Optical properties of 1D photonic crystals based on multiple-quantum-well structures

A general approach to the analysis of optical properties of photonic crystals based on multiple-quantum-well structures is developed. The effect of the polarization state and a non-perpendicular incidence of the electromagnetic wave is taken into account by introduction of an effective excitonic susceptibility and an effective optical width of the quantum wells. This approach is applied to consideration of optical properties of structures with a pre-engineered break of the translational symmetry. It is shown, in particular, that a layer with different exciton frequency placed at the middle of an MQW structure leads to appearance of a resonance suppression of the reflection.Comment: 9 pages, 3 figures, submitted to PR

Valley Dependent Optoelectronics from Inversion Symmetry Breaking

Inversion symmetry breaking allows contrasted circular dichroism in different k-space regions, which takes the extreme form of optical selection rules for interband transitions at high symmetry points. In materials where band-edges occur at noncentral valleys, this enables valley dependent interplay of electrons with light of different circular polarizations, in analogy to spin dependent optical activities in semiconductors. This discovery is in perfect harmony with the previous finding of valley contrasted Bloch band features of orbital magnetic moment and Berry curvatures from inversion symmetry breaking [Phys. Rev. Lett. 99, 236809 (2007)]. A universal connection is revealed between the k-resolved optical oscillator strength of interband transitions, the orbital magnetic moment and the Berry curvatures, which also provides a principle for optical measurement of orbital magnetization and intrinsic anomalous Hall conductivity in ferromagnetic systems. The general physics is demonstrated in graphene where inversion symmetry breaking leads to valley contrasted optical selection rule for interband transitions. We discuss graphene based valley optoelectronics applications where light polarization information can be interconverted with electronic information.Comment: Expanded version, to appear in Phys. Rev.

Comment on ``Spin and cyclotron energies of electrons in GaAs/GaAlAs quantum wells''

In a recent publication, Pfeffer and Zawadzki [cond-mat/0607150; Phys. Rev. B 74, 115309 (2006)] attempted a calculation of electron g factor in III-V heterostructures. The authors emphasize that their outcome is in strong discrepancy with our original result [Ivchenko and Kiselev, Sov. Phys. Semicond. 26, 827 (1992)] and readily conclude that ``the previous theory of the g factor in heterostructures is inadequate''. We show here that the entire discrepancy can be tracked down to an additional contribution missing in the incomplete elimination procedure of Pfeffer and Zawadzki. This mistake equally affects their ``exact'' and approximate results. When the overlooked terms stemming from the nondiagonal Zeeman interaction between light hole and spin-orbit-split valence states are taken into account in the effective electron dispersion, the results of the both approaches applied to the three-level kp model become identical.Comment: 5 pages, no figure

Inverse spin galvanic effect in the presence of impurity spin-orbit scattering: a diagrammatic approach

Spin-charge interconversion is currently the focus of intensive experimental and theoretical research both for its intrinsic interest and for its potential exploitation in the realization of new spintronic functionalities. Spin-orbit coupling is one of the key microscopic mechanisms to couple charge currents and spin polarizations. The Rashba spin-orbit coupling in a two-dimensional electron gas has been shown to give rise to the inverse spin galvanic effect, i.e. the generation of a non-equilibrium spin polarization by a charge current. Whereas the Rashba model may be applied to the interpretation of experimental results in many cases, in general in a given real physical system spin-orbit coupling also occurs due other mechanisms such as Dresselhaus bulk inversion asymmetry and scattering from impurities. In this work we consider the inverse spin galvanic effect in the presence of Rashba, Dresselhaus and impurity spin-orbit scattering. We find that the size and form of the inverse spin galvanic effect is greatly modified by the presence of the various sources of spin-orbit coupling. Indeed, spin-orbit coupling affects the spin relaxation time by adding the Elliott-Yafet mechanism to the Dyakonov-Perel and, furthermore, it changes the non-equilibrium value of the current-induced spin polarization by introducing a new spin generation torque. We use a diagrammatic Kubo formula approach to evaluate the spin polarization-charge current response function. We finally comment about the relevance of our results for the interpretation of experimental results.Comment: 14 pages, 1 figure, invited paper for a special issue of Condensed Matter (MDPI) on "Control and Enhancement of Quantum Coherence in Nanostructured Materials

Resonant Fibonacci Quantum Well Structures

We propose a resonant one-dimensional quasicrystal, namely, a multiple quantum well (MQW) structure satisfying the Fibonacci-chain rule with the golden ratio between the long and short inter-well distances. The resonant Bragg condition is generalized from the periodic to Fibonacci MQWs. A dispersion equation for exciton-polaritons is derived in the two-wave approximation, the effective allowed and forbidden bands are found. The reflection spectra from the proposed structures are calculated as a function of the well number and detuning from the Bragg condition.Comment: 5 pages, 3 figures, submitted to Phys. Rev.

Comparison of N. Atlantic heat storage estimates during the Argo period (1999–2010)

Ocean heat storage is an essential component of the climate system and there is considerable interest in its accurate evaluation. There are a number of heat storage products produced by many different groups. These products are derived from Argo as well as other platforms, for example XBT and CTD, in the last decade. Here we compare two heat storage estimates for the North Atlantic 0–2000 m from 10° to 70° N. One derived solely from Argo data whilst the other is derived from Argo and other platforms. It is found that there is a positive trend in heat storage over the period 1999–2010. This trend is influenced by a strong air–sea interaction event in 2009–2010, and this reduces the upward trend 1999–2008 identified previously. Both data sets are consistent with each other for the layer 0–1000 m on a timescale of beyond 1 yr. There are significant differences at sub-annual time scales and in the layer 1000–2000 m

Spin orientation of two-dimensional electron gas under intraband optical pumping

The theory of spin orientation of two-dimensional (2D) electron gas has been developed for intrasubband indirect optical transitions. The monopolar optical orientation of electrons in the conduction band is caused by the indirect scattering with virtual intermediate states in the valence band and allowance for selection rules for interband transitions. The considered mechanism of optical orientation is shown to be in an inherent relation with the special Elliot-Yafet mechanism of electron spin relaxation induced by virtual interband scattering.Comment: 3 pages, 2 figures, Symposium "Nanostructures: Physics and Technology", St.Petersburg, Russia, 200

Electron scattering in quantum wells subjected to an in-plane magnetic field

It is shown that the electron scattering by static defects, acoustic or optical phonons in quantum wells subjected to an in-plane magnetic field is asymmetric. The probability of scattering contains terms which are proportional to both the electron wave vector and the magnetic field components. The terms under study are caused by the lack of an inversion center in quantum wells due to structure or bulk inversion asymmetry although they are of pure diamagnetic origin. Such a magnetic field induced asymmetry of scattering can be responsible for a number of phenomena. In particular, the asymmetry of inelastic electron-phonon interaction leads to an electric current flow if only the electron gas is driven out of thermal equilibrium with the crystal lattice.Comment: 5 pages, 1 figur