Switchable magnonic topology with transport fingerprints in two-dimensional ferromagnet CrVI₆

Topological magnons offer a charge-free platform for low-dissipation spintronic devices. However, studies on magnonic topological phase transitions (TPTs) in experimentally synthesized materials remain limited. Here, we introduce a general mechanism for achieving controllable TPTs in topological magnonics. Remarkably, successive TPTs among the normal magnon insulator (NMI), topological magnon insulator (TMI), and second-order topological magnon insulator (SOTMI) phases are realized, with distinct topological fingerprints identifying each phase, i.e., integer Chern number C and chiral edge states for TMI, whereas nonzero fractional corner charge Q⁽³⁾ and corner states for SOTMI. Combined with first-principles calculations, we demonstrate the experimentally synthesized 2D ferromagnet CrVI₆ as an ideal material realization of the proposed successive TPTs. Moreover, we find that the switchable TPTs in CrVI₆ monolayer are accompanied by pronounced and distinct changes in thermal, spin, and valley transport responses, including the magnon Hall effect, magnon Nernst effect, and their valley counterparts of magnon valley Hall effect and magnon valley Nernst effect. These transport responses not only reveal the previously overlooked TPTs, but also offer experimentally accessible means to distinguish the different magnonic topological phases.