Thermal conductivity and tunable thermal anisotropy of magnetic CrSBr monolayer

Abstract

We present first-principles calculations of the thermal conductivity, ${\bm κ}$, of monolayer CrSBr, a van der Waals magnetic 2D material. We find a considerable thermal anisotropy, with a ratio $κ_{xx}/κ_{yy}$ of around 1.8. The anisotropy stems from a combined effect of phonon velocities and lifetimes and can be tuned by controlling the flake size by suppressing long mean path phonons.

Figures (4)

• Figure 1: (a) Top and (b) side views of ML CrSBr; Cr, S, and Br atoms are represented by blue, yellow, and brown spheres, respectively; $d$ indicates the distance between Br planes.
• Figure 2: (a) Phonon dispersion. (b) Thermal conductivity as a function of temperature. (c) $\Delta v = v_x - v_y$ and (d) $\Delta \tau = \tau_x - \tau_y$ as a function of frequency; before subtraction, velocities and lifetimes were averaged over intervals of 1 THz. Phonon lifetimes, $\tau_i$ with $i = x,y$ (see text for definition) are computed at 150 K.
• Figure 3: (Left) Thermal conductivity as a function of temperature of ML CrSBr of different characteristic size, $L$. (Right) Anisotropy ratio as a function of $L$ at $T=100$ and 150 K.
• Figure 4: $\Delta \tau = \tau_x - \tau_y$ as a function of frequency for (a) $L = \infty$ (b) 10 $\mu$m, and (c) 100nm; before subtraction, lifetimes were averaged over intervals of 1 THz. Phonon lifetimes, $\tau_i$ with $i = x,y$ (see text for definition) are computed at 150 K. (d) Ratio between the cumulative thermal conductivity, $\kappa_{xx}$ and $\kappa_{yy}$, as a function of the MFP, $\Lambda$, where $\kappa(\bar{\Lambda})$ is defined as the thermal conductivity considering only phonons with MFP $\Lambda < \bar{\Lambda}$.