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Two-dimensional honeycomb crystals have inspired intense research interest for their novel properties and great potential in electronics and optoelectronics. Here, through molecular beam epitaxy on SrTiO3(001), we report successful epitaxial growth of metal-rich chalcogenide Fe2Te, a honeycomb-structured film that has no direct bulk analogue, under Te-limited growth conditions. The structural morphology and electronic properties of Fe2Te are explored with scanning tunneling microscopy and angle resolved photoemission spectroscopy, which reveal electronic bands cross the Fermi level and nearly flat bands. Moreover, we find a weak interfacial interaction between Fe2Te and the underlying substrates, paving a newly developed alternative avenue for honeycomb-based electronic devices. [ABSTRACT FROM AUTHOR]

We report transport measurements on Josephson junctions consisting of Bi2Te3 topological insulator (TI) thin films contacted by superconducting Nb electrodes. For a device with junction length L = 134 nm, the critical supercurrent Ic can be modulated by an electrical gate which tunes the carrier type and density of the TI film. Ic can reach a minimum when the TI is near the charge neutrality regime with the Fermi energy lying close to the Dirac point of the surface state. In the p-type regime the Josephson current can be well described by a short ballistic junction model. In the n-type regime the junction is ballistic at 0.7 K < T < 3.8 K while for T < 0.7 K the diffusive bulk modes emerge and contribute a larger Ic than the ballistic model. We attribute the lack of diffusive bulk modes in the p-type regime to the formation of p–n junctions. Our work provides new clues for search of Majorana zero mode in TI-based superconducting devices. [ABSTRACT FROM AUTHOR]

Interface superconductivity, realized in multiple artificial crystalline heterostructures, is one of the most exciting directions to search for high-temperature superconductivity. In this work, we prepare bulk (FeSe)η(SrTiO3)1−η multi-grain composites by a simple facile liquid-phase compaction method using a spark-plasma-sintering technique. Combining transmission electron microscopy/scanning electron microscopy and x-ray diffraction investigations, we demonstrate that the composites consist of micron-scale SrTiO3 grains surrounded by [001]-compressed β-FeSe grains. Transport measurements for the composites with FeSe mole fraction η > 0.06 reveal that two superconducting channels, one Tc ∼ 13 K phase from FeSe/SrTiO3 interfaces and another Tc ∼ 7 K phase from FeSe grains, cooperatively induce macroscopic superconducting behavior with isotropic upper critical fields above 40 T. This work points out a straightforward method to enhance Tc in the multi-grain (FeSe)η(SrTiO3)1−η composites by reducing the crystalline grains to nanoscale and finely tuning the stoichiometries of FeSe and SrTiO3. [ABSTRACT FROM AUTHOR]

Quantum Hall effect (QHE), as a class of quantum phenomena that occur in macroscopic scale, is one of the most important topics in condensed matter physics. It has long been expected that QHE may occur without Landau levels so that neither external magnetic field nor high sample mobility is required for its study and application. Such a QHE free of Landau levels, can appear in topological insulators (TIs) with ferromagnetism as the quantized version of the anomalous Hall effect, i.e., quantum anomalous Hall (QAH) effect. Here we review our recent work on experimental realization of the QAH effect in magnetically doped TIs. With molecular beam epitaxy, we prepare thin films of Cr-doped (Bi,Sb)2Te3 TIs with well-controlled chemical potential and long-range ferromagnetic order that can survive the insulating phase. In such thin films, we eventually observed the quantization of the Hall resistance at h/e² at zero field, accompanied by a considerable drop in the longitudinal resistance. Under a strong magnetic field, the longitudinal resistance vanishes, whereas the Hall resistance remains at the quantized value. The realization of the QAH effect provides a foundation for many other novel quantum phenomena predicted in TIs, and opens a route to practical applications of quantum Hall physics in low-power-consumption electronics. [ABSTRACT FROM AUTHOR]

We report high transition temperature superconductivity in one unit-cell (UC) thick FeSe films grown on a Seetched SrTiO3(001) substrate by molecular beam epitaxy (MBE). A superconducting gap as large as 20 meV and the magnetic field induced vortex state revealed by in situ scanning tunneling microscopy (STM) suggest that the superconductivity of the 1 UC FeSe films could occur around 77 K. The control transport measurement shows that the onset superconductivity temperature is well above 50 K. Our work not only demonstrates a powerful way for finding new superconductors and for raising TC, but also provides a well-defined platform for systematic studies of the mechanism of unconventional superconductivity by using different superconducting materials and substrates. [ABSTRACT FROM AUTHOR]

We perform molecular beam epitaxy growth and scanning tunneling microscopy study of copper diselenide (CuSe2) films on SrTiO3(001). Using a Se-rich condition, the single-phase pyrite CuSe2 grows in the Stranski—Krastanov (layer-plus-island) mode with a preferential orientation of (111). Our careful inspection of both the as-grown and post-annealed CuSe2 films at various temperatures invariably shows a Cu-terminated surface, which, depending on the annealing temperature, reconstructs into two distinct structures and . The Cu termination is supported by the depressed density of states near the Fermi level, measured by in-situ low temperature scanning tunneling spectroscopy. Our study helps understand the preparation and surface chemistry of transition metal pyrite dichalcogenides thin films. [ABSTRACT FROM AUTHOR]

Atomically flat thin films of topological semimetal Na3 Bi are grown on double-layer graphene formed on 6H–SiC(0001) substrates by molecular beam epitaxy. By combined techniques of molecular beam epitaxy, scanning tunneling microscopy and angle resolved photoelectron spectroscopy, the growth conditions for Na3 Bi thin films on double-layer graphene are successfully established. The band structure of Na3 Bi grown on graphene is mapped along Γ̄–M̄ and Γ̄–K̄ directions. Furthermore, the energy band of Na3 Bi at higher energy is uncovered by doping Cs atoms on the surface. [ABSTRACT FROM AUTHOR]