Reversible nonrelativistic magnon spin transport in ferroelastic altermagnets

Magnons in antiferromagnetic (AFM) insulators facilitate low-dissipation, stray-field-free spin transport. However, achieving nonvolatile, field-free control over magnon spin currents remains elusive. Here, based on symmetry analysis, we propose a universal mechanism for the active manipulation of magnon spin transport via ferroelastic transitions in two-dimensional (2D) altermagnets (AMs)-a class of unconventional AFMs simultaneously exhibiting compensated magnetization and nonrelativistic spin splitting. We show that these transitions effectively reorient principal crystal axes and modulate the underlying magnetic exchange anisotropy. Consequently, this magnetoelastic coupling drives nonrelativistic anisotropic spin transport that is ferroelastically switchable without the need for external magnetic fields or Berry curvature, leading to sign reversals in the spin Seebeck and spin Nernst conductivities. We validate this mechanism using first-principles calculations and spin-model analyses of an AM CoTe2 monolayer. Our findings establish a symmetry-based magnetoelastic paradigm for the nonvolatile control of magnon spin transport in 2D AMs, opening new avenues toward energy-efficient, reconfigurable AFM magnonic devices.