Previous studies have shown that among binary zinc-blende compounds, mercury telluride (HgTe) exhibits exceptionally low lattice thermal conductivity $\left({\kappa }_L\right)$ despite its rather simple crystal structure; however, the underlying heat transfer mechanism remains elusive. Here, we combine self-consistent phonon calculations with the Boltzmann transport equation to investigate the anharmonic lattice dynamics and thermal transport mechanisms in HgTe, with particular emphasis on the role of four-phonon scattering. The results unveil that phonon renormalization arising from both cubic and quartic anharmonicities is indispensable for accurately describing phonon frequencies and lifetimes at finite temperatures. Notably, the renormalization effects exhibit opposite sensitivities to three- and four-phonon scattering processes for heat-carrying acoustic modes, resulting in only a modest net enhancement of ${\kappa }_L$ relative to the harmonic approximation. Moreover, we identify exceptionally strong four-phonon scattering for transverse acoustic phonon modes, driven by large quartic anharmonicity and nearly parallel phonon branches that facilitate four-phonon Fermi resonance. This strong four-phonon effect causes a dramatic reduction in ${\kappa }_L$—by 43% at 100 K—in stark contrast to most known materials, where four-phonon scattering typically becomes relevant only at elevated temperatures. Our study not only elucidates the microscopic mechanisms governing thermal transport in HgTe, but also provides guidance for the rational design of new low-${\kappa }_L$ materials.

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• Anharmonic lattice dynamics
• Lattice thermal conductivity
• Ab initio molecular dynamics
• Density functional calculations