Microscopic Insights to the Ultralow Thermal Conductivity of Monolayer 1T-SnTe2

TL;DR

This study uses first-principles calculations to reveal that monolayer 1T-SnTe2 has ultralow thermal conductivity due to its heavy atoms, weak bonding, and flat phonon branches, making it promising for thermoelectric applications.

Contribution

It provides a detailed microscopic understanding of the origin of ultralow thermal conductivity in monolayer 1T-SnTe2 through first-principles phonon analysis.

Findings

Ultralow lattice thermal conductivity due to flat acoustic phonon branches.

Confirmation of energetic and dynamical stability of monolayer SnTe2.

Presence of strong interband transitions and plasmonic resonance near 4.84 eV.

Abstract

Two-dimensional (2D) metallic systems with intrinsically low lattice thermal conductivity are rare, yet they are of great interest for next-generation energy and electronic technologies. Here, we present a comprehensive first-principles investigation of monolayer tin telluride (SnTe2) in its 1T (CdI2-type, P3m1) structure. Our calculations establish its energetic and dynamical stability, confirmed by large cohesive (10.9 eV/atom) and formation (-4.06 eV/atom) energies and a phonon spectrum free of imaginary modes. The electronic band structure reveals metallicity arising from strong Sn-Te p orbital hybridization. Most importantly, phonon dispersion analysis uncovers a microscopic origin for the ultralow lattice thermal conductivity: the heavy mass of Te atoms, weak Sn-Te bonding, and flat acoustic branches that yield exceptionally low and anisotropic group velocities (~5.0 x 10^3 m/s), together with the absence of a phonon bandgap that enhances Umklapp scattering. These features converge to suppress phonon-mediated heat transport. Complementary calculations of the optical dielectric response and joint density of states reveal pronounced interband transitions and a plasmonic resonance near 4.84 eV, suggesting additional optoelectronic opportunities. These findings establish monolayer SnTe2 as a 2D material whose vibrational softness naturally enforces ultralow lattice thermal conductivity, underscoring its potential for thermoelectric applications.