In situ growth and characterization of topological insulator thin films and heterostructures
Topological insulators (TIs) are a novel state of matter for which the bulk is insulating while the surface is conducting as a necessary consequence of the characteristics of the bulk material. The metallic surface states are topologically protected and show a variety of exotic properties. For example, exceptional transport phenomena, like the quantum anomalous Hall effect, can be induced or Majorana states can be created in proximity to magnets or superconductors. An inherent issue, however, hinders the experimental investigation or a potential application in spintronics or quantum computing: There is often no direct access to purely topologically surface states by electrical transport measurements. The ideal TI is bulk insulating and the Dirac point is exposed and close to the Fermi level. However, most materials do not naturally show these characteristics. Moreover, an exposure to air considerably changes the band structure making an in situ characterization or a carefully chosen capping layer necessary.
Our unique ultra-high vacuum system in Dresden consists of two molecular beam epitaxy (MBE) chambers and characterization facilities which allow for an in situ investigation of the crystalline structure by electron diffraction techniques (RHEED and LEED), and of the bulk and surface electronic structure by photoelectron spectroscopy (XPS, ARPES), as well as for in situ temperature-dependent resistivity measurements. Recently, we have developed a growth procedure that makes a controlled deposition of TI thin films and heterostructures with reduced bulk conductivity and tunable surface states feasible. The objective of this project is now to further improve the quality and properties of the films by purposeful choice of substrates and materials and to study changes in the electronic structure induced, for instance, at the interfaces to magnetic or superconducting layers, using in situ angle-resolved photoelectron spectroscopy and electrical transport measurements. We are looking for a PhD student with background in solid state physics and hands-on lab experience, who is also interested in developing new experimental measurement tools.