Effects of bonding on superconductivity in Sr(Ni_1−xRh_x)₂P₂ single crystals

Bond formation and bond breaking in crystalline intermetallic solids can strongly impact properties associated with delocalized electrons, such as itinerant magnetism and superconductivity. This has been observed on numerous occasions in materials with collapsed tetragonal transitions [1,2,3]. Although SrNi₂P₂ adopts the common ThCr₂Si₂ structure for T ≥ 325 K, being in an uncollapsed tetragonal (ucT) state, it is a special case for the ThCr₂Si₂ class: on cooling below 325 K it adopts a one-third collapsed orthorhombic (tcO) phase where one out of every three P-rows bond across the Sr layers [4,5]. It is also known for exhibiting bulk superconductivity at 1.4 K at ambient pressure [6]. We find that Rh substitution in SrNi₂P₂ causes a rapid decrease of the one-third collapse transition temperature, as well as an enhancement of superconductivity.

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