Superconductivity in oxygen deficient LaNiAsO1−δ (δ = 0–0.3)

• Oxygen deficiency effect on LaNiAsO was studied for the first time.
• Oxygen deficiency level (δ) to 0.3 could retain the host structure well.
• The specific heat data indicated a conventional BCS-type superconductivity.
• The replacement of La by Sm failed to improve the Tc.

LaNiAsO itself is a superconductor with a Tc of ∼2.7 K. Oxygen deficiency could be introduced up to a level of δ = 0.3 with retaining the host structure and increase the Tc to ∼4.1 K at δ = 0.3. The Tc of LaNiAsO1−δ monotonically increases with increasing δ and changes negligibly when δ > 0.3. Using the measured values of the lower critical field Hc1, the upper critical field Hc2, and the specific heat Cp, we estimated the thermodynamic critical field Hc(0), coherence length ξ(0), penetration depth λ(0), the Ginzburg–Landau parameter κ(0), and the electron–phonon coupling constant λep for LaNiAsO0.7 with an optimal Tc. The specific heat data follow a BCS-like exponential decrease below Tc, indicating a fully gapped superconductivity. In addition, the replacement of La by Sm failed to enhance the Tc. The many differences distinguish LaNiAsO from the 1 1 1 1-type Fe-based superconductors, thus highlighting the importance of Fermi surface topology for superconductivity.

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