Spin and charge optical conductivities in spin-orbit coupled systems

We study the frequency dependent spin- and charge- conductivity tensors of a two-dimensional electron gas (2DEG) with Rashba and Dresselhaus spin-orbit interaction. We show that the angular anisotropy of the spin-splitting energy induced by the interplay between the Rashba and Dresselhaus couplings gives rise to a characteristic spectral behavior of the spin and charge response which is significantly different from that of pure Rashba or Dresselhaus case. Such new spectral structures open the possibility for control of the optical response by applying an external bias and/or by adjusting the light frequency. In addition, it is shown that the relative strength of the spin-orbit coupling parameters can be obtained through optical probing.Comment: 13 pages, 4 figures. Revised versio

Room temperature electron spin coherence in telecom-wavelength quaternary quantum wells

Time-resolved Kerr rotation spectroscopy is used to monitor the room temperature electron spin dynamics of optical telecommunication wavelength AlInGaAs multiple quantum wells lattice-matched to InP. We found that electron spin coherence times and effective g-factors vary as a function of aluminum concentration. The measured electron spin coherence times of these multiple quantum wells, with wavelengths ranging from 1.26 microns to 1.53 microns, reach approximately 100 ps at room temperature, and the measured electron effective g-factors are in the range from -2.3 to -1.1.Comment: 4 pages, 4 figure

Fluktuasi Curah Hujan Dan Komunitas Serangga Di Hutan Tropis Taman Nasional Gunung Halimun*[fluctuation of Rainfall and Insect Community in a Tropical Forest, Gunung Halimun National Park]

Study on fluctuation of rainfall and insect community was conducted in a tropical forest, Gunung Halimun National Park. Ten years rainfall data was available to discuss their fluctuations. Rainfall was relatively non-seasonal with high number of almost entire monthly rainfalls.Although fluctuation of rainfall in GHNP did not show clear seasonal trend, however appearance of less rainfall showed from June to September. There were several slight fluctuations in the number of rainfalls from a month to another and some time showed major and minor peaks. Monthly dry months had never reached 0 mm. In ordinary years, only one-month drought occurred in July 1991 (90 mm) and December 2000 (8 mm). Strong drought occurred only during El Nino of 1994 and 1997, which have 3 to 4 dry months. Fluctuation of insect community was studied from March 2000 up to February 2001. Two insect collection methods were applied by setting up light traps and pitfall traps. Total individual of each order of insect counted monthly and to be compared one to another. Changing the number of monthly individual of each order was interpreted to the number of monthly rainfall in order to analyze the relation of changing of the number of rainfall and the individual of each order of the insect collected. Fluctuation of the number of monthly rainfall was synchronous to the number of insect community collected by light traps (night flying insect) but tend to opposite to the number of insect collected by pitfall traps (ground insect)

Persepsi Dan Partisipasi Masyarakat Pasangan Usia Muda Terhadap Program Keluarga Berencana Di Desa Giripanggung

Kabupaten Gunung Kidul merupakan salah satu kabupaten di DI. Yogyakarta yang memiliki angka perkawinan usia muda yang cukup tinggi. Penelitian persepsi dan partisipasi masyarakat pasangan usia muda dalam program keluarga berencana di Desa Giripanggung Kecamatan Tepus Kabupaten Gunung Kidul bertujuan untuk: (1) Mengetahui persepsi pasangan usia muda terhadap pelaksanaan program Keluarga Berencana; (2) Mengetahui bentuk praktek partisipasi pasangan usia muda terhadap pelaksanaan program Keluarga Berencana. Teknik analisis data yang digunakan ada beberapa cara antara lain: (1) Tahap pengumpulan data, (2) Tahap pengolahan data, (3) Tahap analisis data, (4)Tahap penarikan kesimpulan. Pelaksanakan program KB di Desa Giripanggung sudah berjalan cukup baik namun masih saja ada hambatan dalam pelaksanakannya. Hal ini dibuktikan 2 dengan hasil dari penelitian ini adalah karakteristik pasangan usia muda di Desa Giripanggung memiliki kualitas SDM yang rendah. Praktek partisipasi masyarakat pasangan usia muda terhadap pelaksanakan KB mengalami penyimpangan karena tidak adanya pengawasan yang baik

Gate control of the spin mobility through the modification of the spin-orbit interaction in two-dimensional systems

Spin drag measurements were performed in a two-dimensional electron system set close to the crossed spin helix regime and coupled by strong intersubband scattering. In a sample with uncommon combination of long spin lifetime and high charge mobility, the drift transport allows us to determine the spin-orbit field and the spin mobility anisotropies. We used a random walk model to describe the system dynamics and found excellent agreement for the Rashba and Dresselhaus couplings. The proposed two-subband system displays a large tuning lever arm for the Rashba constant with gate voltage, which provides a new path towards a spin transistor. Furthermore, the data shows large spin mobility controlled by the spin-orbit constants setting the field along the direction perpendicular to the drift velocity. This work directly reveals the resistance experienced in the transport of a spin-polarized packet as a function of the strength of anisotropic spin-orbit fields.Comment: 6 pages, 4 figure

Small-angle impurity scattering and the spin Hall conductivity in 2D systems

An arbitrarily small concentration of impurities can affect the spin Hall conductivity in a two-dimensional semiconductor system. We develop a Boltzmann-like equation that can be used for impurity scattering with arbitrary angular dependence, and for arbitrary angular dependence of the spin-orbit field b(k) around the Fermi surface. For a model applicable to a 2D hole system in GaAs, if the impurity scattering is not isotropic, we find that the spin Hall conductivity depends on the derivative of b with respect to the energy and on deviations from a parabolic band structure, as well as on the angular dependence of the scattering. In principle, the resulting spin Hall conductivity can be larger or smaller than the ``intrinsic value'', and can have opposite sign. In the limit of small angle scattering, in a model appropriate for small hole concentrations, where the band is parabolic and b ~ k^3, the spin Hall conductivity has opposite sign from the intrinsic value, and has larger magnitude. Our analysis assumes that the spin-orbit splitting $b$ and the transport scattering rate tau^{-1} are both small compared to the Fermi energy, but the method is valid for for arbitrary value of b*tau.Comment: Errors corrected, references adde

Spin Hall effect in clean two dimensional electron gases with Rashba spin-orbit coupling

We study the spin polarization induced by a current flow in clean two dimensional electron gases with Rashba spin-orbit coupling. This geometric effect originates from special properties of the electron's scattering at the edges of the sample. In wide samples, the spin polarization has it largest value at low energies (close to the bottom of the band) and goes to zero at higher energies. In this case, the spin polarization is dominated by the presence of evanescent modes which have an explicit spin component outside the plane. In quantum wires, on the other hand, the spin polarization is dominated by interference effects induced by multiple scattering at the edges. Here, the spin polarization is quite sensitive to the value of the Fermi energy, especially close to the point where a new channel opens up. We analyzed different geometries and found that the spin polarization can be strongly enhanced.Comment: 10 pages, 13 figures, high quality figures available upon reques

Screening for coping style increases the power of gene expression studies

Background: Individuals of many vertebrate species show different stress coping styles and these have a striking influence on how gene expression shifts in response to a variety of challenges. Principal Findings: This is clearly illustrated by a study in which common carp displaying behavioural predictors of different coping styles (characterised by a proactive, adrenaline-based or a reactive, cortisol-based response) were subjected to inflammatory challenge and specific gene transcripts measured in individual brains. Proactive and reactive fish differed in baseline gene expression and also showed diametrically opposite responses to the challenge for 80% of the genes investigated. Significance: Incorporating coping style as an explanatory variable can account for some the unexplained variation that is common in gene expression studies, can uncover important effects that would otherwise have passed unnoticed and greatly enhances the interpretive value of gene expression data