Anomalous in-plane lattice thermal conductivity in an atomically thin two-dimensional α-GeTe layer

Unexpected thermal transport properties of MgSiO3monolayer at extreme conditions

The thermal transport properties of mantle minerals are of paramount importance to understand the thermal evolution processes of the Earth. Here, we perform extensively structural searches of two-dimensional MgSiO3monolayer by CALYPSO method and first-principles calculations. A stable MgSiO3monolayer withPmm2 symmetry is uncovered, which possesses a wide indirect band gap of 4.39 eV. The calculations indicate the lattice thermal conductivities of MgSiO3monolayer are 49.86 W (mK)-1and 9.09 W (mK)-1inxandydirections at room temperature. Our findings suggest that MgSiO3monolayer is an excellent low-dimensional thermoelectric material with highZTvalue of 4.58 from n-type doping in theydirection at 2000 K. The unexpected anisotropic thermal transport of MgSiO3monolayer is due to the puckered crystal structure and the asymmetric phonon dispersion as well as the distinct electron states around the Fermi level. These results offer a detailed description of structural and thermal transport properties of MgSiO3monolayer at extreme conditions.

Anisotropy and thermal properties in GeTe semiconductor by Raman analysis

Low-symmetric GeTe semiconductors have attracted wide-ranging attention due to their excellent optical and thermal properties, but only a few research studies are available on their in-plane optical anisotropic nature that is crucial for their applications in optoelectronic and thermoelectric devices. Here, we investigate the optical interactions of anisotropy in GeTe using polarization-resolved Raman spectroscopy and first-principles calculations. After determining both armchair and zigzag directions in GeTe crystals by transmission electron microscopy, we found that the Raman intensity of the two main vibrational modes had a strong in-plane anisotropic nature; the one at ∼88.1 cm-1 can be used to determine the crystal orientation, and the other at ∼124.6 cm-1 can reveal a series of temperature-dependent phase transitions. These results provide a general approach for the investigation of the anisotropy of light-matter interactions in low-symmetric layered materials, benefiting the design and application of optoelectronic, anisotropic thermoelectric, and phase-transition memory devices based on bulk GeTe.