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.

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.

a high conductivity of 0.46 mS cm −1 at room temperature because the three-dimensional pathways in the open framework benefi t the diffusion of Na ions. [ 5 ] Further improvement (60%, 0.74 mS cm −1 ) has been obtained by substitution of Si on P sites in 94Na 3 PS 4 -6Na 4 SiS 4 . [ 6 ] However, the ionic conductivity is still low in comparison to liquid electrolytes, and therefore SEs with higher ionic conductivity need to be sought.Tatsumisago and co-workers found that an appropriate diffusion channel size is critical for fast ion diffusion and anion substitutions have a greater effect on ionic diffusivity than cation substitutions. [ 7 ] Moreover, Se-substituted lithium sulfi des demonstrate an enhanced ionic conductivity in comparison with their pristine compounds. [ 8 ] The advantages of Se-doping lie in two aspects. On one hand, the atomic radius of Se is bigger than that of S, so Se substitution on S sites may expand the lattice. On the other hand, the higher polarizability of Se 2− may weaken the binding energy between the moving ion and the anion framework. These modifi cations may be benefi cial for Na + diffusion because of the big ionic radius of sodium. It is therefore highly interesting to synthesize Na 3 PSe 4 and evaluate its electrochemical performance.In this study, cubic Na 3 PSe 4 was synthesized for the fi rst time and its crystal structure, spectra, and electrochemical performance were investigated. A ionic conductivity of 1.16 mS cm −1 was observed; to the best of our knowledge, this is one of the best values among sodium ion conductors and is the highest value reported for sulfi des to date. Figure 1 a shows the X-Ray Diffraction (XRD) pattern of Na 3 PSe 4 . The halo patterns in both cases refl ect the polyimide fi lm. The crystal structure of Na 3 PSe 4 has not been reported yet. Here, the integrated intensities from powder XRD data were extracted by the Le Bail method using the FullProf program. The crystal structure was solved by using the direct space method and was then refi ned by the Rietveld method. The crystal structure was determined to be cubic with the space group I -43 m (No. 217) and Z = 2. The plots of the observed, calculated, and difference patterns from the Rietveld refi nement (Figure 1 a) evidence the formation of single-phase Na 3 PSe 4 . The refi ned crystallographic data are listed in Table 1 . The cell has a lattice parameter a = 7.3094(2) Å, which is much larger than that of Si-doped Na 3 PS 4 ( a = 6.9978 Å). [ 6 ] A negative isotropic atomic displacement parameter ( U iso ) for P atoms and large U iso values for Na and Se atoms are obtained, indicating large disorders in the crystal structure. Comparison of the XRD patterns of Na 3 PSe 4 before and after ball milling ( Figure S1, Supporting Information) shows that only peak broadening is observed. This observation is in accordance with Differential scanning calorimetry (DSC) results ( Figure S2,The development of large-scale energy-storage system attracts worldwide attention because of the rapidly increasing de...

The robustness of the gapless topological surface state hosted by a 3D topological insulator against perturbations of magnetic origin has been the focus of recent investigations. We present a comprehensive study of the magnetic properties of Fe impurities on a prototypical 3D topological insulator Bi2Se3 using local low temperature scanning tunneling microscopy and integral x-ray magnetic circular dichroism techniques. Single Fe adatoms on the Bi2Se3 surface, in the coverage range ≈ 1% are heavily relaxed into the surface and exhibit a magnetic easy axis within the surface-plane, contrary to what was assumed in recent investigations on the opening of a gap. Using ab initio approaches, we demonstrate that an in-plane easy axis arises from the combination of the crystal field and dynamic hybridization effects.Topological insulators (TI) have demanded heavy interest from the scientific community as a new class of materials illuminating fascinating yet exotic physics and offering large potential for applications in the field of spintronics [1]. TI host a gapless topological surface state (TSS) which exhibits a Dirac-cone like dispersion. However, unlike in the case of graphene, the Dirac cone is located in the center of the Brillouin-zone and the spin and momentum degrees of freedom are locked. The latter so-called topological quality of the TSS is protected by time-reversal symmetry which leads to a variety of interesting effects. For example, these materials may be a forum for Majorana fermions [2], a topological magnetoelectric effect [3], and a quantized anomalous Hall effect [4].The locking of both spin and momentum degrees of freedom leads to the suppression of 180 • elastic backscattering of TSS electrons in the absence of spin-flip processes. The robustness of these "topologically protected" processes, when introducing impurities which break time reversal symmetry, is of critical importance for spinbased transport in such materials. It has been suggested that the interaction between magnetic impurities and the topological state can cause an opening of an energy gap at the Dirac point (DP), provided that the magnetic order is oriented normal to the surface plane [5][6][7]. Nevertheless, the stability of the TSS against local magnetic perturbations is currently under heavy debate [8][9][10], since little is known about the fundamental interface effects of magnetic entities with TI surfaces as well as the static magnetic properties of impurities in these materials.In this work we present a comprehensive study of the magnetic properties of iron impurities on a prototypical TI Bi 2 Se 3 using local scanning tunneling microscopy (STM) and integral x-ray magnetic circular dichroism (XMCD) techniques. We show that the multiplet structure visible in x-ray absorption spectra reflect a high-spin state of the adsorbed Fe impurities, which are confirmed to bind at hollow sites of the surface lattice, under the influence of trigonal crystal fields given in hollow site positions of the Bi 2 Se 3 surface. In contrary to rec...

Exposing the (111) surface of the topological insulator Bi(2)Se(3) to carbon monoxide results in strong shifts of the features observed in angle-resolved photoemission. The behavior is very similar to an often reported "aging" effect of the surface, and it is concluded that this aging is most likely due to the adsorption of rest gas molecules. The spectral changes are also similar to those recently reported in connection with the adsorption of the magnetic adatom Fe. All spectral changes can be explained by a simultaneous confinement of the conduction band and valence band states. This is possible only because of the unusual bulk electronic structure of Bi(2)Se(3). The valence band quantization leads to spectral features which resemble those of a band gap opening at the Dirac point.