In situ techniques for quantum materials

Recently, quantum materials are the hottest topic in condensed matter physics. As the samples become smaller and smaller, in situ characterizations become more and more important. By combining molecular beam epitaxy (MBE) with STM, ARPES and other techniques, in situ characterizations can be achieved. With atomic precision control of growth, MBE can provide clean and smooth surfaces for STM and ARPES to study. Meanwhile, STM, ARPES and in situ techniques can also provide enough information for MBE to eliminate much of the trial and error during growth, so that one can fabricate the structures that do not exist in nature or cannot be grown by other techniques. Therefore, this kind of combined system can do some unique work which cannot be done by separate instruments.In this talk, I will introduce several works done with the combined system to demonstrate the strong power of the combination. With help of STM, artificial cluster crystals, i.e. a periodical array of identical nanoclusters can be grown with precise control. Atomically flat Pb thin films, stanene etc. can be grown with MBE and studied with STM. In Pb films on Si(111), we found quantum well states (QWS) form due to the electronic confinement in the film normal direction and novel properties induced by QWS. We also found high quality topological insulator films can be grown with MBE. Standing waves and Landau levels were observed with low temperature STM and demonstrated the existing of the topological surface states and the prohibition of backward-scattering. Topological insulator/superconductor hetero structures are also fabricated for exploring Majorana fermions.