Crystal symmetry breaking in thin square nanosheets of the topological insulator bismuth telluride

For potential use as a topological insulator, thin square-like Bi2Te3 nanosheets, prepared via a facile solution-based method, were subjected to detailed micro-Raman spectral measurements. The results demonstrate remarkable activation of the infrared active A(1u) mode in the Raman spectra despite the forbidden nature of the odd-parity A(1u) mode for bulk Bi2Te3 crystals. Therefore, the results unambiguously prove the crystal symmetry breaking of the thin square-like Bi2Te3 nanosheets. This study illustrates the potential applicability of microRaman spectroscopy as a powerful nanometrology tool for investigating the optical properties of topological insulators.