Following the first experimental realization of graphene, other ultrathin materials with unprecedented electronic properties have been explored, with particular attention given to the heavy group-IV elements Si, Ge and Sn. Two-dimensional buckled Si-based silicene has been recently realized by molecular beam epitaxy growth, whereas Ge-based germanene was obtained by molecular beam epitaxy and mechanical exfoliation. However, the synthesis of Sn-based stanene has proved challenging so far. Here, we report the successful fabrication of 2D stanene by molecular beam epitaxy, confirmed by atomic and electronic characterization using scanning tunnelling microscopy and angle-resolved photoemission spectroscopy, in combination with first-principles calculations. The synthesis of stanene and its derivatives will stimulate further experimental investigation of their theoretically predicted properties, such as a 2D topological insulating behaviour with a very large bandgap, and the capability to support enhanced thermoelectric performance, topological superconductivity and the near-room-temperature quantum anomalous Hall effect.

The surface of a topological insulator plays host to an odd number of linearly-dispersing Dirac fermions, protected against back-scattering by time-reversal symmetry. such characteristics make these materials attractive not only for studying a range of fundamental phenomena in both condensed matter and particle physics, but also for applications ranging from spintronics to quantum computation. Here, we show that the single Dirac cone comprising the topological state of the prototypical topological insulator Bi 2 se 3 can co-exist with a two-dimensional electron gas (2DEG), a cornerstone of conventional electronics. Creation of the 2DEG is tied to a surface band-bending effect, which should be general for narrow-gap topological insulators. This leads to the unique situation where a topological and a non-topological, easily tunable and potentially superconducting, metallic state are confined to the same region of space.

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Majorana fermion (MF) whose antiparticle is itself has been predicted in condensed matter systems. Signatures of the MFs have been reported as zero energy modes in various systems. More definitive evidences associated with MF's novel properties are highly desired to verify the existence of the MF. Very recently, theory has predicted MFs to induce spin selective Andreev reflection (SSAR), a novel magnetic property which can be used to detect the MFs. Here we report the first observation of the SSAR from MFs inside vortices in Bi 2 Te 3 /NbSe 2 hetero-structure, in which topological superconductivity was previously established. By using spin-polarized scanning tunneling

We report a Rashba spin splitting of a two-dimensional electron gas in the topological insulator Bi(2)Se(3) from angle-resolved photoemission spectroscopy. We further demonstrate its electrostatic control, and show that spin splittings can be achieved which are at least an order-of-magnitude larger than in other semiconductors. Together these results show promise for the miniaturization of spintronic devices to the nanoscale and their operation at room temperature.

Using angle-resolved photoelectron spectroscopy and ab-initio GW calculations, we unambiguously show that the widely investigated three-dimensional topological insulator Bi2Se3 has a direct band gap at the Γ point. Experimentally, this is shown by a three-dimensional band mapping in large fractions of the Brillouin zone. Theoretically, we demonstrate that the valence band maximum is located at the Γ point only if many-body effects are included in the calculation. Otherwise, it is found in a high-symmetry mirror plane away from the zone center. PACS numbers: 71.15.m, 71.20.b, 71.70.Ej, Bismuth selenide has been widely studied for many years for its potential applications in optical recording systems [1], photoelectrochemical [2] and thermoelectric devices [3,4], and is nowadays commonly used in refrigeration and power generation. Recently, it has attracted increasing interest after its identification as a prototypical topological insulator (TI) [5,6]. Its surface electronic structure consists of a single Dirac cone around the surface Brillouin zone (SBZ) centreΓ, with the Dirac point (DP) placed closely above the bulk valence band states. In order to exploit the multitude of interesting phenomena associated with the topological surface states [7,8], it is necessary to access the topological transport regime, in which the chemical potential is near the DP and simultaneously in the absolute bulk band gap. Due to the close proximity of the DP and the bulk valence states at Γ, this is only possible if there are no other valence states in Bi 2 Se 3 with energies close to or higher than the DP. Therefore, it is crucial to establish if the bulk valence band maximum (VBM) in bismuth selenide is placed at Γ (and thus projected out toΓ) or at some other position within the Brillouin zone (BZ). As the bulk conduction band minimum (CBM) is undisputedly located at Γ [9,10], the question about the VBM location is identical to the question about the nature of the fundamental band gap in this TI, direct or indirect.The nature of the bulk band gap is thus of crucial importance for the possibility of exploiting the topological surface states in transport, but the position of the VBM in band structure calculations remains disputed. In a linearized muffin-tin orbital method (LMTO) calculation within the local density approximation (LDA), the VBM was found at the Γ point, implying that Bi 2 Se 3 is a direct-gap semiconductor [11]. Contrarily, by employing the full-potential linearized augmented-plane-wave method (FLAPW) within the generalized gradient approximation (GGA), the authors of Ref. 9 have found the VBM to be located on the Z − F line of the BZ, which is lying in the mirror plane. Similar results have been obtained in Ref. 12 with the plane-wave pseudopotential method (PWP) within the LDA. Various density functional theory (DFT) calculations of the surface band structure of Bi 2 Se 3 [5,7,13,14] also indicate that the VBM of bulk bismuth selenide is not located at the BZ center. The inclusion of many-body effects within the G...

The electron dynamics of the topological surface state on Bi2Se3(111) is investigated by temperature-dependent angle-resolved photoemission. The electron-phonon coupling strength is determined in a spectral region for which only intraband scattering involving the topological surface band is possible. The electron-phonon coupling constant is found to be λ = 0.25(5), more than an order of magnitude higher than the corresponding value for intraband scattering in the noble metal surface states. The stability of the topological state with respect to surface irregularities was also tested by introducing a small concentration of surface defects via ion bombardment. It is found that, in contrast to the bulk states, the topological state can no longer be observed in the photoemission spectra and this cannot merely be attributed to surface defect-induced momentum broadening. PACS numbers: 73.20.At,71.70.Ej, Topological insulators are one of of the most intriguing subjects of current condensed matter physics [1-3]. Despite of their insulating bulk, these materials support metallic edge and surface states with an unconventional spin texture [4,5], electron dynamics [6, 7] and stability. Exploiting these properties is the key to several applications, e. g. in spintronics and quantum computing. Moreover, several novel physical phenomena are predicted in connection with the topological states [8-10].The stable existence of a gap-closing surface state [11][12][13] is a property derived from the bulk band structure of a topological insulator, rather than a mere coincidence. The topological state is also stable in a dynamical sense. A hallmark is the absence of back-scattering near nonmagnetic defects. Edge states in the quantum spin Hall effect, a two-dimensional topological insulator, are completely protected from (elastic) scattering [11] whereas the scattering phase space is strongly reduced for surface states on a three dimensional topological insulator [7,14], preventing localization by weak disorder.The stability of the topological state is essential for many phenomena and applications, however, only a few experimental studies have addressed this issue. Experimental measurements using angle resolved photoemission spectroscopy (ARPES) and scanning tunnelling microscopy (STM) have shown that the topological surface states are robust against a small number of adsorbates [15,16] and detectable at room temperature [15], but other results question their stability with respect to surface scattering processes [17]. Here we determine the electron-phonon (el − ph) coupling strength on the topological insulator Bi 2 Se 3 (111) [18,19]. In the absence of defects, el−ph scattering can be expected to be the dominant scattering mechanism at finite temperature and it is therefore of exceptional importance for any application.We concentrate on the spectral region in which only the topological state exists and thus only intraband scattering is possible and we show that while the el − ph coupling constant λ is of moderate size, it is surprisi...

Angle-resolved photoelectron spectroscopy is used for a detailed study of the electronic structure of the topological insulator Bi 2 Se 3 . Nominally stoichiometric and calcium-doped samples were investigated. The pristine surface shows the topological surface state in the bulk band gap. As time passes, the Dirac point moves to higher binding energies, indicating an increasingly strong downward bending of the bands near the surface. This time-dependent band bending is related to a contamination of the surface and can be accelerated by intentionally exposing the surface to carbon monoxide and other species. For a sufficiently strong band bending, additional states appear at the Fermi level. These are interpreted as quantised conduction band states. For large band bendings, these states are found to undergo a strong Rashba splitting. The formation of quantum well states is also observed for the valence band states. Different interpretations of similar data are also discussed.