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.

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    • "The carrier mobilities of the both surface Dirac fermions were evaluated by analyzing the SdH oscillations given by the equation (1) to be μ(B F = 8 T) = comparable with those in the previous bulk insulating 3D-TI thin films prepared by mechanical exfoliation[6]and by MBE[37,38]. In order to estimate the cyclotron mass m, temperature dependence of the amplitude of SdH oscillations was analyzed by the following equation ∆í µí±… í µí±¥í µí±¥ ∝ í µí»¼T ∆E N (í µí°µ) ⁄ sinh [í µí»¼í µí±‡ ∆í µí°¸íµí°¸í µí± (í µí°µ)] ⁄ (2), where E N = heB/2m * c and  = 2 2 k B with the Landau index of N. For evaluation, we chose the most prominent intense signals with LL indices of N 21T = 3, 3.5, 4 and B F = 21T and N 8T = 2 for B F = 8T, and their fitting results are shown in Fig. 4is the free electron mass, and these values are almost the same as the top data of other reported BSTS single crystals[38].BSTS thin films were epitaxially grown on Fluorophlogopite mica (KMg 3 (AlSi 3 O 10 )F 2 ) by catalyst-free physical vapor deposition using dual tubes in a three– zone furnace under pressure of c.a. 0.1Pa. As-grown BSTS films were exfoliated from mica substrates in a NMD–W 2.38% aqueous solution and transferred on other substrates. "

    Full-text · Article · Jan 2016
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    • "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]. "
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    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.
    Full-text · Article · Aug 2015
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    • "Nevertheless, the technique is very sensitive to relatively weak vibrations, and careful design is typically needed to ensure vibration isolation [2]. One of the most important STM applications is imaging in strong magnetic fields, which is crucial for the study of high-temperature superconductors [3] [4] [5] [6], the Dirac nature of the surface states of topological insulators [7] [8] [9], the quantum Hall effect in low-dimensional materials [10] [11], and the vortex formation in quantum dots [12]. To this end, the microscope is routinely housed in a superconducting magnet, which has the advantage of tranquility [13] [14] [15] [16]. "
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    ABSTRACT: We report the achievement of the first atomically resolved scanning tunneling microscope (STM) imaging in a water-cooled magnet (WM), where the extremely harsh vibrations and noises have been the major challenge. This homebuilt WM-STM features an ultra-rigid and compact scan head in which the coarse approach is driven by our new design of the TunaDrive piezoelectric motor. A three-level spring hanging system is exploited for vibration isolation. Room-temperature raw-data images of graphite with quality atomic resolution were obtained in very high magnetic fields up to 27 T in a 32 mm bore WM whose absolute maximum field is 27.5 T at the power rating of 10 MW. This record of 27 T has exceeded the maximum field strength of the conventional superconducting magnets. Besides, our WM-STM has also paved the way to the STM imaging in the 45 T, 32 mm bore hybrid magnet, which is the world's flagship magnet and can produces the highest steady magnetic field at present.
    Full-text · Article · May 2015 · Nano Research
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