Adatom engineering magnetic order in superconductors: Applications to altermagnetic superconductivity

TL;DR

This paper theoretically demonstrates how adatom superlattices on unconventional superconductors can induce novel magnetic and pairing states with unique symmetry properties, including orbital-altermagnetic superconductivity.

Contribution

It introduces the concept of orbital-altermagnetic superconductivity stabilized by adatom superlattices, revealing new magnetic and topological features in superconducting states.

Findings

Stabilization of orbital-altermagnetic superconductor with loop currents

Presence of non-zero Berry curvature quadrupole moment

Spin-orbit coupling induces spin splitting and complex spin textures

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 non-trivial 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 four-fold rotations. This state is further characterized by a non-zero Berry curvature quadrupole moment and, upon including spin-orbit coupling, by an altermagnetic spin splitting of the bands and non-trivial spin textures in the superlattice unit cell, with zero net spin moment.