Effect of Ni-site substitutions in superconducting La3Ni2B2N3−δ

Abstract

We investigated the effect of Ni/Co and Ni/Cu substitutions upon the superconducting and normal state properties of La3(Ni1−xMx)2B2N3−δ (M=Co, Cu). X-ray and neutron diffraction studies reveal a limited solid solubility for Cu: (0<xCu<~0.1) and single phase compounds for 0<xCo<~0.3. From ac-, dc-susceptibility, and specific heat measurements we determined Tc, the bare density of states at the Fermi energy N(Ef), the electron-phonon mass enhancement λ, and the Stoner enhancement factor S, as a function of x. Superconductivity is suppressed to below 1.5 K for La3(Ni0.7Co0.3)2B2N3−δ while for Ni/Cu substitution only the initial depression rate, dTc/dx≃−0.23K/(mol%Cu), could be determined. The results clearly show that the suppression of superconductivity is primarily caused by the reduction of N(Ef) concomitant with a fall of the coupling strength λ, while there are no hints for other effects like magnetic pair breaking. The comparison with the results reported for Y(Ni1−xCox)2B2C shows that the electronic changes induced by Ni/Co substitution are very similar in both systems.

Source-reported materials — not catalogue approval

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