Research 1:Topological insulators & nanostructured graphene
Protection from Electron Backscattering in Topological Insulator
The elasticscattering vector within topological surface states (TSS) of a topological insulator Bi_{1.5}Sb_{0.5}Te_{1.7}Se_{1.3} was obtained on the cleaved surface from a quasiparticle interference pattern, which is a Fouriertransformed constantvoltage dI/dV image measured using STM at 5 K. The observed elastic scattering amplitude within the TSS was critically suppressed beyond certain scatteringvector lengths (CSLs). The band dispersion, which was measured by using angleresolved photoemission spectroscopy implemented by a pumpandprobe method, is compared with the CSLs. The scattering in the TSS is effectively prohibited in a wide angular range of 100180^{o}. (details) .
(left) STM image (a), dI/dV image (b), FFT images (c,d) of a cleaved surface of BiSbTeSe. (right) (a,b) band dispersion of TSS studied by pumpandprobe ARPES. (c,d) Large angle scatterings are prohibited.
Scanning tunneling spectroscopy study of quasiparticle interference on dual
topological insulator Bi_{1x}Sb_{x}
Electronic states of the topological insulator Bi_{1x}Sb_{x}, which is nontrivial in terms of both the Z_{2} index and the mirror Chern number, were studied by quasiparticle interference (QPI) using lowtemperature scanning tunneling spectroscopy.
Our Fouriertransform analysis of the QPI patterns reveals the dispersion of the two surface bands above the Fermi energy.
Absence of the surface band crossing is unambiguously confirmed, which allowed us to elucidate the mirror Chern number of this system is 1.
(details) .
(left) STM image (a), dI/dV curve (b), dI/dV image (c), FFT images (d) of a cleaved surface of Bi_{1x}Sb_{x}. (right) (ad) Fourietransformation (FT) of dI/dV
maps at E = 140 (a), 40 (b), +160 (c), and +260(d) meV, (e) FT image in the GM and
GK directions. (f) Scattering vectors, (g) Surface band structure.
Spatiallydependent inelastic tunneling spectroscopy of nanorippled graphene on a vicinal SiC(0001)
Nanorippled graphene is grown on a macrofacet of SiC(0001) by thermal decomposition. The period of the ripple is confirmed by LEED, STM and replica structure of graphene piband ARPES. Inelastic tunneling signals due to graphene phonon excitation modulate according to the period of graphene nanoripple. Presence of graphene nanoribbons at the interface between the surface nanorippled graphene and SiC macrofacet is suggested.
(left) (a) LEED and (b,c) ARPES results at K, (right) (a,b) STM images and (c) inelastic tunneling spectra (d) hight profile, for nanorippled graphene on a macrofacet of SiC(0001).
Graphene nanoribbons on a vicinal SiC(0001)
Graphene nanoribbons (GNR) are grown by molecular beam epitaxy on vicinal SiC(0001) substrates, and their electronic structure is studied by ARPES. GNR with armchair edges parallel to the step edge of the substrate covers the terraces of 520 nm wide substrate of stepandterrace structure. The graphene Dirac band shows a bandgap at Kpoints, the gap size increase with decreasing the ribbon width. (details) .
AFM image and the results of ARPES at K for graphene nanoribbon on a 4degreeoff SiC(0001).
Graphene on a vicinal SiC(0001)
Electronic structure of singlelayer graphene grown on a vicinal SiC(0001) is studied. Graphene covers the whole substrate of stepandterrace structure, and is curved over the step edges. The curved areas induces the scattering of the Dirac electrons as observed in the line width of ARPES (details) . Owing to the electron scattering, the graphene Dirac band on the terrace is elongated in the direction perpendicular to the step edges as observed by ARPES (details) .
STM images and the results of ARPES for graphene on a 4degreeoff SiC(0001)
STM images of graphene on an 8degreeoff vicinal SiC(0001), and cone shapes of the graphene Dirac band at Fermi energy.
Institute for Solid State Physics , University of Tokyo
Kashiwanoha, Kashiwashi, Chiba 2778581, Japan
Tel +81 471363310 / FAX +81 471363474
Last update: 2017/9/1 by komori(AT)issp.utokyo.ac.jp
