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A study of graphene on metal nanotextured surfaces for ultra-broadband light trapping, blackbody absorbers, and thermal imaging.

Exciton-exciton recombination in isolated semiconducting single-walled carbon nanotubes was studied using femtosecond transient absorption. Under sufficient excitation to saturate the optical absorption, we observed an abrupt transition between reaction- and diffusion-limited kinetics, arising from reactions between incoherent localized excitons with a finite probability of ~0.2 per encounter. This represents the first experimental observation of a crossover between classical and critical kinetics in a 1D coalescing random walk, which is a paradigm for the study of nonequilibrium systems.

We have used time-resolved spectroscopy to measure the relaxation of spin polarizations in the narrow gap semiconductor material n-InAs as a function of temperature, doping, and pump wavelength. The results are consistent with the D'Yakonov-Perel mechanism for temperatures between 77 and 300 K. However, the data suggest that electron-electron scattering should be taken into account in determining the dependence of the spin lifetime on the carrier concentration in the range 5.2ϫ 10 16 − 8.8ϫ 10 17 cm −3 . For a sample with doping of 1.22ϫ 10 17 cm −3 the spin lifetime was 24 ps at room temperature. By applying a magnetic field in the sample plane we also observed coherent precession of the spins in the time domain, with a g factor g * = −13, also at room temperature.

We report Larmor precession in bulk InSb observed in the time domain from 77 to 300 K. The optically oriented polarization precesses coherently even at 300 K. The inferred Zeeman spin splitting is strongly nonparabolic, and the electron g factor ͑g * ͒ is in good agreement with k · p theory ͑provided we take only the dilational contribution to the change in energy gap with temperature͒. We also show here that correct application of the 14-band k · p model agrees with apparently anomalous trends previously reported for GaAs and confirm that the most widely quoted formula for g * in GaAs is incomplete. DOI: 10.1103/PhysRevB.77.033204 PACS number͑s͒: 72.25.Fe, 71.70.Ej, 72.25.Rb, 78.47.-p InSb is an interesting semiconductor from the point of view of tests of semiconductor band structure calculations because the heavy constituent atoms produce large relativistic effects such as spin-orbit coupling ͑responsible for the large, negative gyromagnetic ratio͒. InSb is also a candidate material for room-temperature spintronic devices such as the Das-Datta spin transistor, which relies on a coherent spin population manipulated by the Rashba effect, and thus, detailed investigation of the spin-electronic structure in this material at room temperature is of high topical interest. In the present work, we report the experimental measurement of the g factor in InSb at temperatures up to 300 K and the theoretical evaluation of g * ͑T͒ for both InSb and GaAs.Although it has been claimed that measurements of the g factor of GaAs at 300 K are inconsistent with k · p perturbation theory, 1-4 this theory has been successfully used for decades to calculate the band structure in bulk semiconductors and heterostructures, [5][6][7][8][9][10][11][12][13][14] and, in particular, the conduction band effective mass and g factor. We show here that provided we include only the dilational change of the energy gap with temperature, 8,13 we obtain reasonable agreement between experiment and theory for the high-temperature g factor in both InSb and GaAs, and there is no anomaly. The higher band k · p parameters have only a very small effect on the electron g factor for InSb, but they are very important for GaAs; in particular, we confirm that it is essential to include the effects of the interband spin-orbit coupling parameter, which was previously ignored in the Hermann and Weisbuch formula for g * ͑Ref. 9͒ used in Refs. 1 and 2.In an externally applied magnetic field, the electron energy is given bymeasured from the ⌫ 6 conduction band edge, where B is the Bohr magneton, the quantum numbers Ϯ refer to the spin, n to the Landau level index, and k B to the component of momentum parallel to the magnetic field B. In the parabolic approximation, the effective mass and g factor, m * and g * , are constants and independent of n, k B , and B. The nonparabolicity of GaAs is usually taken to be small because the dependence of the effective mass on electron energy is small. 7 However, the g value, although small in magnitude, is significantly nonparabo...