Non-perturbative Correlation Effects in Diluted Magnetic Semiconductors

The effects of carrier-impurity correlations due to a Kondo-like spin-spin interaction in diluted magnetic semiconductors are investigated. These correlations are not only responsible for a transfer of spins between the carriers and the impurities, but also produce non-perturbative effects in the spin dynamics such as renormalization of the precession frequency of the carrier spins, which can reach values of several percent in CdMnTe quantum wells. In two-dimensional systems, the precession frequency renormalization for a single electron spin with defined wave vector shows logarithmic divergences similar to those also known from the Kondo problem in metals. For smooth electron distributions, however, the divergences disappear due to the integrability of the logarithm. A possible dephasing mechanism caused by the wave-vector dependence of the electron spin precession frequencies is found to be of minor importance compared to the spin transfer from the carrier to the impurity system. In the Markov limit of the theory, a quasi-equilibrium expression for the carrier-impurity correlation energy can be deduced indicating the formation of strongly correlated carrier-impurity states for temperatures in the mK range

Quantum correlations of a two-dimensional electron gas with Rashba spin-orbit coupling

We study the correlations of a two-dimensional electron gas with Rashba spin-orbit coupling (SOC). We obtain the two-particle density matrix and use it to derive the exchange hole. We find a nontrivial correlation for electrons with opposite spin projections that does not occur without Rashba SOC. The two-particle density matrix allows us to further study the quantum correlations of the system. We use it to obtain the concurrence and the entanglement of formation in order to quantify the entanglement of the electron spins. Additionally, we calculate the quantum discord and compare it with the entanglement and classical correlations.Fil: Aranzadi, J. I.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: Tamborenea, Pablo Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin

Narrow quantum rings with general Rashba and Dresselhaus spin-orbit interactions

We solve the energy eigenvalue problem of narrow semiconductor quantum rings including the Rashba and Dresselhaus spin-orbit interactions with general coupling constants. We show that the eigenstates of the system can be expressed as products of a scalar Mathieu function and a spinor function which is either periodic or pseudo-periodic on the ring coordinate. The spinor functions are solutions to an ordinary differential equation on the ring coordinate which is analogous to the time-dependent Schrödinger equation. The eigenenergies of the ring correspond to the eigenvalues of the Mathieu function. For realistic material parameters, satisfactory analytical solutions can be obtained using standard approximations. Our solution method can be applied to quantum rings with a general linear-in-k spin-orbit interactions.Fil: Lia, J.M.. Universidad de Buenos Aires; ArgentinaFil: Tamborenea, Pablo Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin

Electronic transitions in disk-shaped quantum dots induced by twisted light

We theoretically investigate the absorption and emission of light carrying orbital angular momentum (twisted light) by quasi-two-dimensional (disk-shaped) quantum dots in the presence of a static magnetic field. We calculate the transition matrix element for the light-matter interaction and use it to explore different scenarios, depending on the initial and final states of the electron undergoing the optically induced transition. We make explicit the selection rule for the conservation of the z projection of the orbital angular momentum. For a realistic set of parameters (quantum dot size, beam waist, photon energy, etc.) the strength of the transition induced by twisted light is 10% of that induced by plane waves. Finally, our analysis indicates that it may be possible to select precisely the electronic level one wishes to populate using the appropriate combination of light-beam parameters suggesting technological applications to the quantum control of electronic states in quantum dots. © 2009 The American Physical Society.Fil: Quinteiro, Guillermo Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Tamborenea, Pablo Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin

Level structure and spin-orbit effects in quasi-one-dimensional semiconductor nanostructures

We investigate theoretically how the spin-orbit Dresselhaus and Rashba effects influence the electronic structure of quasi-one-dimensional semiconductor quantum dots, similar to those that can be formed inside semiconductor nanorods. We calculate electronic energy levels, eigenfunctions, and effective g-factors for coupled, double dots made out of different materials, especially GaAs and InSb. We show that by choosing the form of the lateral confinement, the contributions of the Dresselhaus and Rashba terms can be tuned and suppressed, and we consider several possible cases of interest. We also study how, by varying the parameters of the double-well confinement in the longitudinal direction, the effective g-factor can be controlled to a large extent.Fil: Romano, Carla Lidia. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Ulloa Cornejo, Patricia Silvia Elizabeth. Ohio University; Estados UnidosFil: Tamborenea, Pablo Ignacio. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin

Interplay between optical vortices and condensed matter

Interest in the multiple facets of optical vortices has flourished in the last three decades. This review examines the basic research and applications of the interplay between optical vortices and condensed-matter systems. This subfield of optical-vortex physics has rapidly developed in recent years thanks to a vigorous synergy between theory and experiment. After presenting self-contained and focused introductions to optical vortices and condensed-matter optics, theory and current progress in the research on the interaction of condensed-matter systems and optical vortices are examined. When one considers the interaction of optical vortices with condensed-matter systems, many aspects of the standard theory of the interaction of matter with plane-wave light need to be reformulated. In bulk, light-matter Hamiltonian matrix elements have to be recalculated and novel selection rules are obtained, reflecting the conservation of total angular momentum. Orbital angular momentum is transferred from the light beam to the photoexcited electrons, thereby generating macroscopic currents. Semiconductor nanostructures add the complexity of their own spatial inhomogeneity, which is handled adequately by the envelope-function approximation. Here again modified matrix elements for light-matter interactions dictate the allowed and forbidden optical transitions, which are distinct from those obtained in traditional optical excitation with smooth fields. Quantum rings play a central role due to their specially adapted geometry to the cylindrical nature of the optical-vortex beams. When the electron-electron interaction is taken into account, the rich physics of excitons and exciton polaritons comes into play and is modified by the finite orbital angular momentum of the structured light. Furthermore, the new features brought about by optical vortices in plasmonics and in the optical excitation of two-dimensional materials are reviewed. For all these systems theory and recent experiments are discussed. Finally, an overview of current and prospective applications of the interaction of optical vortices with condensed-matter systems in the fields of quantum technologies, communications, sensing, etc., is presented. Throughout this review an attempt has been made to present not only a survey of the relevant literature but also a perspective on the interesting and rapidly evolving field of optical-vortex-condensed-matter interactions.Fil: Quinteiro, Guillermo Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Modelado e Innovación Tecnológica. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Modelado e Innovación Tecnológica; ArgentinaFil: Tamborenea, Pablo Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Kuhn, Tilmann. Westfälische Wilhelms Universität; Alemani

Anisotropic magnetoresistivity in structured elastomer composites: modelling and experiments

A constitutive model for the anisotropic magnetoresistivity in structured elastomer composites (SECs) is proposed. The SECs considered here are oriented pseudo-chains of conductive-magnetic inorganic materials inside an elastomer organic matrix. The pseudo-chains are formed by fillers which are simultaneously conductive and magnetic dispersed in the polymer before curing or solvent evaporation. The SEC is then prepared in the presence of a uniform magnetic field, referred to as Hcuring. This procedure generates the pseudo-chains, which are preferentially aligned in the direction of Hcuring. Electrical conduction is present in that direction only. The constitutive model for the magnetoresistance considers the magnetic pressure, Pmag, induced on the pseudo-chains by an external magnetic field, H, applied in the direction of the pseudo-chains. The relative changes in conductivity as a function of H are calculated by evaluating the relative increase of the electron tunnelling probability with Pmag, a magneto-elastic coupling which produces an increase of conductivity with magnetization. The model is used to adjust experimental results of magnetoresistance in a specific SEC where the polymer is polydimethylsiloxane, PDMS, and fillers are microparticles of magnetite?silver (referred to as Fe3O4[Ag]). Simulations of the expected response for other materials in both superparamagnetic and blocked magnetic states are presented, showing the influence of the Young´s modulus of the matrix and filler´s saturation magnetization.Fil: Mietta, J. L.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; ArgentinaFil: Tamborenea, Pablo Ignacio. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Negri, Ricardo Martin. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentin

Spin dynamics of hot excitons in diluted magnetic semiconductors with spin-orbit interaction

We explore the impact of a Rashba-type spin-orbit interaction in the conduction band on the spin dynamics of hot excitons in diluted magnetic semiconductor quantum wells. In materials with strong spin-orbit coupling, we identify parameter regimes where spin-orbit effects greatly accelerate the spin decay and even change the dynamics qualitatively in the form of damped oscillations. Furthermore, we show that the application of a small external magnetic field can be used to either mitigate the influence of spin-orbit coupling or entirely remove its effects for fields above a material-dependent threshold.Fil: Ungar, F.. University of Bayreuth; AlemaniaFil: Tamborenea, Pablo Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Axt, V. M.. University of Bayreuth; Alemani

Orbital and spin dynamics of intraband electrons in quantum rings driven by twisted light

We theoretically investigate the effect that twisted light has on the orbital and spin dynamics of electrons in quantum rings possessing sizable Rashba spin-orbit interaction. The system Hamiltonian for such a strongly inhomogeneous light field exhibits terms which induce both spin-conserving and spin-flip processes. We analyze the dynamics in terms of the perturbation introduced by a weak light field on the Rasha electronic states, and describe the effects that the orbital angular momentum as well as the inhomogeneous character of the beam have on the orbital and the spin dynamics. © 2011 Optical Society of America.Fil: Quinteiro, Guillermo Federico. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Tamborenea, Pablo Ignacio. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Berakdar, J.. Universitaet Halle; Alemani