Search

Hybrid organic/inorganic interfaceshave been widely reported tohost emergent properties that go beyond those of their single constituents.Coupling molecules to the recently discovered topological insulators,which possess linearly dispersing and spin-momentum-locked Dirac fermions,may offer a promising platform toward new functionalities. Here, wereport a scanning tunneling microscopy and spectroscopy study of theprototypical interface between MnPc molecules and a Bi2Te3surface. MnPc is found to bind stably to the substratethrough its central Mn atom. The adsorption process is only accompaniedby a minor charge transfer across the interface, resulting in a moderatelyn-doped Bi2Te3surface. More remarkably, topologicalstates remain completely unaffected by the presence of the molecules,as evidenced by the absence of scattering patterns around adsorptionsites. Interestingly, we show that, while the HOMO and LUMO orbitalsclosely resemble those of MnPc in the gas phase, a new hybrid stateemerges through interaction with the substrate. Our results pave theway toward hybrid organic–topological insulator heterostructures,which may unveil a broad range of exciting and unknown phenomena. [ABSTRACT FROM AUTHOR]

The binary chalcogenides Bi2Te3 and Bi2Se3 are the most widely studied topological insulators. Although the quantum anomalous Hall effect has recently been observed in magnetically doped Sb2Te3, this compound has been studied to a much lesser extent. Here, by using energy-resolved quasiparticle interference mapping, we investigate the scattering events of pristine Sb2Te3 surfaces. We find that, in addition to the Dirac fermions, another strongly spin-polarized surface resonance emerges at higher energies in the unoccupied electronic states. Although the two surface states are of different origin, i.e., topologically protected and trivial, respectively, both show strongly directional scattering properties and absence of backscattering. A comparison with ab initio calculations demonstrates that this is a direct consequence of their spin-momentum-locked spin texture which is found to exhibit an opposite rotational sense for the trivial state and the Dirac state. [ABSTRACT FROM AUTHOR]

We performed a scanning tunneling spectroscopy investigation of the electronic properties of the topological insulator Bi2Te3 in the energy range between -200 and +700 meV with respect to the Fermi level. For unoccupied states, tunneling into topological surface states dominates. Analysis of Fourier-transformed (FT) dI/dU maps allowed us to obtain their energy dispersion relation and to visualize the breakdown of the linear dispersion relation typical of massless particles. For occupied states, no signature of scattering events involving surface states can be detected. FT dI/dU maps reveal in this case two scattering vectors pointing along the ΓM and ΓK directions. Both are identified with scattering events within bulk states. Interestingly, vectors pointing along ΓK which correspond to bulk backscattering events have a length longer than the minimum distance necessary to match opposite pockets on a constant energy cut. Comparison with calculated spin-resolved constant-energy cuts shows that this is a direct consequence of the chiral spin texture present in bulk states when their energy and momentum are close to the resonances of the spin-polarized topological surface states. [ABSTRACT FROM AUTHOR]

Topological crystalline insulators are materials in which the crystalline symmetry leads to topologically protected surface states with a chiral spin texture, rendering them potential candidates for spintronics applications. Using scanning tunneling spectroscopy, we uncover the existence of one-dimensional (1D) midgap states at odd-atomic surface step edges of the three-dimensional topological crystalline insulator (Pb,Sn)Se. A minimal toy model and realistic tight-binding calculations identify them as spin-polarized flat bands connecting two Dirac points. This nontrivial origin provides the 1D midgap states with inherent stability and protects them from backscattering. We experimentally show that this stability results in a striking robustness to defects, strong magnetic fields, and elevated temperature., (Copyright © 2016, American Association for the Advancement of Science.)

The effective gating of topological insulators is demonstrated, through the coupling of molecules to their surface. By using electric fields, they allow for dynamic control of the interface charge state by adding or removing single electrons. This process creates a robust transconductance bistability resembling a single-electron transistor. These findings make hybrid molecule/topological interfaces functional elements while at the same time pushing miniaturization to its ultimate limit., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Topological insulators interacting with magnetic impurities have been reported to host several unconventional effects. These phenomena are described within the framework of gapping Dirac quasiparticles due to broken time-reversal symmetry. However, the overwhelming majority of studies demonstrate the presence of a finite density of states near the Dirac point even once topological insulators become magnetic. Here, we map the response of topological states to magnetic impurities at the atomic scale. We demonstrate that magnetic order and gapless states can coexist. We show how this is the result of the delicate balance between two opposite trends, that is, gap opening and emergence of a Dirac node impurity band, both induced by the magnetic dopants. Our results evidence a more intricate and rich scenario with respect to the once generally assumed, showing how different electronic and magnetic states may be generated and controlled in this fascinating class of materials.

A Bi2Te3 single crystal is grown with the modified Bridgman technique. The crystal has a nominal composition with a Te content of 61 mol% resulting in the existence of two distinct regions, p- and n-doped, respectively; color-coded tunneling spectra are taken over 60 nm at the transition region., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Quantum interference is a striking manifestation of one of the basic concepts of quantum mechanics: the particle-wave duality. A spectacular visualization of this effect is the standing wave pattern produced by elastic scattering of surface electrons around defects, which corresponds to a modulation of the electronic local density of states and can be imaged using a scanning tunnelling microscope. To date, quantum-interference measurements were mainly interpreted in terms of interfering electrons or holes of the underlying band-structure description. Here, by imaging energy-dependent standing-wave patterns at noble metal surfaces, we reveal, in addition to the conventional surface-state band, the existence of an 'anomalous' energy band with a well-defined dispersion. Its origin is explained by the presence of a satellite in the structure of the many-body spectral function, which is related to the acoustic surface plasmon. Visualizing the corresponding charge oscillations provides thus direct access to many-body interactions at the atomic scale.

The spin-momentum locking of topological states offers an ideal platform to explore novel magnetoelectric effects. These intimately depend on the ability to manipulate the spin texture in a controlled way. Here we combine scanning tunnelling microscopy with single-atom deposition to map the evolution of topological states under the influence of different magnetic perturbations. We obtain signatures of Dirac fermion-mediated magnetic order for extremely dilute adatom concentrations. This striking observation is found to critically depend on the single adatoms' magnetic anisotropy and the position of the Fermi level. Our findings open new perspectives in spin engineering topological states at the atomic scale and pave the way to explore novel spin-related topological phenomena with promising potential for applications.