Phonon-enhanced metastable melting of magnetic order in a quantum spin liquid candidate

While thermal effects from above bandgap excitations are known to melt magnetic order, the role of selectively populating low-energy elementary excitations remains poorly understood. We report photoinduced magnetic melting dynamics in Na₂Co₂TeO₆, a frustrated Kagome lattice antiferromagnet with strong Kitaev interactions proximate to a quantum spin liquid phase. Using time-resolved optical spectroscopy, we reveal a striking dichotomy in melting efficiency between near-infrared and terahertz (THz) excitation: THz pulses achieve equivalent magnetic disordering with 1000-fold reduced fluence and produce markedly longer-lived disordered states compared to near-infrared excitation. Through systematic double-pump experiments, we identify the underlying mechanism as phonon-mediated melting, wherein THz-excited coherent phonons provide an efficient pathway for magnetic order destruction that circumvents the electronic heating characteristic of optical melting. The dramatic enhancement of melting efficiency and lifetime via the phonon channel demonstrates that spin-lattice coupling plays a crucial role in the magnetic ordering of frustrated magnets and hints towards a phonon-induced nonequilibrium state. Our results establish coherent phonon excitation as a selective tool for probing and manipulating competing magnetic ground states in quantum materials.