Добірка наукової літератури з теми "Q2DEG"

The interface between two wide band-gap insulators, LaAlO3 and SrTiO3 (LAO/STO), hosts a quasi-two-dimensional electron gas (q2DEG), two-dimensional superconductivity, ferromagnetism, and giant Rashba spin-orbit coupling. The co-existence of two-dimensional superconductivity with gate-tunable spin-orbit coupling and multiband occupation is of particular interest for the realization of unconventional superconducting pairing. To investigate the symmetry of the superconducting order parameter, phase sensitive measurements of the Josephson effect are required. We describe an approach for the fabrication of artificial superconducting weak links at the LAO/STO interface using direct high-resolution electron beam lithography and low-energy argon ion beam irradiation. The method does not require lift-off steps or sacrificial layers. Therefore, resolution is only limited by the electron beam lithography and pattern transfer. We have realized superconducting weak links with a barrier thickness of 30–100 nm. The barrier transparency of the weak links can be controlled by the irradiation dose and further tuned by a gate voltage. Our results open up new possibilities for the realization of quantum devices in oxide interfaces.

In organic electronics, conjugated conductive polymers are most widely used. The scope of their application is currently very wide. Non-conjugated polymers are used much less in electronics and are usually used as insulation materials or materials for capacitors. However, the potential of non-conjugated polymers is much wider, due to the fact that new electronic materials with unique electronic properties can be created on the basis of non-conjugated polymers, as well as other inorganic dielectrics. This article demonstrates the possibilities of creating electrically conductive materials with unique electronic parameters based on non-conjugated polymers. The results of the study of the sensory properties of humidity are given as examples of the practical application of the structure. The abnormal electronic properties are realized along the interface of two polymer dielectrics with functional polar groups. The submicron films of polydiphenylenephthalide were used as a dielectric. It is shown that a quasi-two-dimensional electronic structure with abnormally large values of conductivity and mobility of charge carriers occurs along the interface. These structures are often called quasi-two-dimensional electron gas (Q2DEG). This article describes the manufacturing processes of multielectrode devices. Polymer films are deposited via the spin-coating method with polymer solutions in cyclohexanone. The metal electrodes were manufactured through thermal deposition in a vacuum. Three types of metal electrodes made of aluminum, copper and chromium were used. The influence of the electron work function of contacting metals on the electronic parameters of the structure was studied. It was established that the work function decrease leads to an increase in the conductivity and mobility of charge carriers. The charge carrier parameters were estimated based on the analysis of the current-voltage characteristics within the space-charge-limited current technique. The Richardson-Schottky thermionic emission model was used to evaluate values a potential barrier at metal/organic interfaces. It was established that the change in ambient humidity strongly affects the electronic transport properties along the polymer/polymer interface. It is demonstrated that the increase in conductivity with an increase in humidity occurs due to an increase in the mobility of charge carriers and a decrease in the height of the potential barrier at the three-dimensional metal contact with two-dimensional polymer interface. The potential barrier between the electrode and the bulk of the polymer film is significantly higher than between the electrode and the quasi-two-dimensional polymer structure.

The dynamics of a quasi-two-dimensional electron system (q2DES) in the presence of a tilted magnetic field is reconsidered employing the thin-layer method. We derive the effective equations for relativistic and nonrelativistic q2DESs. Through a perturbative expansion, we show that while the magnetic length is much greater than the confinement width, the in-plane magnetic field only affects the particle dynamics through the spin. Therefore, effects due to an in-plane magnetic vector potential reported previously in the literature for 2D quantum rings, 2D quantum dots and graphene are fictitious. In particular, the so-called pseudo chiral magnetic effect recently proposed in graphene is not realistic.

Data from the Census Bureau's Annual Report on Poverty show that 37.4 million Americans—two million more than the previous year—had no health insurance during 1992. The proportion of people with no health insurance also increased from 14.1 percent in 1991 to 14.7 percent in 1992. This is the largest annual increase—both in the number of people and the proportion of the population lacking health care coverage—since 1987, the first year for which comparable data are available. In 1987, the Census data show, 31 million people—12.9 percent of the population—were not covered by health insurance. Both the number of people and the proportion of the population without health insurance have increased each year since 1987. Not all of the changes from one year to the next were statistically significant. Between 1991 and 1992, however, the increases both in the number of people without insurance and the proportion of the population lacking insurance were statistically significant. The Bureau reported that 36.9 million Americans were poor in 1992, which represented the largest number of poor people in 30 years. Among the poor, 28.5 percent had no health insurance in 1992. Lack of insurance was not limited to the poor, however. Of those without insurance in 1992, more than 70 percent were above the poverty line.

AbstractMulti-orbital physics in quasi-two-dimensional electron gases (q2DEGs) triggers intriguing phenomena not observed in bulk materials, such as unconventional superconductivity and magnetism. Here, we investigate the mechanism of orbital selective switching of the spin-polarization in the oxide q2DEG formed at the (001) interface between the LaAlO3, EuTiO3 and SrTiO3 band insulators. By using density functional theory calculations, transport, magnetic and x-ray spectroscopy measurements, we find that the filling of titanium-bands with 3dxz/3dyz orbital character in the EuTiO3 layer and at the interface with SrTiO3 induces an antiferromagnetic to ferromagnetic switching of the exchange interaction between Eu-4f7 magnetic moments. The results explain the observation of the carrier density-dependent ferromagnetic correlations and anomalous Hall effect in this q2DEG, and demonstrate how combined theoretical and experimental approaches can lead to a deeper understanding of emerging electronic phases and serve as a guide for the materials design of advanced electronic applications.

The ratio of the scattering and single-particle relaxation time of a quasi-two-dimensional electron gas (Q2DEG) in a finite lattice-mismatched GaAs/InGaAs/GaAs quantum well was investigate at zero and finite temperatures, taking into account the exchange-correlation effects via a local-field correction with three approximations for the LFC, G = 0, GH, and GGA. We studied the dependence of the surface roughness, roughness-induced piezoelectric, remote and homogenous background charged impurity scattering on the carrier density and quantum well width. In the case of zero temperature and Hubbard local-field correction our results reduced to those of different theoretical calculations. At low density, the exchange-correlation effects depend strongly on the ratio τt/τs. While at high density many-body effects due to exchange and correlation considerably modified the ratio of the scattering and single-particle relaxation time. We found that, for densities and temperatures considered T = 0,3TF in this study, the temperature affected weakly on the time ratio for four scatterings. Furthermore, with the change of quantum well width, the effect of LFC and temperatures act on the ratio τt/τs are negligible for the roughness-induced piezoelectric and remote charged impurity scattering, and are notable for the surface roughness and homogenous background charged impurity scattering.

In condensed matter physics, the concepts of topology and symmetry are of paramount importance, particularly in understanding quantum phase transitions. Topology classifies objects based on their topological properties, which are properties that are preserved under continuous deformation. This is relevant to a wide range of phenomena, such as topological insulators and the quantum Hall effect. On the other hand, symmetry is used to understand phase transitions, where a higher symmetry group is broken into a lower symmetry subgroup. The study of quantum phases and phase transitions is a fundamental theme in condensed matter physics, and topology and symmetry play a critical role in comprehending these phenomena. This field of research is vital in understanding the behavior of matter at the quantum level and has potential applications in quantum computing and other technologies This thesis mainly explored the quantum phase transitions through resistance fluctuation spectroscopy. The first part of the thesis focused on uncovering the electronic phases in 1T-TaS2 . The presence of a low temperature insulating phase in 1T-TaS2 has been a matter of debate among researchers, with recent theoretical calculations suggesting that it is a result of out-of-plane stacking rather than a Mott insulator Our findings suggest that out-of-plane stacking might be responsible for the observed insulating phase at low temperatures. Our study showed that the device exhibited metallic behavior at low temperatures, but an insulating phase was restored over a narrow range as the temperature increased. The system also exhibited signs of electrical phase separation prior to the restoration of the insulating phase, as seen through quantized jumps in conductance between two well-defined levels. These jumps were speculated to result from metallic domain walls separating insulating regions. In the second part of the thesis, we studied the resistance fluctuations near the Lifshitz transition in WTe2 using electrical and thermal transport studies. The presence of two holes and two electron pockets in the band structure at low temperatures and the disappearance of the hole pockets above the transition temperature could be related to a topological phase transition in the material. An electrical noise peak was observed at the transition temperature, which was attributed to inter-band scattering at Weyl points. The study emphasized the importance of high-quality samples for detecting the unique properties of Weyl semi-metals. In the final section of the thesis, the behavior of charge dynamics in a quasi-two-dimensional electron gas (q2DEG) at the LaScO3/SrTiO3 interface was studied through resistance fluctuation spectroscopy. Despite persistent efforts, the source of charge carriers at the oxide interface remains elusive. [7, 8, 9]. Our study indicated that the role of oxygen vacancies in transport properties at the oxide interface requires further exploration. The q2DEG at the LaScO3/SrTiO3 interface was found to exhibit random telegraphic noise (RTN) at high temperatures, which disappeared below 40 K, indicating a temperature-dependent behavior of the charge dynamics. Based on these observations, we posit that the RTN is likely the result of charge exchange between mid-gap defect states in the bulk and the q2DEG.