1 Aarhus University2 Interdisciplinary Nanoscience Center - INANO-Fysik, Ny Munkegade, Interdisciplinary Nanoscience Center, Science and Technology, Aarhus University3 Tsinghua University4 Tsinghua University5 Department of Clinical Medicine - Anæstesisektor Nordjylland, Department of Clinical Medicine, Health, Aarhus University6 Peking University7 Department of Clinical Medicine - Anæstesisektor Nordjylland, Department of Clinical Medicine, Health, Aarhus University
Topological insulators (TIs) are a new state of quantum matter with a band gap in bulk and conducting surface states. In this work, the Raman spectra of topological insulator Bi2Te3 films prepared by molecular beam epitaxy (MBE) have been measured by an in situ ultrahigh vacuum (UHV)-MBE-Raman spectroscopy system. When the thickness of Bi2Te3 films decreases from 40 quintuple-layers (QL) to 1 QL, the spectral characteristics of some Raman modes appearing in bulk Bi2Te3 vary and a new vibrational mode appears, which has not been reported in previous studies and might be related to quantum size effects and symmetry breaking. In addition, an obvious change was observed at 3 QL when a Dirac cone formed. These results offer some new information about the novel quantum states of TIs.