1] Univ Salamanca, Dept Fis Fundamental, Nanolab, Grp Nanotecnol, E-37008 Salamanca, Spain

[2] Univ Fed Sao Paulo, Inst Ciencia & Tecnol, BR-12231280 Sao Jose Dos Campos, Brazil

[3] Univ Sao Paulo, Dept Mat, BR-12602810 Lorena, Brazil

[4] Univ Fed Triangulo Mineiro, BR-38066200 Uberaba, Brazil

[5] Univ Calif Irvine, Dept Phys & Astron, Irvine, CA 92697 USA

关键词: Multiband superconductivity;    Linear critical fields;    Specific heat;    NbB2 compound;    Ni-doping;   

DOI  :  10.1016/j.jallcom.2019.02.072

来源: Elsevier

【 摘 要 】

In this paper, a comprehensive study of the effects of Ni-doping on structural, electrical, thermal and magnetic properties of the NbB2 is presented. Low amounts (<= 10%) of Ni substitution on Nb sites cause structural distortions and induce drastic changes in the physical properties, such as the emergence of a bulk superconducting state with anomalous behaviors in the critical fields (lower and upper) and in the specific heat. Ni-doping at the 9 at.% level, for instance, is able to increase the critical temperature (T-c) in stoichiometric NbB2 (<1.3 K) to approximately 6.0 K. Bulk superconductivity is confirmed by magnetization, electronic transport, and specific heat measurements. Both H-c1 and H-c2 critical fields exhibit a linear dependence with reduced temperature (T/T-c), and the specific heat deviates remarkably from the conventional exponential temperature dependence of the single-band BCS theory. These findings suggest multiband superconductivity in the composition range from 0.01 <= x <= 0.10 (Nb1-xNixB2). (C) 2019 Elsevier B.V. All rights reserved.

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