Room temperature coherent spin alignment of silicon vacancies in 4H- and 6H-SiC

We report the realization of the optically induced inverse population of the ground-state spin sublevels of the silicon vacancies ($V_{\mathrm{Si}}$) in silicon carbide (SiC) at room temperature. The data show that the probed silicon vacancy spin ensemble can be prepared in a coherent superposition of the spin states. Rabi nutations persist for more than 80 $\mu$s. Two opposite schemes of the optical alignment of the populations between the ground-state spin sublevels of the silicon vacancy upon illumination with unpolarized light are realized in 4H- and 6H-SiC at room temperature. These altogether make the silicon vacancy in SiC a very favorable defect for spintronics, quantum information processing, and magnetometry.Comment: 4 pages, 3 picture

The multiplicity and the spectra of secondaries correlated with the leading particle energy

The spectra of leading particles of different nature in pp-collisions at E sub 0 = 33 GeV are obtained. The multiplicities and the spectra of secondaries, mesons, gamma-quanta, lambda and lambda-hyperons and protons for different leading particle energy ranges are determined

Interactions in high-mobility 2D electron and hole systems

Electron-electron interactions mediated by impurities are studied in several high-mobility two-dimensional (electron and hole) systems where the parameter $k_BT\tau /\hbar$ changes from 0.1 to 10 ($\tau$ is the momentum relaxation time). This range corresponds to the \textit{intermediate} and \textit {ballistic} regimes where only a few impurities are involved in electron-electron interactions. The interaction correction to the Drude conductivity is detected in the temperature dependence of the resistance and in the magnetoresistance in parallel and perpendicular magnetic fields. The effects are analysed in terms of the recent theories of electron interactions developed for the ballistic regime. It is shown that the character of the fluctuation potential (short-range or long-range) is an important factor in the manifestation of electron-electron interactions in high-mobility 2D systems.Comment: 22 pages, 11 figures; to appear in proceedings of conference "Fundamental Problems of Mesoscopic Physics", Granada, Spain, 6-11 September, 200

On the Electron-Electron Interactions in Two Dimensions

In this paper, we analyze several experiments that address the effects of electron-electron interactions in 2D electron (hole) systems in the regime of low carrier density. The interaction effects result in renormalization of the effective spin susceptibility, effective mass, and g*-factor. We found a good agreement among the data obtained for different 2D electron systems by several experimental teams using different measuring techniques. We conclude that the renormalization is not strongly affected by the material or sample-dependent parameters such as the potential well width, disorder (the carrier mobility), and the bare (band) mass. We demonstrate that the apparent disagreement between the reported results on various 2D electron systems originates mainly from different interpretations of similar "raw" data. Several important issues should be taken into account in the data processing, among them the dependences of the effective mass and spin susceptibility on the in-plane field, and the temperature dependence of the Dingle temperature. The remaining disagreement between the data for various 2D electron systems, on one hand, and the 2D hole system in GaAs, on the other hand, may indicate more complex character of electron-electron interactions in the latter system.Comment: Added refs; corrected typos. 19 pages, 7 figures. To be published in: Chapter 19, Proceedings of the EURESCO conference "Fundamental Problems of Mesoscopic Physics ", Granada, 200

In-plane Magnetoconductivity of Si-MOSFET's: A Quantitative Comparison between Theory and Experiment

For densities above $n=1.6 \times 10^{11}$ cm$^{-2}$ in the strongly interacting system of electrons in two-dimensional silicon inversion layers, excellent agreement between experiment and the theory of Zala, Narozhny and Aleiner is obtained for the response of the conductivity to a magnetic field applied parallel to the plane of the electrons. However, the Fermi liquid parameter $F_0^\sigma(n)$ and the valley splitting $\Delta_V(n)$ obtained from fits to the magnetoconductivity, although providing qualitatively correct behavior (including sign), do not yield quantitative agreement with the temperature dependence of the conductivity in zero magnetic field. Our results suggest the existence of additional scattering processes not included in the theory in its present form

Effects of Electron-Electron and Electron-Phonon Interactions in Weakly Disordered Conductors and Heterostuctures

We investigate quantum corrections to the conductivity due to the interference of electron-electron (electron-phonon) scattering and elastic electron scattering in weakly disordered conductors. The electron-electron interaction results in a negative $T^2 \ln T$-correction in a 3D conductor. In a quasi-two-dimensional conductor, $d < v_F/T$ ($d$ is the thickness, $v_F$ is the Fermi velocity), with 3D electron spectrum this correction is linear in temperature and differs from that for 2D electrons (G. Zala et. al., Phys. Rev.B {\bf 64}, 214204 (2001)) by a numerical factor. In a quasi-one-dimensional conductor, temperature-dependent correction is proportional to $T^2$. The electron interaction via exchange of virtual phonons also gives $T^2$-correction. The contribution of thermal phonons interacting with electrons via the screened deformation potential results in $T^4$-term and via unscreened deformation potential results in $T^2$-term. The interference contributions dominate over pure electron-phonon scattering in a wide temperature range, which extends with increasing disorder.Comment: 6 pages, 2figure

The metallic resistance of a dilute two-dimensional hole gas in a GaAs quantum well: two-phase separation at finite temperature?

We have studied the magnetotransport properties of a high mobility two-dimensional hole gas (2DHG) system in a 10nm GaAs quantum well (QW) with densities in range of 0.7-1.6*10^10 cm^-2 on the metallic side of the zero-field 'metal-insulator transition' (MIT). In a parallel field well above B_c that suppresses the metallic conductivity, the 2DHG exhibits a conductivity g(T)~0.3(e^2/h)lnT reminiscent of weak localization. The experiments are consistent with the coexistence of two phases in our system: a metallic phase and a weakly insulating Fermi liquid phase having a percolation threshold close to B_c

Hole-hole interaction effect in the conductance of the two-dimensional hole gas in the ballistic regime

On a high-mobility two-dimensional hole gas (2DHG) in a GaAs/GaAlAs heterostructure we study the interaction correction to the Drude conductivity in the ballistic regime, k(B)Ttau/(h) over bar >1. It is shown that the "metallic" behavior of the resistivity (drho/dT>0) of the low-density 2DHG is caused by the hole-hole interaction effect in this regime. We find that the temperature dependence of the conductivity and the parallel-field magnetoresistance are in agreement with this description, and determine the Fermi-liquid interaction constant F-0(sigma) which controls the sign of drho/dT