The temperature-dependent ([Formula: see text]) optical constants of monolayer [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] were investigated through spectroscopic ellipsometry over the spectral range of 0.73-6.42 eV. At room temperature, the spectra of refractive index exhibited several anomalous dispersion features below 800 nm and approached a constant value of 3.5-4.0 in the near-infrared frequency range. With a decrease in temperature, the refractive indices decreased monotonically in the near-infrared region due to the temperature-dependent optical band gap. The thermo-optic coefficients at room temperature had values from [Formula: see text] to [Formula: see text] for monolayer transition metal dichalcogenides at a wavelength of 1200 nm below the optical band gap. The optical band gap increased with a decrease in temperature due to the suppression of electron-phonon interactions. On the basis of first-principles calculations, the observed optical excitations at 4.5 K were appropriately assigned. These results provide basic information for the technological development of monolayer transition metal dichalcogenides-based photonic devices at various temperatures.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: H.L.L. thanks the Ministry of Science and Technology of Republic of China for its financial support under Grant-MOST 108-2112-M-003-013. T.Y. acknowledges the National Key R&D Program of China (2017YFA0206301) and the Major Program of Aerospace Advanced Manufacturing Technology Research Foundation NSFC and CASC, China (U1537204). H.G. acknowledges NSFC grant-51702146 and the Liaoning Province Doctor Startup Fund (201601325). R.S. acknowledges MEXT-Japan for Grant-JP18H01810. L.J.L. thanks the Taiwan Consortium of Emergent Crystalline Materials (TCECM), the Ministry of Science and Technology, and USA AFOSR BRI (FA238615100015).