271 research outputs found
Observation of correlated spin-orbit order in a strongly anisotropic quantum wire system
Quantum wires with spin-orbit coupling provide a unique opportunity to
simultaneously control the coupling strength and the screened Coulomb
interactions where new exotic phases of matter can be explored. Here we report
on the observation of an exotic spin-orbit density wave in Pb-atomic wires on
Si(557) surfaces by mapping out the evolution of the modulated spin-texture at
various conditions with spin- and angle-resolved photoelectron spectroscopy.
The results are independently quantified by surface transport measurements. The
spin polarization, coherence length, spin dephasing rate, and the associated
quasiparticle gap decrease simultaneously as the screened Coulomb interaction
decreases with increasing excess coverage, providing a new mechanism for
generating and manipulating a spin-orbit entanglement effect via electronic
interaction. Despite clear evidence of spontaneous spin-rotation symmetry
breaking and modulation of spin-momentum structure as a function of excess
coverage, the average spin-polarization over the Brillouin zone vanishes,
indicating that time-reversal symmetry is intact as theoretically predicted
Tuning independently Fermi energy and spin splitting in Rashba systems: Ternary surface alloys on Ag(111)
By detailed first-principles calculations we show that the Fermi energy and
the Rashba splitting in disordered ternary surface alloys (BiPbSb)/Ag(111) can
be independently tuned by choosing the concentrations of Bi and Pb. The
findings are explained by three fundamental mechanisms, namely the relaxation
of the adatoms, the strength of the atomic spin-orbit coupling, and band
filling. By mapping the Rashba characteristics,i.e.the splitting and the Rashba
energy, and the Fermi energy of the surface states in the complete range of
concentrations. Our results suggest to investigate experimentally effects which
rely on the Rashba spin-orbit coupling in dependence on spin-orbit splitting
and band filling.Comment: 11 pages, 3 figure
First observation of spin-helical Dirac fermions and topological phases in undoped and doped Bi2Te3 demonstrated by spin-ARPES spectroscopy
Electron systems that possess light-like dispersion relations or the conical
Dirac spectrum, such as graphene and bismuth, have recently been shown to
harbor unusual collective states in high magnetic fields. Such states are
possible because their light-like electrons come in spin pairs that are
chiral,which means that their direction of propagation is tied to a quantity
called pseudospin that describes their location in the crystal lattice. An
emerging direction in quantum materials research is the manipulation of atomic
spin-orbit coupling to simulate the effect of a spin dependent magnetic
field,in attempt to realize novel spin phases of matter. This effect has been
proposed to realize systems consisting of unpaired Dirac cones that are
helical, meaning their direction of propagation is tied to the electron spin
itself, which are forbidden to exist in graphene or bismuth. The experimental
existence of topological order can not be determined without spin-resolved
measurements. Here we report a spin-and angle-resolved photoemission study of
the hexagonal surface of the Bi2Te3 and Bi{2-x}MnxTe3 series, which is found to
exhibit a single helical Dirac cone that is fully spin-polarized. Our
observations of a gap in the bulk spin-degenerate band and a spin-resolved
surface Dirac node close to the chemical potential show that the low energy
dynamics of Bi2Te3 is dominated by the unpaired spin-helical Dirac modes. Our
spin-texture measurements prove the existence of a rare topological phase in
this materials class for the first time, and suggest its suitability for novel
2D Dirac spin device applications beyond the chiral variety or traditional
graphene.Comment: 13 pages, 4 figure
Orbit- and Atom-Resolved Spin Textures of Intrinsic, Extrinsic and Hybridized Dirac Cone States
Combining first-principles calculations and spin- and angle-resolved
photoemission spectroscopy measurements, we identify the helical spin textures
for three different Dirac cone states in the interfaced systems of a 2D
topological insulator (TI) of Bi(111) bilayer and a 3D TI Bi2Se3 or Bi2Te3. The
spin texture is found to be the same for the intrinsic Dirac cone of Bi2Se3 or
Bi2Te3 surface state, the extrinsic Dirac cone of Bi bilayer state induced by
Rashba effect, and the hybridized Dirac cone between the former two states.
Further orbit- and atom-resolved analysis shows that s and pz orbits have a
clockwise (counterclockwise) spin rotation tangent to the iso-energy contour of
upper (lower) Dirac cone, while px and py orbits have an additional radial spin
component. The Dirac cone states may reside on different atomic layers, but
have the same spin texture. Our results suggest that the unique spin texture of
Dirac cone states is a signature property of spin-orbit coupling, independent
of topology
Universal response of the type-II Weyl semimetals phase diagram
The discovery of Weyl semimetals represents a significant advance in
topological band theory. They paradigmatically enlarged the classification of
topological materials to gapless systems while simultaneously providing
experimental evidence for the long-sought Weyl fermions. Beyond fundamental
relevance, their high mobility, strong magnetoresistance, and the possible
existence of even more exotic effects, such as the chiral anomaly, make Weyl
semimetals a promising platform to develop radically new technology. Fully
exploiting their potential requires going beyond the mere identification of
materials and calls for a detailed characterization of their functional
response, which is severely complicated by the coexistence of surface- and
bulk-derived topologically protected quasiparticles, i.e., Fermi arcs and Weyl
points, respectively. Here, we focus on the type-II Weyl semimetal class where
we find a stoichiometry-dependent phase transition from a trivial to a
non-trivial regime. By exploring the two extreme cases of the phase diagram, we
demonstrate the existence of a universal response of both surface and bulk
states to perturbations. We show that quasi-particle interference patterns
originate from scattering events among surface arcs. Analysis reveals that
topologically non-trivial contributions are strongly suppressed by spin
texture. We also show that scattering at localized impurities generate
defect-induced quasiparticles sitting close to the Weyl point energy. These
give rise to strong peaks in the local density of states, which lift the Weyl
node significantly altering the pristine low-energy Weyl spectrum. Visualizing
the microscopic response to scattering has important consequences for
understanding the unusual transport properties of this class of materials.
Overall, our observations provide a unifying picture of the Weyl phase diagram
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