Single-crystal growth and superconductivity in RbNi2Se2

Herein we report the synthesis and characterization of RbNi₂Se₂, an analog of the iron chalcogenide superconductor Rb_xFe₂Se₂, via transport, angle-resolved photoemission spectroscopy, and density functional theory calculations. A superconducting transition at T_c=1.20 K is identified. In the normal state, RbNi₂Se₂ shows paramagnetic and Fermi-liquid behaviors. A large Sommerfeld coefficient yields an effective electron mass of m* ≈ 6m_e. In the superconducting state, zero-field electronic specific-heat data C_es can be described by a two-gap BCS model, indicating that RbNi₂Se₂ is a possible multigap superconductor. Our density functional theory calculations and angle-resolved photoemission spectroscopy measurements demonstrate that RbNi₂Se₂ exhibits relatively weak correlations and multiband characteristics, consistent with the multigap superconductivity.