Superconductivity and phase separation in electrochemically hydrogenized K1−δCr3As3Hx

Abstract

We report preparation, crystal structure, and physical properties of a quasi-one-dimensional Cr-based arsenide hydride K1−δCr3As3Hx. Through an electrolysis using essentially nonsuperconducting samples as the cathode, additional hydrogen atoms can be successfully intercalated up to x=0.45 and, consequently, the in-plane and interplane Cr–Cr bond distances in the chains of face-sharing Cr octahedra increase by 3.7% and 1.5%, respectively. The electrochemically hydrogenized samples show a broad superconducting transition at Tc=5.8 K, a record in the K-Cr-As-H system, with nearly full magnetic shielding at 1.8 K. The electronic specific-heat coefficient extracted from the specific-heat measurement is as high as γn=47 mJ K−2 mol Cr−1, suggesting a stronger electron correlation that is likely to be associated with the expansions of Cr–Cr bonds. Meanwhile, the dimensionless specific-heat jump ΔC/(γnTc) is only 0.30, about 20% of the expected value in the BCS weak-coupling scenario. Furthermore, the normal-state magnetism is characterized by Curie-Weiss paramagnetism with an enhanced effective localized moment of 1.33 μB/Cr, suggesting that a nonsuperconducting phase with localized spins dominates. The H1 nuclear magnetic resonance measurement reveals two different spin-lattice relaxations, corresponding to superconducting and localized-spin phases, respectively. All the results point to phase separation with minority superconducting phase and majority nonsuperconducting phase in the quasi-one-dimensional K1−δCr3As3Hx system.

Source-reported materials — not catalogue approval

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