Abstract
The recently discovered two-dimensional (2D) semimetal 1 T´-MoTe2 exhibits colossal magnetoresistance and superconductivity, driving a strong research interest in the material’s quantum phenomena. Unlike the typical hexagonal structure found in many 2D materials, the 1 T´-MoTe2 lattice has strong in-plane anisotropy. A full understanding of the anisotropy is necessary for the fabrication of future devices which may exploit these quantum and topological properties, yet a detailed study of the material’s anisotropy is currently lacking. While angle resolved Raman spectroscopy has been used to study anisotropic 2D materials, such as black phosphorus, there has been no in-depth study of the Raman dependence of 1 T´-MoTe2 on different layer numbers and excitation energies. Here, our angle resolved Raman spectroscopy shows intricate Raman anisotropy dependences of 1 T´-MoTe2 on polarization, flake thickness (from single layer to bulk), photon, and phonon energies. Using a Paczek approximation, the anisotropic Raman response can be captured in a classical framework. Quantum mechanically, first-principle calculations and group theory reveal that the anisotropic electron-photon and electron-phonon interactions are nontrivial in the observed responses. This study is a crucial step to enable potential applications of 1 T´-MoTe2 in novel electronic and optoelectronic devices where the anisotropic properties might be utilized for increased functionality and performance.
Highlights
Transition metal dichalcogenides (TMDCs) are two-dimensional (2D) materials that have emerged as appealing material systems due to their variable electrical band gap and strong spin-orbit coupling
Using the full quantum model based on the density functional and quantum perturbation theories, we demonstrate that the anisotropy of Raman modes is both influenced by the anisotropic electron-photon interaction and the anisotropic electron-phonon interaction
The single-layer and few-layer 1 T-MoTe2 were mechanically exfoliated from 1 T-MoTe2 crystals[14,20] onto a 285 nm SiO2/Si substrate (Fig. 1a–b). Their layer numbers were first identified by optical contrast and confirmed by atomic force microscopy (AFM)
Summary
Transition metal dichalcogenides (TMDCs) are two-dimensional (2D) materials that have emerged as appealing material systems due to their variable electrical band gap and strong spin-orbit coupling. The monoclinic 1 Tcrystal phase changes to the orthorhombic Td phase, resulting in observations of huge magnetoresistance, type-II Weyl semimetal Fermi arcs, and potentially providing a route towards the quantum spin Hall effect[14,15,16,17,18,19,20,21] Both 2 H and monoclinic 1 T-MoTe2 are stable at room temperature, and the few-layer crystals can be obtained through the chemical vapor deposition method or mechanical exfoliation[22,23]. The anisotropic Raman response’s dependence on the 1 T-MoTe2 thickness and photon excitation wavelength are carried out by rotating the incident light polarization method, while fixing the sample orientation and scattered light polarization Using this method, the polar plots of the intensities for all detected modes exhibit a two-lobed shape, while the main-axis orientations for different symmetric modes are different. Our research explores the in-plane anisotropic intensities of Raman modes in monoclinic 2D 1 T-MoTe2, and reveals the physical origin of the anisotropic Raman response, beneficial for the design of future devices which utilize the anisotropic optical, electrical, and mechanical properties of TMDCs30
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