Evidence of unconventional superconductivity in the Ni-doped NbB2 system

Abstract

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 (\leq 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 (TC) in stoichiometric NbB2 (< 1.3 K) to approximately 6.0 K. Bulk superconductivity is confirmed by magnetization, electronic transport, and specific heat measurements. Both Hc1 and Hc2 critical fields exhibit a linear dependence with reduced temperature (T/TC), 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 \leq x \leq 0.10.

arXiv commentKeywords: Multiband superconductivity; NbB2 system; Ni substitution; Linear critical fields

References in corpus (18)

• Specific Heat of Mg ^{11}B_2
• First-Principles Calculation of the Superconducting Transition in MgB2 within the Anisotropic Eliashberg Formalism
• Upper critical field pecularities of superconducting YNi2B2C and LuNi2B2C
• Limits of the upper critical field in dirty two-gap superconductors
• Order parameter of MgB_2: a fully gapped superconductor
• A review of two-band superconductivity: materials and effects on the thermodynamic and reversible mixed-state properties
• On the Ginzburg-Landau Analysis of the Upper Critical Field Hc2 in MgB2
• Anisotropies of the lower and upper critical fields in MgB${}_2$ single crystals
• High-pressure synthesis of superconducting Nb{1-x}B2 (x = 0-0.48) with the maximum Tc = 9.2 K
• Electronic structure and weak electron-phonon coupling in TaB${}_2$
• Lower Critical Field at Odds with A S-Wave Superconductivity in The New Superconductor $Mg{B}_2$
• Structure and Superconductivity in Zr-Stabilized, Nonstoichiometric Molybdenum Diboride
• Study of Ni-doping Effect of Specific Heat and Transport Properties for LaFe1-yNiyAsO0.89F0.11
• Superconductivity of Various Borides: The Role of Stretched c- Parameter
• Doping effect of Cu and Ni impurities on the Fe-based superconductor Ba0.6K0.4Fe2As2
• Effect of Ni-doping on magnetism and superconductivity in Eu0.5K0.5Fe2As2
• Theoretical Study of Electronic Structure and Superconductivity in Nb_(1-x)B_2 Alloys
• Influence of Ni doping on critical parameters of PdTe superconductor