Fermiology of possible topological superconductor ${\mathrm{Tl}}_{0.5}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ derived from hole-doped topological insulator

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Fermiology of possible topological superconductor ${Tl}_{0.5} {Bi}_{2} {Te}_{3}$ derived from hole-doped topological insulator

C. X. Trang, Z. Wang, D. Takane, K. Nakayama, S. Souma, T. Sato, T. Takahashi, A. A. Taskin, and Yoichi Ando

Phys. Rev. B 93, 241103(R) – Published 13 June 2016

Abstract

We have performed angle-resolved photoemission spectroscopy on ${Tl}_{0.5} {Bi}_{2} {Te}_{3}$ , a possible topological superconductor derived from ${Bi}_{2} {Te}_{3}$ . We found that the bulk Fermi surface consists of multiple three-dimensional hole pockets surrounding the Z point, produced by the direct hole doping into the valence band. The Dirac-cone surface state is well isolated from the bulk bands, and the surface chemical potential is variable in the entire band-gap range. ${Tl}_{0.5} {Bi}_{2} {Te}_{3}$ thus provides an excellent platform to realize two-dimensional topological superconductivity through a proximity effect from the superconducting bulk. Also, the observed Fermi-surface topology provides a concrete basis for constructing theoretical models for bulk topological superconductivity in hole-doped topological insulators.

Received 12 April 2016

DOI:https://doi.org/10.1103/PhysRevB.93.241103

Physics Subject Headings (PhySH)

Fermi surface

Topological superconductors

Angle-resolved photoemission spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

C. X. Trang¹, Z. Wang², D. Takane¹, K. Nakayama¹, S. Souma³, T. Sato¹, T. Takahashi^1,3, A. A. Taskin², and Yoichi Ando²

¹Department of Physics, Tohoku University, Sendai 980-8578, Japan
²Institute of Physics II, University of Cologne, Köln 50937, Germany
³WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan

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Vol. 93, Iss. 24 — 15 June 2016

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Figure 1
(a) Bulk rhombohedral BZ (red) and corresponding hexagonal surface BZ (blue) of ${Tl}_{0.5} {Bi}_{2} {Te}_{3}$ . Green shaded area indicates the $k_{x} − k_{z}$ plane. (b) Plot of ARPES intensity in the VB region as a function of the in-plane wave vector and $E_{B}$ , measured at $h ν = 21$ eV at $T = 40$ K. (c) Bulk BZ in the $k_{x} − k_{z}$ plane together with measured cuts for $h ν = 15$ and 21 eV (blue and black curves). $k_{z}$ values were calculated with the inner potential $V_{0}$ of 12 eV which was estimated from the periodicity of bands in (d). (d) Photon-energy dependence of the normal-emission EDCs near $E_{F}$ . (e) Plot of ARPES intensity as a function of $k_{z}$ and $E_{B}$ . The location of $Γ$ and Z points in bulk BZ is indicated by dashed lines.
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Figure 2
(a) ARPES-intensity mapping at $E_{F}$ as a function of the 2D wave vector $(k_{x} − k_{y})$ measured at $h ν = 21$ eV. Yellow lines indicate the measured k cuts. (b) ARPES-intensity mapping for various $E_{B}$ 's between 0.1 and 0.5 eV. (c)–(e) Near- $E_{F}$ ARPES intensity as a function of the in-plane wave vector and $E_{B}$ measured along representative k cuts (A–C) shown in (a). (f) Calculated band structure along the $\bar{Γ} \bar{M}$ cut obtained from the first-principles band calculations of bulk ${Bi}_{2} {Te}_{3}$ for various $k_{z}$ 's. In order to take into account the hole-doping effect, the energy position of $E_{F}$ was set to be 70 meV below the VB top in the calculation. Band dispersions centered at $k_{z} = 0.9 π$ are shown by red curves; gradual shading highlights the $k_{z}$ broadening of the $\pm 0.1 π$ window. (g) 3D view of a schematic FS around the Z point, constructed from the band calculations of hole-doped ${Bi}_{2} {Te}_{3}$ with the $E_{F}$ position at 70 meV below the VB top. Yellow and red colors on the FS correspond to portions for $k_{z} < 0.9 π$ and $k_{z} > 0.9 π$ , respectively.
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Figure 3
(a), (b) Near- $E_{F}$ ARPES intensity just after cleaving (fresh), measured along cut D in Fig. 2 at $h ν = 15$ and 21 eV, respectively. $k$ cuts at $h ν = 15$ and 21 eV nearly cross the $Γ$ and Z points of bulk BZ, respectively, as shown in Fig. 1. VB and SS denote the valence band and surface state, respectively. (c), (d) The same as (a) and (b) but 12 h after cleaving (aged). CB denotes the conduction band. (e) Dirac-cone band dispersion relative to the Dirac point (DP) for fresh and aged surfaces of ${Tl}_{0.5} {Bi}_{2} {Te}_{3}$ . The energy position of the chemical potential $μ$ for each sample is indicated by a horizontal dashed line. The band dispersion was estimated from the numerical fittings of the momentum distribution curves for (a)–(d).
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Figure 4
Comparison of the schematic FS (top) and the band diagram (bottom) between (a) ${Tl}_{x} {Bi}_{2} {Te}_{3}$ and (b) ${Cu}_{x} {Bi}_{2} {Se}_{3}$ .
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Physical Review B

covering condensed matter and materials physics

Fermiology of possible topological superconductor ${Tl}_{0.5} {Bi}_{2} {Te}_{3}$ derived from hole-doped topological insulator

C. X. Trang, Z. Wang, D. Takane, K. Nakayama, S. Souma, T. Sato, T. Takahashi, A. A. Taskin, and Yoichi Ando

Phys. Rev. B 93, 241103(R) – Published 13 June 2016

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Physical Review B

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Fermiology of possible topological superconductor Tl0.5Bi2Te3 derived from hole-doped topological insulator

C. X. Trang, Z. Wang, D. Takane, K. Nakayama, S. Souma, T. Sato, T. Takahashi, A. A. Taskin, and Yoichi Ando

Phys. Rev. B 93, 241103(R) – Published 13 June 2016

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Fermiology of possible topological superconductor ${Tl}_{0.5} {Bi}_{2} {Te}_{3}$ derived from hole-doped topological insulator