Strain-induced selective transformation of topological phonons in PdAs2 and its impact on thermal transport

Exploring and regulating topological states is a longstanding hotspot in condensed matter physics and materials science. Recently, the coexistence and strain-induced transformation of topological phonons have attracted growing attention, yet their specific role in thermal transport remains rarely clarified. Based on the symmetry analysis and first-principles calculations, we first identify the coexistence of diverse topological phonons in PdAs2: quadratic contact triply degenerate points (QCTPs), Dirac nodal-lines (DNLs), double-degenerate nodal-lines (NLs), and nodal-surfaces (NSs). A central finding is the strain-induced selective transformation of these topological phonons: applying c-axis tensile strain drives the space group of PdAs2 to transform from Pa-3 to Pbca, leading to the breaking of QCTPs and double-degenerate NLs, while DNLs and NSs remain stable with their topological characteristics preserved. This selective transformation modulates thermal transport via two synergistic mechanisms: the splitting of QCTPs and double-degenerate NLs reduces the phonon scattering rate (by decreasing the number of available scattering channels) and increases the effective phonon group velocity (by increasing the number of active vibrational modes). Consequently, PdAs2’s lattice thermal conductivity is enhanced from 4.94 to 9.61 W/m K, achieving a 94.53% improvement. Our work uncovers the strain-induced selective transformation of coexisting topological phonons in PdAs2 and clarifies their thermal transport regulatory mechanism, offering new insights for topological phonons.