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We investigated the Dirac-cone state and its modulation when an ultrathin film of topological insulator Bi2Se3 was epitaxially grown on a van-der-Waals ferromagnet Cr2Si2Te6 (CST) by angle-resolved photoemission spectroscopy. We observed a gapless Dirac-cone surface state in 6 quintuple-layer (QL) Bi2Se3 on CST, whereas the Dirac cone exhibits a gap of 0.37 eV in 2QL counterpart. Intriguingly, this gap is much larger than those for Bi2Se3 films on Si(111). We also revealed no discernible change in the gap magnitude across the ferromagnetic transition of CST, suggesting the very small characteristic length and energy scale of the magnetic proximity effect. The present results suggest a crucial role of interfacial coupling for modulating Dirac electrons in topological-insulator hybrids.

We have performed angle-resolved photoemission spectroscopy on a heterostructure consisting of topological insulator Bi2Te3 and iron chalcogenide FeTe fabricated on SrTiO3 substrate by molecular-beam-epitaxy technique. This system was recently found to show superconductivity albeit non-superconducting nature of each constituent material. Upon interfacing FeTe with two quintuple layers of Bi2Te3, we found that the Dirac-cone surface state of Bi2Te3 is shifted toward higher binding energy, while the holelike band at the Fermi level originating from FeTe moves toward lower binding energy. This suggests that electron charge transfer takes place from FeTe to Bi2Te3 through the interface. The present result points to importance of hole-doped FeTe interface for the occurrence of unconventional superconductivity., Comment: 5 pages, 4 figures

Calcium-intercalated multilayer silicene CaSi2 exhibits a massless Dirac-cone π-electron-band dispersion like graphene, while the Dirac point is about 2 eV away from the Fermi level due to diiimide-based charge transfer from the Ca atoms to the silicene layers. This indicates that the graphene-like electronic structure with a massless Dirac cone is stably formed in the metal-intercalated multilayer silicene.

We report the emergence of a charge-density wave (CDW) in Ca-intercalated bilayer graphene (${\mathrm{C}}_{6}\mathrm{Ca}{\mathrm{C}}_{6}$), the thinnest limit of superconducting ${\mathrm{C}}_{6}\mathrm{Ca}$, observed by low-temperature, high-magnetic-field scanning tunneling microscopy or spectroscopy, and angle-resolved photoemission spectroscopy. While the possible superconductivity was not observed in epitaxially grown ${\mathrm{C}}_{6}\mathrm{Ca}{\mathrm{C}}_{6}$ on a SiC substrate, a CDW order different from that observed on the surface of bulk ${\mathrm{C}}_{6}\mathrm{Ca}$ was observed. It is inferred that the CDW state is induced by the potential modulation due to the commensurate lattice matching between the ${\mathrm{C}}_{6}\mathrm{Ca}{\mathrm{C}}_{6}$ film and the SiC substrate.