Search

In spintronics, the two main approaches to actively control the electrons' spin involve static magnetic or electric fields. An alternative avenue relies on the use of optical fields to generate spin currents, which can bolster spin-device performance, allowing for faster and more efficient logic. To date, research has mainly focused on the optical injection of spin currents through the photogalvanic effect, and little is known about the direct optical control of the intrinsic spin-splitting. To explore the optical manipulation of a material's spin properties, we consider the Rashba effect. Using time- and angle-resolved photoemission spectroscopy (TR-ARPES), we demonstrate that an optical excitation can tune the Rashba-induced spin splitting of a two-dimensional electron gas at the surface of Bi

In spintronic devices, the two main approaches to actively control the electrons' spin degree of freedom involve either static magnetic or electric fields. An alternative avenue relies on the application of optical fields to generate spin currents, which promises to bolster spin-device performance allowing for significantly faster and more efficient spin logic. To date, research has mainly focused on the optical injection of spin currents through the photogalvanic effect, and little is known about the direct optical control of the intrinsic spin splitting. Here, to explore the all-optical manipulation of a material's spin properties, we consider the Rashba effect at a semiconductor interface. The Rashba effect has long been a staple in the field of spintronics owing to its superior tunability, which allows the observation of fully spin-dependent phenomena, such as the spin-Hall effect, spin-charge conversion, and spin-torque in semiconductor devices. In this work, by means of time and angle-resolved photoemission spectroscopy (TR-ARPES), we demonstrate that an ultrafast optical excitation can be used to manipulate the Rashba-induced spin splitting of a two-dimensional electron gas (2DEG) engineered at the surface of the topological insulator Bi$_{2}$Se$_{3}$. We establish that light-induced photovoltage and charge carrier redistribution -- which in concert modulate the spin-orbit coupling strength on a sub-picosecond timescale -- can offer an unprecedented platform for achieving all optically-driven THz spin logic devices.

Monte-Carlo (MC) methods, based on random updates and the trial-and-error principle, are well suited to retrieve particle size distributions from small-angle scattering patterns of dilute solutions of scatterers. The size sensitivity of size determination methods in relation to the range of scattering vectors covered by the data is discussed. Improvements are presented to existing MC methods in which the particle shape is assumed to be known. A discussion of the problems with the ambiguous convergence criteria of the MC methods are given and a convergence criterion is proposed, which also allows the determination of uncertainties on the determined size distributions., Accepted author manuscript, 7 pages, 7 figures

R,2'S)-l'-Oxo-2,2'-spirobi(indan)-l-yl (1 S)-4, 7,7-trimethyl- 3 -oxo-2-oxabicyclo )hept- (1972). A stereoselective reduction of one of the carbonyl groups in the diketone was performed with lithium tri-tert-butoxylaluminium hydride. The resulting alcohol group in the racemic trans-hydroxy ketone was transformed into an ester by acylation with (-)-to-camphanic acid chloride conserving the geometry of the reduced carbon. The two diaster- eomeric esters formed, (1) and (2), were separated by fractional crystallization. (1) had lower solubility in acetone than (2) and was isolated as nice pure crys- tals in the first fractions. (2), with a lower melting point than (1), was more difficult to isolate, and had to be recrystallized several times to obtain a single crystal useful for X-ray analysis. Equidimensional single-crystal fragments of maxi- mum dimensions less than 0.5 mm were used for the crystallographic examinations. The space groups of both crystals were determined from precession photographs to be monoclinic with only systematic absences 0k0 for k odd indicating P21. The lattice constants of both compounds were refined from approximately 25 centred reflections in the range 20 30-(/) were used for structure determination and refinements. It was observed that intensities drop more quickly with sin0/a for (2) than for (1), and so for (2) data were collected for 20 _ 3o-(1). The intensities were corrected for Lorentz and polarization effects. /z(1) = 0.83 cm-i and /~(2) = 0.81 cm -~, thus no absorption corrections were applied. Positions of all C and O atoms in the structures were found by direct methods (Sheldrick, 1990). H-atom positions were found from difference Fourier maps. The structures were refined by full- matrix least-squares techniques using anisotropic thermal parameters for the non-H atoms and iso