Skyrmion-antiskyrmion lattice: A net-zero topological phase in low-symmetry frustrated chiral magnets

We report the discovery of a thermodynamically stable skyrmion-antiskyrmion lattice in two-dimensional heterostructures, a novel state exhibiting a net-zero global topological charge owing to an equal population of skyrmions and antiskyrmions. This surprising coexistence of oppositely charged solitons remarkably circumvents their anticipated annihilation. We demonstrate the formation and evolution of this phase in Fe films on ${C}_{1v}$-symmetric (110) surfaces of GaAs and CdTe semiconductors. Specifically, we reveal a series of magnetic-field-induced phase transitions: cycloidal spin-spiral $\ensuremath{\rightarrow}$ skyrmion-antiskyrmion lattice $\ensuremath{\rightarrow}$ conical spin-spiral $\ensuremath{\rightarrow}$ ferromagnet. The remarkable stability of the net-zero lattice is attributed to symmetry-enforced anisotropic magnetic interactions. Lowering interfacial symmetry to ${C}_{1v}$ thus enables frustrated chiral magnets, uniquely manifesting in thermodynamically stable net-zero topological soliton lattices, as revealed by our findings.