Observation of Dirac Holes and Electrons in a Topological Insulator

Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Japan.
Physical Review Letters (Impact Factor: 7.51). 07/2011; 107(1):016801. DOI: 10.1103/PhysRevLett.107.016801
Source: PubMed


We show that in the new topological-insulator compound Bi(1.5)Sb(0.5)Te(1.7)Se(1.3) one can achieve a surfaced-dominated transport where the surface channel contributes up to 70% of the total conductance. Furthermore, it was found that in this material the transport properties sharply reflect the time dependence of the surface chemical potential, presenting a sign change in the Hall coefficient with time. We demonstrate that such an evolution makes us observe both Dirac holes and electrons on the surface, which allows us to reconstruct the surface band dispersion across the Dirac point.

Download full-text


Available from: Satoshi Sasaki, Oct 08, 2015
23 Reads
  • Source
    • "In BiSbTeSe 2 , the Dirac point nearly coincides with E F , it thus may serve as a benchmark for the bulk carrier dynamics at very low carrier concentrations. For a sample thickness d 10 µm, the bulk conductance of BiSbTeSe 2 is low enough at low temperatures to be out-weighted by the surface conductance [23] [27] [28]. This allows to observe a hallmark of topological transport , the half-integer quantum Hall effect, at temperatures up to 35 K [27]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Three-dimensional topological insulators harbour metallic surface states with exotic properties. In transport or optics, these properties are typically masked by defect-induced bulk carriers. Compensation of donors and acceptors reduces the carrier density, but the bulk resistivity remains disappointingly small. We show that measurements of the optical conductivity in BiSbTeSe$_2$ pinpoint the presence of electron-hole puddles in the bulk at low temperatures, which is essential for understanding DC bulk transport. The puddles arise from large fluctuations of the Coulomb potential of donors and acceptors, even in the case of full compensation. Surprisingly, the number of carriers appearing within puddles drops rapidly with increasing temperature and almost vanishes around 40 K. Monte Carlo simulations show that a highly non-linear screening effect arising from thermally activated carriers destroys the puddles at a temperature scale set by the Coulomb interaction between neighbouring dopants, explaining the experimental observation semi-quantitatively. This mechanism remains valid if donors and acceptors do not compensate perfectly.
  • Source
    • "The single crystals of Bi1.5Sb0.5Te1.7Se1.3, Bi2Se3, and Sn-doped (0.4%) Bi2Te2Se were grown by a Bridgman method in evacuated quartz tubes [5] [6] [7]. 20-nm-thick Ni81Fe19 thin films were deposited in a high vacuum by electron-beam evaporation on cleaved surfaces of TIs. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Detection and manipulation of electrons' spins are key prerequisites for spin-based electronics or spintronics. This is usually achieved by contacting ferromagnets with metals or semiconductors, in which the relaxation of spins due to spin-orbit coupling limits both the efficiency and the length scale. In topological insulator materials, on the contrary, the spin-orbit coupling is so strong that the spin direction uniquely determines the current direction, which allows us to conceive a whole new scheme for spin detection and manipulation. Nevertheless, even the most basic process, the spin injection into a topological insulator from a ferromagnet, has not yet been demonstrated. Here we report successful spin injection into the surface states of topological insulators by using a spin pumping technique. By measuring the voltage that shows up across the samples as a result of spin pumping, we demonstrate that a spin-electricity conversion effect takes place in the surface states of bulk-insulating topological insulators Bi1.5Sb0.5Te1.7Se1.3 and Sn-doped Bi2Te2Se. In this process, due to the two-dimensional nature of the surface state, there is no spin current along the perpendicular direction. Hence, the mechanism of this phenomenon is different from the inverse spin Hall effect and even predicts perfect conversion between spin and electricity at room temperature. The present results reveal a great advantage of topological insulators as inborn spintronics devices.
  • Source
    • "However, finding unambiguous evidence of the surface states using transport experiments has proven to be difficult. Namely, in most TI samples charge transport is dominated by a high bulk conductivity due to residual carriers arising from self-doping by point defects in the material, which complicates the identification of the surface contribution to the conductivity [7] [8] [9]. So far, successful approaches to suppressing the bulk conductivity include chemical doping [8], electrical gating [10] or the increase of the surfaceto-volume ratio by fabricating thin films or nanowires [11]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Electron irradiation is investigated as a way to dope the topological insulator Bi_{2}Te_{3}. For this, p-type Bi_{2}Te_{3} single crystals have been irradiated with 2.5 MeV electrons at room temperature and electrical measurements have been performed in situ as well as ex situ in magnetic fields up to 14 T. The defects created by irradiation act as electron donors, allowing the compensation of the initial hole-type conductivity of the material as well as the conversion of the conductivity from p to n type. The changes in carrier concentration are investigated using the Hall effect and Shubnikov–de Haas (SdH) oscillations, clearly observable in the p-type samples before irradiation, but also after the irradiation-induced conversion of the conductivity to n type. The SdH patterns observed for the magnetic field along the trigonal axis can be entirely explained assuming the contributions of only one valence and one conduction band, respectively, and Zeeman splitting of the orbital levels.
    Physical Review B 11/2013; 88(20). DOI:10.1103/PhysRevB.88.205207 · 3.74 Impact Factor
Show more