In two waveguide heterostructures with quantum-well arrays of Hg
0.892
Cd
0.108
Te/Cd
0.63
Hg
0.37
Te with a thickness of 6.1 nm and Hg
0.895
Cd
0.105
Te/Cd
0.66
Hg
0.34
Te with a thickness of 7.4 ...nm, stimulated emission is first obtained at wavelengths of 10.3 and 14 μm under continuous optical excitation at 8 K. It is shown that, due to the presence of Cd in the quantum wells, the effect of fluctuations in the thickness of the quantum wells on the energy of interband transitions in it decreases, which can ultimately cause a significant decrease in the threshold intensity for stimulated emission.
Herein, studies of the cyclotron resonance (CR) in thick CdxHg1−xTe films with different cadmium contents corresponding to materials with and without band inversion, as well as critical content ...corresponding to an almost linear energy dispersion are presented. The results demonstrate that the formation of 2D topological surface states requires sharp interfaces between layers with and without band inversion, in which case the corresponding CR is clearly observed for the out‐of‐plane orientation of magnetic field but does not show up for an in‐plane orientation. In contrast, all samples having more conventional technological design with smooth interfaces (i.e., containing regions of CdxHg1−xTe with gradually changing Cd content x) show equally pronounced CR in both in‐plane and out‐of‐plane magnetic field revealing that CR is excited in effectively 3D states. Modeling of the surface states for different film designs supports main observations. In all samples, additional broad helicity‐independent resonances are observed, which are attributed to photoionization and magnetic freeze‐out of impurity states.
Herein, studies of the cyclotron resonance in CdxHg1−xTe films demonstrate that the formation of 2D topological surface states requires sharp interfaces between layers with and without band inversion. Exclusively for sharp interfaces, the corresponding CR is clearly observed for the out‐of‐plane orientation of magnetic field but does not show up for an in‐plane orientation.
It has been shown that locally measuring coercive force
based on the magnitude of demagnetizing current has a fundamental limitation on the measurement range. We have demonstrated the expediency of ...measuring coercive force in ferromagnetic objects locally, based on the magnitude of the tangential component of the magnetic field in the interpole space on the surface of the test object, that is, based on the internal field. This allows one to expand the range of measured values
by several times. Also, the influence of the gap between the transducer and the object, as well as the shape and size of test objects on the measurement results is significantly reduced. This makes it possible to measure the absolute values of
of homogeneous ferromagnetic objects, as well as the coercive force of objects with nonferromagnetic coatings of considerable thickness.
Wires made of topological insulators (TI) are a promising platform for searching for Majorana bound states. These states can be probed by analyzing the fractional ac Josephson effect in Josephson ...junctions with the TI wire as a weak link. An axial magnetic field can be used to tune the system from trivial to topologically nontrivial. Here, we investigate the oscillations of the supercurrent in such wire Josephson junctions as a function of the axial magnetic field strength and different contact transparencies. Although the current flows on average parallel to the magnetic field we observe h/2e, h/4e, and even h/8e periodic oscillations of the supercurrent in samples with lower contact transparencies. Corresponding tight-binding transport simulations using a Bogoliubov-de Gennes model Hamiltonian yield the supercurrent through the Josephson junctions, showing in particular the peculiar h/4e-periodic oscillations observed in experiments. A further semiclassical analysis based on Andreev-reflected trajectories connecting the two superconductors allows us to identify the physical origin of these oscillations. They can be related to flux-enclosing paths winding around the TI nanowire, thereby highlighting the threedimensional character of the junction geometry compared to common planar junctions.
We study the transport properties of HgTe quantum wells with critical well thickness, where the band gap is closed and the low energy spectrum is described by a single Dirac cone. In this work, we ...examined both macroscopic and micron-sized (mesoscopic) samples. In micron-sized samples, we observe a magnetic-field-induced quantized resistance (~h/2e) at Landau filling factor ν=0, corresponding to the formation of helical edge states centered at the charge neutrality point (CNP). In macroscopic samples, the resistance near a zero Landau level (LL) reveals strong oscillations, which we attribute to scattering between the edge ν=0 state and bulk ν≠0 hole LL. We provide a model taking an empirical approach to construct a LL diagram based on a reservoir scenario, formed by the heavy holes.
Mercury cadmium telluride
n
-Hg
1 –
x
Cd
x
Te (HgCdTe) films with near-surface wide-bangap layers were grown by molecular beam epitaxy on Si(013) substrates. Admittance of the ...metal–insulator–semiconductor (MIS) structure was measured in samples based on the initial HgCdTe film and the same films after implantation with As
+
ions and after subsequent thermal annealing. Methods taking into account the presence of near-surface graded-gap layers and slow surface states were used to determine the main parameters of these layers upon technological procedures involved in the production of photodiodes.
We investigate the superradiance effects in three-dimensional topological insulator HgTe with conducting surface states. We demonstrate that the superradiance can be explained using the classical ...electrodynamic approach. Experiments using the continuous-wave spectroscopy allowed us to separate the energy losses in the system into intrinsic and radiation losses, respectively. These results demonstrate that the superradiance effects are not sensitive to the details of the band structure of the material.
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