Mirror symmetry breaking induced tunable topological phononic thermal transport in monolayer MgO via electrophononic effect

Tuning thermal transport in micro/nanomaterials is crucial for efficient thermal management in various electronic and power devices. Although topological phonons present unprecedented opportunities for controlling phononic properties, their influence on phononic thermal transport remains poorly understood, which limits their practical applications. In this work, we explore the manipulation of phonon topology and phononic thermal conductivity via an external electric field in monolayer MgO, using Boltzmann transport equations combined with a machine learning interatomic potential. Our calculations reveal that an out-of-plane electric field breaks the mirror symmetry of monolayer MgO, thereby releasing the symmetry-protected selection rules governing the scattering of flexural phonon modes. More importantly, this symmetry breaking reconstructs the phonon topology, leading to nodal-ring splitting and the emergence of chiral phonons. We further demonstrate that such topological phonon chirality modulations substantially enhance the three-phonon scattering process, resulting in a more than 50% reduction of lattice thermal conductivity under an out-of-plane electric field of 0.4 V/Å. In contrast, an in-plane electric field preserves the mirror symmetry and results in a much smaller thermal conductivity reduction of ∼16% without topological tuning, mainly due to lattice distortions. These findings establish the theoretical connection between topological physics and thermal transport performance. Our study demonstrates that external field-induced modulation of phonon topology provides an effective strategy to control thermal transport in two-dimensional materials, offering a pathway for designing tunable phononic and thermal-management devices.