Effect of Rare-earth Element Substitution in Superconducting R3Ni2O7 Under Pressure

Abstract Recently, high temperature ( T c ≈ 80 K) superconductivity (SC) has been discovered in La 3 Ni 2 O 7 (LNO) under pressure. This raises the question of whether the superconducting transition temperature T c could be further enhanced under suitable conditions. One possible route for achieving higher T c is element substitution. Similar SC could appear in the Fmmm phase of rare-earth (RE) R 3 Ni 2 O 7 (RNO, R = RE element) material series under suitable pressure. The electronic properties in the RNO materials are dominated by the Ni 3 d orbitals in the bilayer NiO 2 plane. In the strong coupling limit, the SC could be fully characterized by a bilayer single 3 d x 2 – y 2 -orbital t – J ∥ – J ⊥ model. With RE element substitution from La to other RE element, the lattice constant of the Fmmm RNO material decreases, and the resultant electronic hopping integral increases, leading to stronger superexchanges between the 3 d x 2 – y 2 orbitals. Based on the slave-boson mean-field theory, we explore the pairing nature and the evolution of T c in RNO materials under pressure. Consequently, it is found that the element substitution does not alter the pairing nature, i.e., the inter-layer s-wave pairing is always favored in the superconducting RNO under pressure. However, the T c increases from La to Sm, and a nearly doubled T c could be realized in SmNO under pressure. This work provides evidence for possible higher T c R 3 Ni 2 O 7 materials, which may be realized in further experiments.