Temperature and Magnetic Field Dependent Raman Spectroscopy of Transition-Metal Dichalcogenides

Atomically-thin, transition-metal dichalcogenides (TMDs) offer potential for an alternative to graphene in advanced devices, owing to their unique electronic and optical properties. Such device applications require knowledge of the photo-thermal properties. Recently, we measured\footnote{R. Yan, J. R. Simpson, \textit{et al.}, ACS Nano \textbf{8}, 986 (2014).} the thermal conductivity for MoS$_2$ using a Raman-based optothermal technique. In the present work, we extend those measurements to related TMDs, including Ta-based compounds TaX$_2$, where X=Se or S, in both $1T$ and $2H$ crystallographic structures. Mechanical exfoliation from bulk crystals provides few- to single-layer flakes. We measure the Raman spectra of the exfoliated flakes using a novel magneto-Raman instrument, which affords measurement of the low-frequency vibrational modes of micron-sized samples as a function of both temperature (100 to 400)\,K and magnetic field (0 to 9)\,T. Dependence of the observed Raman-active phonons on temperature and magnetic field will be discussed and compared with earlier results on MoS$_2$.