Weak localization of holes in high-mobility heterostructures

Theory of weak localization is developed for two-dimensional holes in semiconductor heterostructures. Ballistic regime of weak localization where the backscattering occurs from few impurities is studied with account for anisotropic momentum scattering of holes. The transition from weak localization to anti-localization is demonstrated for long dephasing times. For stronger dephasing the conductivity correction is negative at all hole densities due to non-monotonous dependence of the spin relaxation time on the hole wavevector. The anomalous temperature dependent correction to the conductivity is calculated. We show that the temperature dependence of the conductivity is non-monotonous at moderate hole densities.Comment: 5 pages, 4 figure

Spin-orbit interaction and weak localization in heterostructures

Theory of weak localization in two-dimensional high-mobility semiconductor systems is developed with allowance for the spin-orbit interaction. The obtained expressions for anomalous magnetoresistance are valid in the whole range of classically weak magnetic fields and for arbitrary strengths of bulk and structural inversion asymmetry contributions to the spin splitting. The theory serves for both diffusive and ballistic regimes of electron propagation taking into account coherent backscattering and nonbackscattering processes. The transition between weak localization and antilocalization regimes is analyzed. The manifestation of the mutual compensation of Rashba and Dresselhaus spin splittings in magnetoresistance is discussed. Perfect description of experimental data on anomalous magnetoresistance in high-mobility heterostructures is demonstrated. The in-plane magnetic field dependence of the conductivity caused by an interplay of the spin-orbit splittings and Zeeman effect is described theoretically.Comment: Review for the special issue of Semicond. Sci. Technol. "The effects of spin-orbit interaction on charge transport". 8 pages, 5 figure

Pion-nucleon scattering in covariant baryon chiral perturbation theory with explicit Delta resonances

We present the results of a third order calculation of the pion-nucleon scattering amplitude in a chiral effective field theory with pions, nucleons and delta resonances as explicit degrees of freedom. We work in a manifestly Lorentz invariant formulation of baryon chiral perturbation theory using dimensional regularization and the extended on-mass-shell renormalization scheme. In the delta resonance sector, the on mass-shell renormalization is realized as a complex-mass scheme. By fitting the low-energy constants of the effective Lagrangian to the $S$- and $P$-partial waves a satisfactory description of the phase shifts from the analysis of the Roy-Steiner equations is obtained. We predict the phase shifts for the $D$ and $F$ waves and compare them with the results of the analysis of the George Washington University group. The threshold parameters are calculated both in the delta-less and delta-full cases. Based on the determined low-energy constants, we discuss the pion-nucleon sigma term. Additionally, in order to determine the strangeness content of the nucleon, we calculate the octet baryon masses in the presence of decuplet resonances up to next-to-next-to-leading order in SU(3) baryon chiral perturbation theory. The octet baryon sigma terms are predicted as a byproduct of this calculation.Comment: 41 pages, 12 figures, 7 table

Tvorba eta mezona u nn sudarima

A model calculation for near-threshold η meson production in nucleon-nucleon collisions is presented. The η meson production is described by elementary rescattering processes via MN→ ηN, with M = π, ρ, η and σ. Corresponding amplitudes are taken from a multi-channel meson-exchange model of the πN system developed by the Jülich group. Effects of the NN interaction in the final as well as in the initial state are taken into account microscopically.Predstavljamo model za računanje tvorbe η mezona blizu praga u sudarima nukleon-nukleon. Tvorba η mezona opisuje se elementarnim procesima ponovnog raspršenja putem MN→ ηN, sa M = π, ρ, η i σ. Odnosne amplitude uzimaju se od višekanalnog modela izmjene mezona u sustavu πN koji je razvila grupa u Jülichu. Učinci međudjelovanja u konačnom stanju kao i u početnom stanju uzeti su u obzir mikroskopski

Tvorba eta mezona u nn sudarima

A model calculation for near-threshold η meson production in nucleon-nucleon collisions is presented. The η meson production is described by elementary rescattering processes via MN→ ηN, with M = π, ρ, η and σ. Corresponding amplitudes are taken from a multi-channel meson-exchange model of the πN system developed by the Jülich group. Effects of the NN interaction in the final as well as in the initial state are taken into account microscopically.Predstavljamo model za računanje tvorbe η mezona blizu praga u sudarima nukleon-nukleon. Tvorba η mezona opisuje se elementarnim procesima ponovnog raspršenja putem MN→ ηN, sa M = π, ρ, η i σ. Odnosne amplitude uzimaju se od višekanalnog modela izmjene mezona u sustavu πN koji je razvila grupa u Jülichu. Učinci međudjelovanja u konačnom stanju kao i u početnom stanju uzeti su u obzir mikroskopski

Extraction of scattering lengths from final-state interactions

A recently proposed method based on dispersion theory, that allows to extract the scattering length of a hadronic two-body system from corresponding final-state interactions, is generalized to the situation where the Coulomb interaction is present. The steps required in a concrete practical application are discussed in detail. In addition a thorough examination of the accuracy of the proposed method is presented and a comparison is made with results achieved with other methods like the Jost-function approach based on the effective-range approximation. Deficiencies of the latter method are pointed out. The reliability of the dispersion theory method for extracting also the effective range is investigated.Comment: 16 pages, 6 figures, some corrections to text, to appear in Phys. Rev.

Exclusive and semi-inclusive strangeness and charm production in πN\pi N and NNNN reactions

Using the Quark-Gluon Strings Model (QGSM) combined with Regge phenomenology we consider the reactions $\pi^- p \to K^0 \Lambda$ and $\pi^- p \to D^- \Lambda_c^+$ which are dominated by the contributions of the $K^*$ and $D^*$ Regge trajectories, respectively. The spin structure of the amplitudes is described by introducing Reggeized Born terms. It is found that the existing data for the reaction $\pi^- p \to K^0 \Lambda$ are in reasonable agreement with the model predictions. To describe the absolute values of the cross sections it is necessary to introduce also suppression factors which can be related to absorption corrections. Furthermore, assuming the SU(4) symmetry to hold for Regge residues and the universality of absorption corrections we calculate the cross section of the reaction $\pi^- p \to D^- \Lambda_c^+$. Employing the latter results from $\pi^- p$ reactions we then estimate the contributions of the pion exchange mechanism to the cross sections of the reactions $NN \to NK\Lambda$ and $NN \to N\bar D \Lambda_c$ and compare them with the contributions of the $K$ and $D$ exchanges. We find that the $NN$ reactions are dominated not by pion exchange but by $K$ and $D$ exchanges, respectively. Moreover, assuming the SU(4) symmetry to hold approximately for the coupling constants $g_{ND \Lambda_c}$ = $g_{NK \Lambda}$ we analyze also the production of leading $\Lambda_c$ hyperons in the reaction $NN \to \Lambda_c X$. It is shown that the non-perturbative mechanism should give an essential contribution to the $\Lambda_c$ yield for $x \geq 0.5$.Comment: 3 pages, LaTeX, 4 postscript figures; contribution to QNP2002, Juelich, June 10-14, 200