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Utilizing time-resolved Kerr rotation techniques, we have investigated the spin dynamics of a high mobility, low density two dimensional electron gas in a GaAs/Al 0.35 Ga 0.65 As heterostructure in dependence on temperature from 1.5 K to 30 K. It is found that the spin relaxation/dephasing time under a magnetic field of 0.5 T exhibits a maximum of 3.12 ns around 14 K, superimposed on an increasing background with rising temperature. The appearance of the maximum is ascribed to that at the temperature where the crossover from the degenerate to the nondegenerate regime takes place, electron-electron Coulomb scattering becomes strongest, and thus inhomogeneous precession broadening due to D'yakonov-Perel' (DP) mechanism becomes weakest. These results agree with the recent theoretical predictions [Zhou et al., PRB 75, 045305 (2007)], verifying the importance of electron-electron Coulomb scattering to electron spin relaxation/dephasing. PACS numbers: 72.25.Rb, 71.70.Ej, 78.47.jc In recent years, spin dynamics in semiconductors has attracted considerable attention because of its potential application in the spin-based devices. 1 The operation of these devices requires spin lifetime long enough to achieve storage, transport and processing of information. Therefore, a comprehensive understanding of spin relaxation mechanism is a key factor for the realization of these devices. It is generally accepted that the D'yakonov-Perel' (DP) mechanism is the leading spin relaxation/dephasing (R/D) mechanism in n-type zincblende semiconductors. 2 This is caused by an wavevector kdependent effective magnetic field Ω(k) from the bulk inversion asymmetry, 3 i.e., the Dresselhaus term, and/or the structure inversion asymmetry, 4 i.e., the Rashba term. The spin relaxation rate can be determined by τ −1 = Ω(k) 2 τ P (k), where τ P (k) is the momentum relaxation time. 5 As the electronelectron Coulomb scattering does not contribute to the momentum relaxation time τ p , it has long been widely believed that the electron-electron Coulomb scattering is irrelevant in the spin relaxation. 5,6,7,8,9,10,11 However, it was first pointed out by Wu and Ning 12 that in the presence of inhomogeneous broadening, any scattering, including the spin conserving electron-electron Coulomb scattering, can cause an irreversible spin relaxation and dephasing. This inhomogeneous broadening can be the energy-dependent g-factor, 12 the DP term, 13,14 and even the k-dependent spin diffusion along a spacial gradient. 15 In n-type GaAs quantum well, the importance of the electron-electron scattering to the spin relaxation was proved by Glazov and Ivchenko 16 by using perturbation theory and Weng and Wu 14 from a fully microscopic many-body approach. In a temperature-dependent experimental study of the spin relaxation in n-type (001) quantum wells, Harleyet al. indirectly verified the effects of the electron-electron scattering on spin relaxation. 17,18 Nevertheless, the importance of the Coulomb scattering to the spin relaxation/dephasing (R/D)has not yet been ...

Vortex dynamics in a multiband anisotropic superconductor, such as the Fe based superconductors, is interesting and potentially important for applications. In this study we examine flux-creep data for fields along the second magnetization peak observed in M(H) curves of BaFe 1.9 Ni 0.1 As 2 for H c-axis, H ab-planes and H forming a 45 • angle with ab-planes. We find that the M-H loops taken from the different field directions can be collapsed onto a single universal curve at all temperatures with a simple scaling factor equivalent to the superconducting anisotropy, showing that the vortex pinning is not only isotropic and three-dimensional but most likely related to point-like defects. The resulting critical currents, however, taken from the Bean model appear to show enhanced low field pinning for H c. The features in the vortex dynamics also differ in different field orientations and show no direct correlation with the second magnetization peak H p as is the case with a direct crossover in pinning regimes. Isofield plots of the scaled activation energy obtained from flux-creep data are found to be a smooth function of temperature as the H p (T) line is crossed, consistent with a single type of pinning regime operating at this field, independent of field orientation. The functional form of the H p (T) lines in the resulting phase diagrams also support this view.

Using ferroelectric 0.67Pb͑Mg 1/3 Nb 2/3 ͒O 3 -0.33PbTiO 3 single crystals as substrates, we studied the effects of the ferroelectric poling and the converse piezoelectric effect on the strain state, resistance, insulator-to-metal transition temperature ͑T C ͒, and magnetoresistance ͑MR͒ of La 0.7 Ba 0.3 MnO 3 ͑LBMO͒ thin films. In situ x-ray diffraction measurements indicate that the ferroelectric poling ͑or the converse piezoelectric effect͒ induces a substantial reduction in the in-plane tensile strain in the LBMO film, giving rise to a decrease in the resistance and an increase in T C . The relative changes of the resistance and T C are proportional to the induced reduction in the in-plane tensile strain ͑␦ xx ͒ in the film. The reduction in the in-plane tensile strain leads to opposite effects on MR below and above T C , namely, MR is reduced for T Ͻ T C while MR is enhanced for T Ͼ T C . We discuss these strain effects within the framework of the Jahn-Teller ͑JT͒ electron-lattice coupling and phase separation scenario that are relevant to the induced strain. Similar studies on CaMnO 3 thin films, for which there is no JT distortion of MnO 6 octahedra, show that the resistance of the films also decreases when the tensile strain is reduced, indicating that the resistance change arising from the reduction in Mn-O bond length dominates over that arising from the reduction in Mn-O-Mn bond angle.

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The suitability for use in pyroelectric detectors of single-crystalline doped and undoped lead indium niobate-lead magnesium niobate-lead titanate was tested and compared with high-quality Mn-doped lead magnesium niobate-lead titanate and standard lithium tantalate. Pyroelectric and dielectric measurements confirmed an increased processing and operating temperature range because of the higher phase transitions of lead indium niobate-lead magnesium niobate-lead titanate. Pyroelectric coefficients of 705 to 770 μC/m(2)K were obtained with doped and undoped lead indium niobate-lead magnesium niobate-lead titanate, which are about 70% to 80% of the pyroelectric coefficient of lead magnesium niobate-lead titanate but 4 times higher than standard lithium tantalate. Manganese doping has been proved as a solution to decrease the dielectric loss of lead magnesium niobate-lead titanate and it also works well for lead indium niobate-lead magnesium niobate-lead titanate. An outstanding specific detectivity D* of about 1.1 · 10(9) cm·Hz(1/2)/W was achieved at a frequency of 2 Hz for Mn-doped lead magnesium niobate-based detectors.

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