Vector Magnonics: Electrical Injection and Control of Spin Flow in Altermagnets

Altermagnets host chirally split magnons that promise unique functionalities for information processing. However, their distinctive transport signatures, crucial for experimental identification and manipulation, remain elusive. Here, we predict that a spin accumulation electrically injects a ``vector" or multidirectional magnon spin current into an altermagnet, comprising both longitudinal and sizable transverse components. Notably, this transverse current exhibits a sign reversal away from the source and can be switched on or off by reorienting the Néel vector. While such a transverse current is found to be not forbidden even in conventional antiferromagnets, we demonstrate through quantum-kinetic calculations that in altermagnets, the transverse response is enhanced by two orders of magnitude due to broken parity-time symmetry. This giant enhancement provides a decisive transport fingerprint for detecting magnon spin splitting and Néel-vector orientation, offering a clear criterion to experimentally distinguish altermagnets from conventional antiferromagnets.