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Near-surface layers of the mercury chalcogenide (HgSe and n-HgTe) single crystals with the electron concentration in the range of 7 × 1014–4.2 × 1018 сm−3 were studied using the laser pump-probe thermoreflectance (TR) technique combined with the Fabry–Perot (FP) interferometer in the wide temperature interval of 10–300= K. The TR–FP measurements were carried out toward samples with a freshly etched reflective surface. As a result, a minimum in the time dependence of the TR–FP signal and sign inversion of the TR–FP signal were revealed both for HgSe and n-HgTe within the specified temperature range. Noticeably, both anomalies were observed for n-HgTe at substantially lower temperatures than that for HgSe. The proposed qualitative interpretation of the observed anomalies is based on the hypothesis of two types of Weyl nodes located in the Brillouin zone of mercury chalcogenides involving specific for the Weyl semimetals energy barriers, separating the bulk Weyl fermion helical states from the topologically protected Fermi-arc surface states. [ABSTRACT FROM AUTHOR]

WT e 2 is a material with rich topological properties: it is a 2D topological insulator as a monolayer and a Weyl-semimetal and higher-order topological insulator in a bulk form. Inducing superconductivity in topological materials is a way to obtain topological superconductivity, which lays at the foundation for many proposals of fault tolerant quantum computing. Here, we demonstrate the emergence of superconductivity at the interface between WT e 2 and the normal metal palladium. The superconductivity has a critical temperature of about 1.2 K. By studying the superconductivity in a perpendicular magnetic field, we obtain the coherence length and the London penetration depth. These parameters correspond to a low Fermi velocity and a high density of states at the Fermi level. This hints to a possible origin of superconductivity due to the formation of flatbands. Furthermore, the critical in-plane magnetic field exceeds the Pauli limit, suggesting a non-trivial nature of the superconducting state. [ABSTRACT FROM AUTHOR]

We find an unusual anisotropy of the inplane field magnetoresistance with higher resistance in the parallel orientation of the field, Bǁ, and current, I, in ultra-high mobility SiGe/Si/SiGe quantum wells. The anisotropy depends on the orientation between the inplane field and the current relative to the crystallographic axes of the sample, and is a consequence of the ridges on the quantum well surface. For the parallel or perpendicular orientations between current and ridges, a method of converting the magnetoresistance measured at I⊥Bǁ into the one measured at I ǁ Bǁ is suggested and is shown to yield results that agree with the experiment. [ABSTRACT FROM AUTHOR]

We report on a detailed experimental study of the electron transport anisotropy in HgTe (013) quantum well of 22 nm width in the directions [ 100 ] and [ 03 1 ¯ ] as the electron density function n. The anisotropy is absent at the minimal electron density near a charge neutrality point. The anisotropy increases with the increase in n and reaches about 10% when the Fermi level is within the first subband H1. There is a sharp increase in the anisotropy (up to 60%) when the Fermi level reaches the second subband E2. We conclude that the first effect is due to the small intra-subband anisotropic interface roughness scattering, and the second one is due to the strongly anisotropic inter-subband roughness scattering, but the microscopical reason for such a strong change in the anisotropy remains unknown. [ABSTRACT FROM AUTHOR]

Intrinsic Si(111) surfaces passivated with atomic hydrogen are an ideal platform to host two-dimensional electron systems. Traditional methods to probe these surfaces, however, typically involve the placement of dopants and metals directly onto the surface and subsequent high temperature processing, which can be harsh and invasive and lead to surface degradation. Here, we detail a non-invasive gating approach for probing two-dimensional electron systems on intrinsic H-Si(111) surfaces using a silicon-on-insulator (SOI) gating assembly. In this architecture, all harsh device fabrication is performed on a single SOI chip, ensuring that the H-Si(111) surface remains in pristine condition, or as close to the original manufactured intrinsic-Si wafer as possible. To achieve this, we intentionally keep our H-Si(111) surfaces free of any dopants or metals, which are instead placed on the adjacent SOI chip. All electrical components, including Ohmic contacts and accumulation and depletion gates, are housed in the SOI piece. The Ohmic contacts on the SOI piece are brought into physical and electrical contact with the pristine H-Si(111) piece after being van der Waals bonded at room temperature, while all gates on the SOI piece are separated from the H-Si(111) surface by vacuum. Architecture details, baseline operation tests, and 77 K device characterization measurements will be discussed, as well as the implications of going beyond H-Si(111) surfaces and using our device architecture to facilitate transport measurements on halogen-terminated Si surfaces. [ABSTRACT FROM AUTHOR]

Charge transport in silicon is investigated on a metal-oxide-semiconductor structure, which is driven into depletion, accumulation, or inversion. Terahertz electromodulation spectroscopy provides momentum relaxation times as well as conductivity effective masses of electrons and holes. At room temperature the conductivity effective masses of electrons and holes are close to those values reported for cryogenic temperatures. [ABSTRACT FROM AUTHOR]

The combination of photoluminescence and magneto-transport measurements is used to study the single-particle relaxation time and the transport scattering time in short-period InGaAs/InP superlattices. Both the single-particle relaxation times of the electrons and of the holes were obtained in the same samples and were shown to be determined by the remote-impurity scattering. The transport scattering time for electrons was found to be dominated by the interface-roughness scattering with lateral length Λ=10 nm and height Δ = 0.13 nm. We also discuss the importance of multiple-scattering effects for small well widths and of alloy scattering for large well widths. [ABSTRACT FROM AUTHOR]

Recent experimental results regarding the transport properties of ZnO/MgZnO heterostructures with very high mobility (μ≤1.8×105cm2/Vs) are analyzed. In the electron density range of the experiment, the two-dimensional electron gas in ZnO/MgZnO heterostructures is strongly correlated with a large Wigner-Seitz parameter 4 < rs < 12. We demonstrate that many-body effects (exchange and correlation), described by a local-field correction, are very large in this density range. They reduce the screening properties of the two-dimensional electron gas and strongly reduce the transport scattering time and the single-particle relaxation time at low electron densities. For such samples, we also discuss the peak mobility, the metal-insulator transition, and the magnetoresistance in a parallel magnetic field. [ABSTRACT FROM AUTHOR]

We consider the mobility of the interacting two-dimensional electron gas as realized in SiGe/Si/SiGe quantum wells. For zero temperature we calculate the mobility as function of the electron density for remote charged-impurity scattering and we take into account exchange-correlation effects and multiple-scattering effects. Multiple-scattering effects give rise to a metal-insulator transition at low electron density. Our calculation is in good agreement with experimental results obtained with remote doped SiGe/Si/SiGe quantum wells having electron densities near the metal-insulator transition. We discuss the critical density of the metal-insulator transition as function of the remote doping distance and make some predictions. The single-particle relaxation time and spin-polarization effects are also considered. [ABSTRACT FROM AUTHOR]

We discuss the non-equilibrium properties of integer channels in nonuniform 2D electron (hole) systems in the presence of a strong magnetic field. The results are applied to a qualitative explanation of the Corbino disk current-voltage characteristics (IVC) in the quantum Hall effect (QHE) regime. Special consideration is paid to the so-called “QHE breakdown” effect, which is readily observed in both the Hall bar and Corbino geometries of the tested cells. The QHE breakdown is especially evident in the Corbino samples, allowing for a more in-depth study of these effects. [ABSTRACT FROM AUTHOR]

We report the observation of an electron gas in a SiGe/Si/SiGe quantum well with maximum mobility up to 240 m²/Vs, which is noticeably higher than previously reported results in siliconbased structures. Using SiO, rather than Al2O3, as an insulator, we obtain strongly reduced threshold voltages close to zero. In addition to the predominantly small-angle scattering well known in the high-mobility heterostructures, the observed linear temperature dependence of the conductivity reveals the presence of a short-range random potential. [ABSTRACT FROM AUTHOR]

We report the observation of an electron gas in a SiGe/Si/SiGe quantum well with maximum mobility up to 240 m2/Vs, which is noticeably higher than previously reported results in silicon-based structures. Using SiO, rather than Al2O3, as an insulator, we obtain strongly reduced threshold voltages close to zero. In addition to the predominantly small-angle scattering well known in the high-mobility heterostructures, the observed linear temperature dependence of the conductivity reveals the presence of a short-range random potential. [ABSTRACT FROM AUTHOR]

Here, we report on a transparent method to characterize individual layers in a double-layer electron system, which forms in a wide quantum well, and to determine their electron densities. The technique relies on the simultaneous measurement of the capacitances between the electron system and gates located on either side of the well. Modifications to the electron wave function due to the population of the second subband and the appearance of an additional electron layer can be detected. The magnetic field dependence of these capacitances is dominated by quantum corrections caused by the occupation of Landau levels in the nearest electron layer. The technique should be equally applicable to other implementations of a double layer electron system. [ABSTRACT FROM AUTHOR]

We demonstrate single photon counting of terahertz (THz) waves transmitted from a local THz point source through a coplanar two-wire waveguide on a GaAs/AlGaAs single heterostructure crystal. In the electrically driven all-in-one chip, quantum Hall edge transport is used to achieve a noiseless injection current for a monochromatic point source of THz fields. The local THz fields are coupled to a coplanar two-wire metal waveguide and transmitted over a macroscopic scale greater than the wavelength (38 μm in GaAs). THz waves propagating on the waveguide are counted as individual photons by a quantum-dot single-electron transistor on the same chip. Photon counting on integrated high-frequency circuits will open the possibilities for on-chip quantum optical experiments. [ABSTRACT FROM AUTHOR]

The paper describes and conceptualizes results of an experimental study of a new class of interferometers, electronic analogues of known optical interference schemes, in the quantum Hall effect regime, which are based on co-propagating edge states. [ABSTRACT FROM AUTHOR]

For interface-roughness scattering and for zero temperatures, we compare theoretical results for the transport properties of the electron gas present in thin AlAs quantum wells with experimental results for a well of width L=45 Å. The importance of a density dependent effective mass is discussed. For the mobility, reasonable agreement between theory and experiment is obtained by taking into account multiple scattering effects, which lead to a metal-insulator transition. We predict the single-particle relaxation time. With a density dependent effective mass, the calculated critical electron density of the metal-insulator transition is found to be in good agreement with the experimental value. [ABSTRACT FROM AUTHOR]

We demonstrate a self-switching effect of narrow current channels, which allows the control of multiterminal junctions without using external gates. The self-switching leads to negative differential resistance and is interpreted in terms of a bias voltage controlled gating of the junction and the injection of electrons from different terminals. The self-switched multiterminal junction realized in a single conducting plane is exploited as a nanoelectronic half-adder. Our results demonstrate that self-switching effects may be used to increase the functionality of a given number of nanoelectronic devices. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents an inductive coupling technique to investigate edge magnetoplasmons (EMP) in two-dimensional electron gases in the time domain. Manifestation on time delay, amplitude, and broadening of EMP as function of magnetic field; Observation of a narrowing of response peak; Decrease of the EMP dispersion.