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arXiv · 2606.06680

Symmetry-Protected Phonon Topology and Low Lattice Thermal Conductivity in Square-Octagonal Chalcogenides

Nair Surabhi Suresh·Mondal Chiranjith·Alam Aftab·Singh Nirpendra
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Abstract

Unconventional lattice geometries provide an effective platform for realizing symmetry-protected topological phonon states that can strongly influence lattice heat transport. In this work, we explore the relationship between topological phonon band features and thermal transport in square--octagonal (so) chalcogenide monolayers, namely MoS2 and SnS, by combining first-principles calculations with phonon Boltzmann transport theory. Symmetry analysis reveals the presence of nontrivial phonon band topology in the form of symmetry-protected nodal lines. Crossings between nodal lines carrying different symmetry eigenvalues produce fourfold Dirac points that enhance the phonon group velocity (vg), whereas nearly flat nodal lines lead to strong suppression of vg. The coexistence of these features, together with substantial phonon softening and enhanced anharmonic scattering around the topological band crossings, markedly suppresses the lattice thermal conductivity ($\kappa_l$). As a result, room-temperature $\kappa_l$ values of 4.0 W/mK for so-SnS and 18.7 W/mK for so-MoS2 are obtained, representing reductions by more than a factor of two and eight, respectively, relative to their hexagonal phases. Our results uncover a direct connection between phonon band topology and heat transport in two-dimensional materials, highlighting lattice symmetry and topological band engineering as promising routes for tailoring thermal properties. These findings further suggest opportunities for designing topological phononic and thermoelectric devices with controllable heat flow.

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Nair Surabhi Suresh, Mondal Chiranjith, Alam Aftab, Singh Nirpendra. 2026-06-04. Symmetry-Protected Phonon Topology and Low Lattice Thermal Conductivity in Square-Octagonal Chalcogenides. https://arxiv.org/abs/2606.06680

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