52 research outputs found
Reconstruction, rumpling, and Dirac states at the (001) surface of a topological crystalline insulator Pb1-xSnxSe
Equilibrium atomic configuration and electronic structure of the (001)
surface of IV-VI semiconductors PbTe, PbSe, SnTe and SnSe, is studied using the
density functional theory (DFT) methods. At surfaces of all those compounds,
the displacements of ions from their perfect lattice sites reveal two features
characteristic of the rock salt crystals. First, the ionic displacements occur
only along the direction perpendicular to the surface, and they exhibit the
rumpling effect, i.e., the vertical shifts of cations and anions differ.
Second, the interlayer spacing of the first few monolayers at the surface
oscillates. Our results are in good agreement with the previous X-ray
experimental data and theoretical results where available. They also are
consistent with the presence of two {110} mirror planes at the (001) surface of
the rock salt. One the other hand, experiments preformed for the topological
PbSn Se alloy indicate breaking of the mirror symmetry due to a
large 0.3 {\AA} relative displacement of the cation and anion sublattices at
the surface, which induces the opening of the gap of the Dirac cones. Our
results for PbSnSe including the simulated STM images, are in
contradiction with these findings, since surface reconstructions with broken
symmetry are never the ground state configurations. The impact of the
theoretically determined surface configurations and of the chemical disorder on
the surface states is analyzed.Comment: 9 pages, 11 figure
Plasmonic terahertz detectors based on a high-electron mobility GaAs/AlGaAs heterostructure
In order to characterize magnetic-field (B) tunable THz plasmonic detectors,
spectroscopy experiments were carried out at liquid helium temperatures and
high magnetic fields on devices fabricated on a high electron mobility
GaAs/AlGaAs heterostructure. The samples were either gated (the gate of a
meander shape) or ungated. Spectra of a photovoltage generated by THz radiation
were obtained as a function of B at a fixed THz excitation from a THz laser or
as a function of THz photon frequency at a fixed B with a Fourier spectrometer.
In the first type of measurements, the wave vector of magnetoplasmons excited
was defined by geometrical features of samples. It was also found that the
magnetoplasmon spectrum depended on the gate geometry which gives an additional
parameter to control plasma excitations in THz detectors. Fourier spectra
showed a strong dependence of the cyclotron resonance amplitude on the
conduction-band electron filling factor which was explained within a model of
the electron gas heating with the THz radiation. The study allows to define
both the advantages and limitations of plasmonic devices based on high-mobility
GaAs/AlGaAs heterostructures for THz detection at low temperatures and high
magnetic fields.Comment: 8 pages, 11 figure
Electrons in a ferromagnetic metal with a domain wall
We present theoretical description of conduction electrons interacting with a
domain wall in ferromagnetic metals. The description takes into account
interaction between electrons. Within the semiclassical approximation we
calculate the spin and charge distributions, particularly their modification by
the domain wall. In the same approximation we calculate local transport
characteristics, including relaxation times and charge and spin conductivities.
It is shown that these parameters are significantly modified near the wall and
this modification depends on electron-electron interaction.Comment: 10 pages with 4 figure
Conductance spectra of (Nb, Pb, In)/NbP -- superconductor/Weyl semimetal junctions
The possibility of inducing superconductivity in type-I Weyl semimetal
through coupling its surface to a superconductor was investigated. A single
crystal of NbP, grown by chemical vapor transport method, was carefully
characterized by XRD, EDX, SEM, ARPES techniques and by electron transport
measurements. The mobility spectrum of the carriers was determined. For the
studies of interface transmission, the (001) surface of the crystal was covered
by several hundred nm thick metallic layers of either Pb, or Nb, or In. DC
current-voltage characteristics and AC differential conductance through the
interfaces as a function of the DC bias were investigated. When the metals
become superconducting, all three types of junctions show conductance increase,
pointing out the Andreev reflection as a prevalent contribution to the subgap
conductance. In the case of Pb-NbP and Nb-NbP junctions, the effect is
satisfactorily described by modified Blonder-Tinkham-Klapwijk model. The
absolute value of the conductance is much smaller than that for the bulk
crystal, indicating that the transmission occurs through only a small part of
the contact area. An opposite situation occurs in In-NbP junction, where the
conductance at the peak reaches the bulk value indicating that almost whole
contact area is transmitting and, additionally, a superconducting proximity
phase is formed in the material. We interpret this as a result of indium
diffusion into NbP, where the metal atoms penetrate the surface barrier and
form very transparent superconductor-Weyl semimetal contact inside. However,
further diffusion occurring already at room temperature leads to degradation of
the effect, so it is observed only in the pristine structures. Despite of this,
our observation directly demonstrates possibility of inducing superconductivity
in a type-I Weyl semimetal.Comment: Accepted for Phys. Rev. B. 13 pages, 12 figures. Second version with
major revisions. The title was changed. One author R. Jakiela added. New
inset to Fig. 8(A). New fits in Fig. 8 (B) and Fig. 10 (B). Added figures 12
(C)-(E). Added Fig. 12 (F) with SIMS data. Rewritten chapters III-C-2 and
III-C-3. Reference no. 38 removed, 11 new references: 9, 21, 22, 40-44, 46-49
were adde
Effect of bulk inversion asymmetry on the Datta-Das transistor
A model of the Datta-Das spin field-effect transistor is presented which, in
addition to the Rashba interaction, takes into account the influence of bulk
inversion asymmetry of zinc-blende semiconductors. In the presence of bulk
inversion asymmetry, the conductance is found to depend significantly on the
crystallographic orientation of the channel. We determine the channel direction
optimal for the observation of the Datta-Das effect in GaAs and InAs-based
devices.Comment: 4 pages, Revtex4, 4 EPS figure
Investigation of the ferromagnetic transition in the correlated 4d perovskites SrRuRhO
The solid-solution SrRuRhO () is a
variable-electron-configuration system forming in the nearly-cubic-perovskite
basis, ranging from the ferromagnetic 4 to the enhanced paramagnetic
4. Polycrystalline single-phase samples were obtained over the whole
composition range by a high-pressure-heating technique, followed by
measurements of magnetic susceptibility, magnetization, specific heat,
thermopower, and electrical resistivity. The ferromagnetic order in long range
is gradually suppressed by the Rh substitution and vanishes at .
The electronic term of specific-heat shows unusual behavior near the critical
Rh concentration; the feature does not match even qualitatively with what was
reported for the related perovskites (Sr,Ca)RuO. Furthermore, another
anomaly in the specific heat was observed at .Comment: Accepted for publication in PR
Field Effect Transistors for Terahertz Detection: Physics and First Imaging Applications
Resonant frequencies of the two-dimensional plasma in FETs increase with the
reduction of the channel dimensions and can reach the THz range for sub-micron
gate lengths. Nonlinear properties of the electron plasma in the transistor
channel can be used for the detection and mixing of THz frequencies. At
cryogenic temperatures resonant and gate voltage tunable detection related to
plasma waves resonances, is observed. At room temperature, when plasma
oscillations are overdamped, the FET can operate as an efficient broadband THz
detector. We present the main theoretical and experimental results on THz
detection by FETs in the context of their possible application for THz imaging.Comment: 22 pages, 12 figures, review pape
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