Spin-polarized half-metallic state of a ferromagnetic δ layer in a semiconductor host

We discuss a model which is apt to describe the appearance of a spin-polarized half-metallic state around a single δ layer of a magnetic transition metal embedded into a nonmagnetic semiconductor host. We show that ferromagnetism in this system can be attributed to the intrinsic physical properties of the δ layer. The relevant physical effects described by our model are the hybridization of the electron states of the metal and semiconductor atoms, the charge redistribution around the δ layer, and the electron-electron correlation on a metal atom, which is the driving force of ferromagnetism. We obtain the mean-field phase diagram of the model at zero and finite temperature, both in the case when the chemical potential is fixed, and when the density of particles on the δ layer is fixed. The relevance of our results in connection with numerical and experimental results on the so-called digital magnetic heterostructures, in the absence and in the presence of a quantum-well carrier channel, is eventually discussed. © 2011 American Physical Society.Peer Reviewe

Band bending driven evolution of the bound electron states at the interface between a three-dimensional topological insulator and a three-dimensional normal insulator

In the frame of k⋅p method and variational approach for the effective energy functional of a contact between a three-dimensional topological insulator (TI) and normal insulator (NI), we analytically describe the formation of interfacial bound electron states of two types (ordinary and topological) having different spatial distributions and energy spectra. We show that these states appear as a result of the interplay of two factors: hybridization and band bending of the TI and NI electron states near the TI/NI boundary. These results are corroborated by the density functional theory calculations for the exemplar Bi2Se3/ZnSe system

Magnetic proximity effect at the 3D topological insulator/magnetic insulator interface

The magnetic proximity effect is a fundamental feature of heterostructures composed of layers of topological insulators and magnetic materials since it underlies many potential applications in devices with novel quantum functionality. Within density functional theory we study magnetic proximity effect at the 3D topological insulator/magnetic insulator (TI/MI) interface in Bi$_2$Se$_3$/MnSe(111) system as an example. We demonstrate that a gapped ordinary bound state which spectrum depends on the interface potential arises in the immediate region of the interface. The gapped topological Dirac state also arises in the system owing to relocation to deeper atomic layers of topological insulator. The gap in the Dirac cone is originated from an overlapping of the topological and ordinary interfacial states. This result being also corroborated by the analytic model, is a key aspect of the magnetic proximity effect mechanism in the TI/MI structures.Comment: 10 pages, 3 figure

Pecularities of Hall effect in GaAs/{\delta}<Mn>/GaAs/In\timesGa1-\timesAs/GaAs (\times {\approx} 0.2) heterostructures with high Mn content

Transport properties of GaAs/{\delta}/GaAs/In\timesGa1-\timesAs/GaAs structures containing InxGa1-xAs (\times {\approx} 0.2) quantum well (QW) and Mn delta layer (DL) with relatively high, about one Mn monolayer (ML) content, are studied. In these structures DL is separated from QW by GaAs spacer with the thickness ds = 2-5 nm. All structures possess a dielectric character of conductivity and demonstrate a maximum in the resistance temperature dependence Rxx(T) at the temperature {\approx} 46K which is usually associated with the Curie temperature Tc of ferromagnetic (FM) transition in DL. However, it is found that the Hall effect concentration of holes pH in QW does not decrease below TC as one ordinary expects in similar systems. On the contrary, the dependence pH(T) experiences a minimum at T = 80-100 K depending on the spacer thickness, then increases at low temperatures more strongly than ds is smaller and reaches a giant value pH = (1-2)\cdot10^13 cm^(-2). Obtained results are interpreted in the terms of magnetic proximity effect of DL on QW, leading to induce spin polarization of the holes in QW. Strong structural and magnetic disorder in DL and QW, leading to the phase segregation in them is taken into consideration. The high pH value is explained as a result of compensation of the positive sign normal Hall effect component by the negative sign anomalous Hall effect component.Comment: 19 pages, 6 figure

Noise studies of magnetization dynamics in dilute magnetic semiconductor heterostructures

We study theoretically and experimentally the frequency and temperature dependence of resistivity noise in semiconductor heterostructures delta-doped by Mn. The resistivity noise is observed to be non-monotonous as a function of frequency. As a function of temperature, the noise increases by two orders of magnitude for a resistivity increase of about 50%. We study two possible sources of resistivity noise -- dynamic spin fluctuations and charge fluctuations, and find that dynamic spin fluctuations are more relevant for the observed noise data. The frequency and temperature dependence of resistivity noise provide important information on the nature of the magnetic interactions. In particular, we show how noise measurements can help resolve a long standing debate on whether the Mn-doped GaAs is an p-d Zener/RKKY or double exchange ferromagnet. Our analysis includes the effect of different kinds of disorder such as spin-glass type of interactions and a site-dilution type of disorder. We find that the resistivity noise in these structures is well described by a disordered RKKY ferromagnet model dynamics with a conserved order parameter.Comment: 15 pages, 7 eps figures, published versio

Orthopaedic treatment of patients using the device to determine and fix the central bite

A large number of errors, which often occur in prosthodontics in prosthetics patients with non-fixed bite, mainly related to the quality of the determination and the central Bite. Violation of the natural position of the mandible leads to a pathological condition in a patient from the TMJ and masticatory muscles goal of our work was the development and application of new devices for the measurement and recording centric relation jaw. Proper identification and recording centric relation jaw can improve the quality of prosthetic patients in terms of functional value of dentures and accelerate the process of adaptation of patients to removable dentures.Большое количество ошибок, которые часто встречаются в практике ортопедической стоматологии при протезировании больных с нефиксированным прикусом, связаны в основном с качеством определения и фиксации центрального соотношения челюстей. Нарушение естественного положения нижней челюсти приводит к возникновению патологических состояний у пациента со стороны височно-нижнечелюстного сустава и жевательной мускулатуры. Целью нашей работы явилось разработка и применение нового устройства для определения и фиксации центрального соотношения челюстей. Правильное определение и фиксация центрального соотношения челюстей позволяет повысить качество протезирования пациентов с точки зрения функциональной ценности съемных протезов и ускорить процесс адаптации больных к съемным протезам