Adatom Engineering Magnetic Order in Superconductors: Applications to Altermagnetic Superconductivity
Lucas V. Pupim, Mathias S. Scheurer
Abstract
We study theoretically how superlattices based on adatoms on surfaces of unconventional superconductors can be used to engineer novel pairing states that break time-reversal symmetry and exhibit nontrivial magnetic point symmetries. We illustrate this using a square-lattice Hubbard model with d-wave superconductivity and a subleading s-wave state as an example. An adatom superlattice with square-lattice symmetries is shown to stabilize an "orbital altermagnetic superconductor," a state that exhibits loop current patterns and associated orbital magnetic moments, which preserve superlattice translations but are odd under fourfold rotations. This state is further characterized by a nonzero Berry curvature quadrupole moment and, upon including spin-orbit coupling, by an altermagnetic spin splitting of the bands and nontrivial spin textures in the superlattice unit cell, with zero net spin moment.