Hidden Quantum Circulation in Collinear Altermagnets

Oct. 28, 2026 (Wed.) at 3PM (ET)

Vincent Flynn

Boston College

How can a magnet support circulating spin currents while its classical magnetic order remains perfectly collinear? In this talk, I will show that this counterintuitive behavior can arise from quantum fluctuations in a centrosymmetric altermagnet.

I will consider a minimal model of the inverse Lieb lattice realized, for instance, in the altermagnetic insulator La$_2$O$_3$Mn$_2$Se$_2$. Although the ground state is a conventional collinear G-type antiferromagnet, a symmetry-allowed, locally staggered Dzyaloshinskii-Moriya interaction generates complex two-magnon pairing in the quantum vacuum. The resulting anomalous magnon pairing amplitude vanishes at the high-symmetry $X$ and $Y$ points of the Brillouin zone and exhibits vortices with opposite winding numbers. These vortices imprint onto spin correlations and cannot be removed by a smooth global choice of spin frame, revealing a form of gauge-irremovable frustration that is invisible in the static spin configuration.

I will further show how this momentum-space vortex structure manifests in real space as an antiferrochiral pattern of equilibrium spin currents: neighboring plaquettes support counter-circulating currents, giving zero net flow while retaining a nontrivial local circulation. This structure can be understood equivalently through Wilson-loop fluxes of an emergent U(1) gauge field associated with magnon pairing. I will discuss possible experimental signatures and the broader implications for hidden orders, altermagnetism, and frustrated quantum matter.