43 research outputs found
Emergent quantum confinement at topological insulator surfaces
Bismuth-chalchogenides are model examples of three-dimensional topological
insulators. Their ideal bulk-truncated surface hosts a single spin-helical
surface state, which is the simplest possible surface electronic structure
allowed by their non-trivial topology. They are therefore widely
regarded ideal templates to realize the predicted exotic phenomena and
applications of this topological surface state. However, real surfaces of such
compounds, even if kept in ultra-high vacuum, rapidly develop a much more
complex electronic structure whose origin and properties have proved
controversial. Here, we demonstrate that a conceptually simple model,
implementing a semiconductor-like band bending in a parameter-free
tight-binding supercell calculation, can quantitatively explain the entire
measured hierarchy of electronic states. In combination with circular dichroism
in angle-resolved photoemission (ARPES) experiments, we further uncover a rich
three-dimensional spin texture of this surface electronic system, resulting
from the non-trivial topology of the bulk band structure. Moreover, our study
reveals how the full surface-bulk connectivity in topological insulators is
modified by quantum confinement.Comment: 9 pages, including supplementary information, 4+4 figures. A high
resolution version is available at
http://www.st-andrews.ac.uk/~pdk6/pub_files/TI_quant_conf_high_res.pd
Emergence of non-centrosymmetric topological insulating phase in BiTeI under pressure
The spin-orbit interaction affects the electronic structure of solids in
various ways. Topological insulators are one example where the spin-orbit
interaction leads the bulk bands to have a non-trivial topology, observable as
gapless surface or edge states. Another example is the Rashba effect, which
lifts the electron-spin degeneracy as a consequence of spin-orbit interaction
under broken inversion symmetry. It is of particular importance to know how
these two effects, i.e. the non-trivial topology of electronic states and
Rashba spin splitting, interplay with each other. Here we show, through
sophisticated first-principles calculations, that BiTeI, a giant bulk Rashba
semiconductor, turns into a topological insulator under a reasonable pressure.
This material is shown to exhibit several unique features such as, a highly
pressure-tunable giant Rashba spin splitting, an unusual pressure-induced
quantum phase transition, and more importantly the formation of strikingly
different Dirac surface states at opposite sides of the material.Comment: 5 figures are include
On the understanding of current-induced spin polarization of three-dimensional topological insulators
Quantum Oscillation Signatures of Pressure-induced Topological Phase Transition in BiTeI
Zeeman-type spin splitting controlled by an electric field
Transition-metal dichalcogenides such as WSe2 and MoS2 have electronic band structures that are ideal for hosting many exotic spin–orbit phenomena. Here we investigate the possibility to generate and modulate a giant Zeeman-type spin polarization in WSe2 under an external electric field. By tuning the perpendicular electric field applied to the WSe2 channel with an electric-double-layer transistor, we observe a systematic crossover from weak localization to weak anti-localization in magnetotransport. Our optical reflection measurements also reveal an electrically tunable exciton splitting. Using first-principles calculations, we propose that these are probably due to the emergence of a merely out-of-plane and momentum-independent spin splitting at and in the vicinity of the vertices of the WSe2 Brillouin zone under electric field. The non-magnetic approach for creating such an intriguing spin splitting keeps the system time-reversally invariant, thereby suggesting a new method for manipulating the spin degrees of freedom of electrons
Electrical injection and detection of spin-polarized currents in topological insulator Bi2Te2Se
Newtype large Rashba splitting in quantum well states induced by spin chirality in metal/topological insulator heterostructures
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Sn-doped Bi1.1Sb0.9Te2S bulk crystal topological insulator with excellent properties
A long-standing issue in topological insulator research has been to find a bulk single crystal material that provides a high-quality platform for characterizing topological surface states without interference from bulk electronic states. This material would ideally be a bulk insulator, have a surface state Dirac point energy well isolated from the bulk valence and conduction bands, display quantum oscillations from the surface state electrons and be growable as large, high-quality bulk single crystals. Here we show that this material obstacle is overcome by bulk crystals of lightly Sn-doped Bi(1.1)Sb(0.9)Te(2)S grown by the vertical Bridgman method. We characterize Sn-BSTS via angle-resolved photoemission spectroscopy, scanning tunnelling microscopy, transport studies, X-ray diffraction and Raman scattering. We present this material as a high-quality topological insulator that can be reliably grown as bulk single crystals and thus studied by many researchers interested in topological surface states