125 research outputs found
Structural phase transition in IrTe: A combined study of optical spectroscopy and band structure calculations
IrPtTe is an interesting system showing competing phenomenon
between structural instability and superconductivity. Due to the large atomic
numbers of Ir and Te, the spin-orbital coupling is expected to be strong in the
system which may lead to nonconventional superconductivity. We grew single
crystal samples of this system and investigated their electronic properties. In
particular, we performed optical spectroscopic measurements, in combination
with density function calculations, on the undoped compound IrTe in an
effort to elucidate the origin of the structural phase transition at 280 K. The
measurement revealed a dramatic reconstruction of band structure and a
significant reduction of conducting carriers below the phase transition. We
elaborate that the transition is not driven by the density wave type
instability but caused by the crystal field effect which further
splits/separates the energy levels of Te (p, p) and Te p bands.Comment: 16 pages, 5 figure
A topological insulator surface under strong Coulomb, magnetic and disorder perturbations
Three dimensional topological insulators embody a newly discovered state of
matter characterized by conducting spin-momentum locked surface states that
span the bulk band gap as demonstrated via spin-resolved ARPES measurements .
This highly unusual surface environment provides a rich ground for the
discovery of novel physical phenomena. Here we present the first controlled
study of the topological insulator surfaces under strong Coulomb, magnetic and
disorder perturbations. We have used interaction of iron, with a large Coulomb
state and significant magnetic moment as a probe to \textit{systematically test
the robustness} of the topological surface states of the model topological
insulator BiSe. We observe that strong perturbation leads to the
creation of odd multiples of Dirac fermions and that magnetic interactions
break time reversal symmetry in the presence of band hybridization. We also
present a theoretical model to account for the altered surface of BiSe.
Taken collectively, these results are a critical guide in manipulating
topological surfaces for probing fundamental physics or developing device
applications.Comment: 14 pages, 4 Figures. arXiv admin note: substantial text overlap with
arXiv:1009.621
Band structure engineering in (Bi1-xSbx)2Te3 ternary topological insulators
Three-dimensional (3D) topological insulators (TI) are novel quantum
materials with insulating bulk and topologically protected metallic surfaces
with Dirac-like band structure. The spin-helical Dirac surface states are
expected to host exotic topological quantum effects and find applications in
spintronics and quantum computation. The experimental realization of these
ideas requires fabrication of versatile devices based on bulk-insulating TIs
with tunable surface states. The main challenge facing the current TI materials
exemplified by Bi2Se3 and Bi2Te3 is the significant bulk conduction, which
remains unsolved despite extensive efforts involving nanostructuring, chemical
doping and electrical gating. Here we report a novel approach for engineering
the band structure of TIs by molecular beam epitaxy (MBE) growth of
(Bi1-xSbx)2Te3 ternary compounds. Angle-resolved photoemission spectroscopy
(ARPES) and transport measurements show that the topological surface states
exist over the entire composition range of (Bi1-xSbx)2Te3 (x = 0 to 1),
indicating the robustness of bulk Z2 topology. Most remarkably, the systematic
band engineering leads to ideal TIs with truly insulating bulk and tunable
surface state across the Dirac point that behave like one quarter of graphene.
This work demonstrates a new route to achieving intrinsic quantum transport of
the topological surface states and designing conceptually new TI devices with
well-established semiconductor technology.Comment: Minor changes in title, text and figures. Supplementary information
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Ripple modulated electronic structure of a 3D topological insulator
3D topological insulators, similar to the Dirac material graphene, host
linearly dispersing states with unique properties and a strong potential for
applications. A key, missing element in realizing some of the more exotic
states in topological insulators is the ability to manipulate local electronic
properties. Analogy with graphene suggests a possible avenue via a topographic
route by the formation of superlattice structures such as a moir\'e patterns or
ripples, which can induce controlled potential variations. However, while the
charge and lattice degrees of freedom are intimately coupled in graphene, it is
not clear a priori how a physical buckling or ripples might influence the
electronic structure of topological insulators. Here we use Fourier transform
scanning tunneling spectroscopy to determine the effects of a one-dimensional
periodic buckling on the electronic properties of Bi2Te3. By tracking the
spatial variations of the scattering vector of the interference patterns as
well as features associated with bulk density of states, we show that the
buckling creates a periodic potential modulation, which in turn modulates the
surface and the bulk states. The strong correlation between the topographic
ripples and electronic structure indicates that while doping alone is
insufficient to create predetermined potential landscapes, creating ripples
provides a path to controlling the potential seen by the Dirac electrons on a
local scale. Such rippled features may be engineered by strain in thin films
and may find use in future applications of topological insulators.Comment: Nature Communications (accepted
Tunable Multifunctional Topological Insulators in Ternary Heusler Compounds
Recently the Quantum Spin Hall effect (QSH) was theoretically predicted and
experimentally realized in a quantum wells based on binary semiconductor
HgTe[1-3]. QSH state and topological insulators are the new states of quantum
matter interesting both for fundamental condensed matter physics and material
science[1-11]. Many of Heusler compounds with C1b structure are ternary
semiconductors which are structurally and electronically related to the binary
semiconductors. The diversity of Heusler materials opens wide possibilities for
tuning the band gap and setting the desired band inversion by choosing
compounds with appropriate hybridization strength (by lattice parameter) and
the magnitude of spin-orbit coupling (by the atomic charge). Based on the
first-principle calculations we demonstrate that around fifty Heusler compounds
show the band inversion similar to HgTe. The topological state in these
zero-gap semiconductors can be created by applying strain or by designing an
appropriate quantum well structure, similar to the case of HgTe. Many of these
ternary zero-gap semiconductors (LnAuPb, LnPdBi, LnPtSb and LnPtBi) contain the
rare earth element Ln which can realize additional properties ranging from
superconductivity (e. g. LaPtBi[12]) to magnetism (e. g. GdPtBi[13]) and
heavy-fermion behavior (e. g. YbPtBi[14]). These properties can open new
research directions in realizing the quantized anomalous Hall effect and
topological superconductors.Comment: 20 pages, 5 figure
Spin-Rotation Symmetry Breaking in the Superconducting State of CuxBi2Se3
Spontaneous symmetry breaking is an important concept for understanding
physics ranging from the elementary particles to states of matter. For example,
the superconducting state breaks global gauge symmetry, and unconventional
superconductors can break additional symmetries. In particular, spin rotational
symmetry is expected to be broken in spin-triplet superconductors. However,
experimental evidence for such symmetry breaking has not been conclusively
obtained so far in any candidate compounds. Here, by 77Se nuclear magnetic
resonance measurements, we show that spin rotation symmetry is spontaneously
broken in the hexagonal plane of the electron-doped topological insulator
Cu0.3Bi2Se3 below the superconducting transition temperature Tc=3.4 K. Our
results not only establish spin-triplet superconductivity in this compound, but
may also serve to lay a foundation for the research of topological
superconductivity
A road to reality with topological superconductors
Topological states of matter are a source of low-energy quasiparticles, bound
to a defect or propagating along the surface. In a superconductor these are
Majorana fermions, described by a real rather than a complex wave function. The
absence of complex phase factors promises protection against decoherence in
quantum computations based on topological superconductivity. This is a tutorial
style introduction written for a Nature Physics focus issue on topological
matter.Comment: pre-copy-editing, author-produced version of the published paper: 4
pages, 2 figure
Hedgehog Spin-texture and Berry's Phase tuning in a Magnetic Topological Insulator
Understanding and control of spin degrees of freedom on the surfaces of
topological materials are key to future applications as well as for realizing
novel physics such as the axion electrodynamics associated with time-reversal
(TR) symmetry breaking on the surface. We experimentally demonstrate
magnetically induced spin reorientation phenomena simultaneous with a
Dirac-metal to gapped-insulator transition on the surfaces of manganese-doped
Bi2Se3 thin films. The resulting electronic groundstate exhibits unique
hedgehog-like spin textures at low energies, which directly demonstrate the
mechanics of TR symmetry breaking on the surface. We further show that an
insulating gap induced by quantum tunnelling between surfaces exhibits spin
texture modulation at low energies but respects TR invariance. These spin
phenomena and the control of their Fermi surface geometrical phase first
demonstrated in our experiments pave the way for the future realization of many
predicted exotic magnetic phenomena of topological origin.Comment: 38 pages, 18 Figures, Includes new text, additional datasets and
interpretation beyond arXiv:1206.2090, for the final published version see
Nature Physics (2012
Independent measure of the neutrino mixing angle θ13 via neutron capture on hydrogen at Daya Bay
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