Structural symmetry effects on the competition of density waves and superconductivity in bilayer nickelates

<title>Abstract</title> <p> We investigate the interplay between spin-density-wave (SDW) order and superconductivity in the bilayer nickelate La3Ni2O7 using the functional renormalization group (fRG) applied to multiorbital models of both the ambient- and high-pressure crystal structures. As Hund’s coupling increases, the leading instability evolves from superconductivity to an SDW state with ordering vector Q ₁ ≈ (π/2, π/2) (equivalently Q _Y ≈ (0, π) in the orthorhombic Amam Brillouin zone), in agreement with experimental observations. Surprisingly, the ambient- and high-pressure structures exhibit nearly identical non-interacting susceptibilities and leading fRG instabilities. Furthermore, we find that the emergence of superconductivity under pressure cannot be explained solely by changes in the low- energy electronic structure. Instead, our results identify the suppression of orthorhombicity as a key ingredient for superconductivity. As the system approaches the tetragonal limit, symmetry-related SDW fluctuations become nearly degenerate, frustrating long-range magnetic order while enhancing pairing interactions. These findings highlight lattice symmetry as a central tuning parameter of the competing ordered states in bilayer nickelates and suggest that reducing orthorhombicity through uniaxial strain could stabilize bulk superconductivity already at ambient pressure. </p>