119 research outputs found
Current-induced magnetization switching in a magnetic topological insulator heterostructure
We present the current-induced switching of the internal magnetization
direction in a magnetic topological insulator/topological insulator
heterostructure in the quantum anomalous Hall regime. The switching process is
based on the bias current dependence of the coercive field, which is attributed
to the effect of the spin-orbit torque provided by the unpolarized bias
current. Increasing the bias current leads to a decrease in the magnetic order
in the sample. When the applied current is subsequently reduced, the magnetic
moments align with an externally applied magnetic field, resulting in
repolarization in the opposite direction. This includes a reversal of the spin
polarisation and hence a reversal of the chiral edge mode. Possible
applications in spintronic devices are discussed.Comment: 6 pages, 3 figures (5 pages and 5 figures in supplementary
information
Influence of the First Preparation Steps on the Properties of GaN Layers Grown on 6H-SIC by Mbe
AbstractThe Gan heteroepitaxy on 6H-SiC is affected by the bad morphology of the substrate surface. We performed a hydrogen etching at 1550°C on the 6H-SiC(0001) substrates to obtain atomically flat terraces. An improvement of the structural properties of GaN grown by MBE on such substrates after deposition of a LT-AIN buffer layer is observed. A value of less than 220 arcsec of the FWHM of the XRD rocking curve, showing a reduced screw dislocations density, is comparable with the best results reported until now for thick GaN samples. Photoluminescence showed a structured near band edge emission spectrum with evidence of the A, B and C free exciton recombinations
Роль когнитивно-ономасиологического метода в изучении терминов
Ономасиологический подход к исследованию производных единиц номинации предполагает выделение трёх основных категорий: ономасиологического базиса, ономасиологического признака и предиката, который связывает базис и признак определенным отношением. Ономасиологический базис, выраженный основой термина, играет ведущую роль в первичной категоризации специального понятия, в определении его места в научной картине мира.
Дальнейшая субкатегоризация связана с ономасиологическим признаком, отражающим различные предметные и непредметные сущности.
Метод направлен на объяснение связи ономасиологической структуры со структурами знаний об объекте номинации, а значит с концептами и категориями
Quantum transport in topological surface states of BiTe nanoribbons
Quasi-1D nanowires of topological insulators are emerging candidate
structures in superconductor hybrid architectures for the realization of
Majorana fermion based quantum computation schemes. It is however technically
difficult to both fabricate as well as identify the 1D limit of topological
insulator nanowires. Here, we investigated selectively-grown BiTe
topological insulator nanoribbons and nano Hall bars at cryogenic temperatures
for their topological properties. The Hall bars are defined in deep-etched
SiN/SiO nano-trenches on a silicon (111) substrate followed by a
selective area growth process via molecular beam epitaxy. The selective area
growth is beneficial to the device quality, as no subsequent fabrication needs
to be performed to shape the nanoribbons. Transmission line measurements are
performed to evaluate contact resistances of Ti/Au contacts applied as well as
the specific resistance of the BiTe binary topological insulator. In
the diffusive transport regime of these unintentionally -doped BiTe
topological insulator nano Hall bars, we identify distinguishable electron
trajectories by analyzing angle-dependent universal conductance fluctuation
spectra. When the sample is tilted from a perpendicular to a parallel magnetic
field orientation, these high frequent universal conductance fluctuations merge
with low frequent Aharonov-Bohm type oscillations originating from the
topologically protected surface states encircling the nanoribbon cross section.
For 500 nm wide Hall bars we also identify low frequent Shubnikov-de Haas
oscillations in the perpendicular field orientation, that reveal a topological
high-mobility 2D transport channel, partially decoupled from the bulk of the
material.Comment: 13 pages, 5 figures, 6 pages supplementary information, 5
supplementary figure
Gate-induced decoupling of surface and bulk state properties in selectively-deposited BiTe nanoribbons
Three-dimensional topological insulators (TIs) host helical Dirac surface
states at the interface with a trivial insulator. In quasi-one-dimensional TI
nanoribbon structures the wave function of surface charges extends
phase-coherently along the perimeter of the nanoribbon, resulting in a
quantization of transverse surface modes. Furthermore, as the inherent
spin-momentum locking results in a Berry phase offset of of
self-interfering charge carriers an energy gap within the surface state
dispersion appears and all states become spin-degenerate. We investigate and
compare the magnetic field dependent surface state dispersion in selectively
deposited BiTe TI micro- and nanoribbon structures by analysing the
gate voltage dependent magnetoconductance at cryogenic temperatures. While in
wide microribbon devices the field effect mainly changes the amount of bulk
charges close to the top surface we identify coherent transverse surface states
along the perimeter of the nanoribbon devices responding to a change in top
gate potential. We quantify the energetic spacing in between these quantized
transverse subbands by using an electrostatic model that treats an initial
difference in charge carrier densities on the top and bottom surface as well as
remaining bulk charges. In the gate voltage dependent transconductance we find
oscillations that change their relative phase by at half-integer values
of the magnetic flux quantum applied coaxial to the nanoribbon, which is a
signature for a magnetic flux dependent topological phase transition in narrow,
selectively deposited TI nanoribbon devices.Comment: 11 pages, 5 figure
In-plane magnetic field-driven symmetry breaking in topological insulator-based three-terminal junctions
Topological surface states of three-dimensional topological insulator
nanoribbons and their distinct magnetoconductance properties are promising for
topoelectronic applications and topological quantum computation. A crucial
building block for nanoribbon-based circuits are three-terminal junctions.
While the transport of topological surface states on a planar boundary is not
directly affected by an in-plane magnetic field, the orbital effect cannot be
neglected when the surface states are confined to the boundary of a nanoribbon
geometry. Here, we report on the magnetotransport properties of such
three-terminal junctions. We observe a dependence of the current on the
in-plane magnetic field, with a distinct steering pattern of the surface state
current towards a preferred output terminal for different magnetic field
orientations. We demonstrate that this steering effect originates from the
orbital effect, trapping the phase-coherent surface states in the different
legs of the junction on opposite sides of the nanoribbon and breaking the
left-right symmetry of the transmission across the junction. The reported
magnetotransport properties demonstrate that an in-plane magnetic field is not
only relevant but also very useful for the characterization and manipulation of
transport in three-dimensional topological insulator nanoribbon-based junctions
and circuits, acting as a topoelectric current switch.Comment: Main Text (8 pages, 5 figures) + Supplemental Material (13 pages, 10
figures
C11 of IUPAP: Report by the Working Group on Authorship in Large Scientific Collaborations in Experimental High Energy Physics
Solid surfaces, interfaces and thin films
This book emphasises both experimental and theoretical aspects of surface, interface and thin-film physics. As in previous editions the preparation of surfaces and thin films, their atomic and morphological structure, their vibronic and electronic properties as well as fundamentals of adsorption are treated. Because of their importance in modern information technology and nanostructure research, particular emphasis is paid to electronic surface and interface states, semiconductor space charge layers and heterostructures. A special chapter of the book is devoted to collective phenomena at interfaces and in thin films such as superconductivity and magnetism. The latter topic includes the meanwhile important issues giant magnetoresistance and spin-transfer torque mechanism, both effects being of high interest in information technology. In this new edition, for the first time, the effect of spin-orbit coupling on surface states is treated. In this context the class of the recently detected topological insulators, materials of significant importance for spin electronics, are discussed. Particular emphasis, hereby, is laid on the new type of topologically protected surface states with well-defined spin orientation. Furthermore, some important well established experimental techniques such as X-ray diffraction (XRD) and reflection anisotropy spectroscopy (RAS), which were missing so far in earlier editions, were added in this new 6th edition of the book
Quantum physics in the nanoworld: Schrödinger's cat and the dwarfs
The book deals with all essential aspects of non-relativistic quantum physics up to the quantization of fields. In contrast to common textbooks of quantum mechanics, modern experiments are described both for the purpose of foundation of the theory and in relation to recent applications. In this respect applications to nano-electronics as well as the realization of quantum-bits are presented and discussed. Furthermore, links are made to other important research fields and applications, such as elementary particle physics, solid state physics and nuclear magnetic resonance tomography in medicine. Even though the representation of the topics is largely performed in terms of Dirac´s bra-ket notation and by use of commutator algebra, the concrete description of the physical basis and the corresponding theoretical concepts are emphasized. Because of little requirement of complex mathematics, the book is suitable as an introduction into quantum physics, not only for physicists but also for chemists, biologists, engineers, computer scientists and even for philosophers as far as they are interested in natural philosophy and epistomology
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