Anisotropic transport in the two-dimensional electron gas in the presence of spin-orbit coupling

In a two-dimensional electron gas as realized by a semiconductor quantum well, the presence of spin-orbit coupling of both the Rashba and Dresselhaus type leads to anisotropic dispersion relations and Fermi contours. We study the effect of this anisotropy on the electrical conductivity in the presence of fixed impurity scatterers. The conductivity also shows in general an anisotropy which can be tuned by varying the Rashba coefficient. This effect provides a method of detecting and investigating spin-orbit coupling by measuring spin-unpolarized electrical currents in the diffusive regime. Our approach is based on an exact solution of the two-dimensional Boltzmann equation and provides also a natural framework for investigating other transport effects including the anomalous Hall effect.Comment: 10 pages, 1 figure included. Discussion of experimental impact enlarged; error in calculation of conductivity contribution corrected (cf. Eq. (A14)), no changes in qualitative results and physical consequence

Spin-filtering and charge- and spin-switching effects in a quantum wire with periodically attached stubs

Spin-dependent electron transport in a periodically stubbed quantum wire in the presence of Rashba spin-orbit interaction (SOI) is studied via the nonequilibrium Green's function method combined with the Landauer-Buttiker formalism. The coexistence of spin filtering, charge and spin switching are found in the considered system. The mechanism of these transport properties is revealed by analyzing the total charge density and spin-polarized density distributions in the stubbed quantum wire. Furthermore, periodic spin-density islands with high polarization are also found inside the stubs, owing to the interaction between the charge density islands and the Rashba SOI-induced effective magnetic field. The proposed nanostructure may be utilized to devise an all-electrical multifunctional spintronic device.Comment: 4 pages, 4 figure

Electric Birefringence in Solutions of High Molecular Weight Ribonucleic Acid

The electric birefringence of low ionic strength solutions of high molecular weight ribonucleic acids from various sources was studied. RNA preparations with a high helical content were found to have negative electric birefringence as a result of the segment anisotropy of the helical portions of the RNA molecule. For completely unfolded molecules of RNA, the electric birefringence is positive and results from the orientation of the macromolecular coil. In intermediate cases, the observed electric birefringence is the sum of negative and positive birefringence. The negative birefringence is caused by the segment orientation of helical sections, and the positive birefringence is caused by the orientation of the macromolecular coil as a whole. Different relaxation times for the positive and negative birefringence permit the pulsed electric birefringence method to analyze these separate phenomena

Competition between the Hydride Ligands of Two Types in Proton Transfer to [{κ3-P-CH3C(CH2CH2PPh2)3}RuH(η2-BH4)]

The interaction of the mixed hydrido–tetrahydridoborate ruthenium(II) complex [(Triphos)RuH(η2-BH4)] [1; Triphos = κ3-P-CH3C(CH2CH2PPh2)3] with alcohols of variable acidic strength [MeOH, FCH2CH2OH (MFE), CF3CH2OH (TFE), (CF3)2CHOH (HFIP), and (CF3)3COH (PFTB)] was the subject of a combined computational (DFT) and spectroscopic (VT FTIR, NMR) study. The experimental spectra suggests that RuH···HO bond formation precedes the protonation of 1, and H2 evolution leads to the loss of boron and the formation of the dimetallic [{(Triphos)RuH}2(µ,η2:η2-BH4)]+ cation. The experimentally determined basicity factor [Ej(RuH)] of the Ru-bound hydrido ligand of 1.43 is among the highest determined for ruthenium hydrides. Such high basicity leads to very easy proton transfer to the RuH ligand for strong alcohols (HFIP and PFTB). An alternative reaction pathway involving the migration of the bridging hydride (BHbr) to the ruthenium center is suggested for weaker proton donors (MeOH and TFE). © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Competition between the Hydride Ligands of Two Types in Proton Transfer to [{κ3-P-CH3C(CH2CH2PPh2)3}RuH(η2-BH4)]

The interaction of the mixed hydrido–tetrahydridoborate ruthenium(II) complex [(Triphos)RuH(η2-BH4)] [1; Triphos = κ3-P-CH3C(CH2CH2PPh2)3] with alcohols of variable acidic strength [MeOH, FCH2CH2OH (MFE), CF3CH2OH (TFE), (CF3)2CHOH (HFIP), and (CF3)3COH (PFTB)] was the subject of a combined computational (DFT) and spectroscopic (VT FTIR, NMR) study. The experimental spectra suggests that RuH···HO bond formation precedes the protonation of 1, and H2 evolution leads to the loss of boron and the formation of the dimetallic [{(Triphos)RuH}2(µ,η2:η2-BH4)]+ cation. The experimentally determined basicity factor [Ej(RuH)] of the Ru-bound hydrido ligand of 1.43 is among the highest determined for ruthenium hydrides. Such high basicity leads to very easy proton transfer to the RuH ligand for strong alcohols (HFIP and PFTB). An alternative reaction pathway involving the migration of the bridging hydride (BHbr) to the ruthenium center is suggested for weaker proton donors (MeOH and TFE). © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Search for scission neutrons using specific angular correlations in 235U fission induced by slow polarized neutrons

Abstract The experimentadl atac oncernings cission or prescissionn eutronsa rev ery contradictorythe relativep art of theseneutronisn the prompt fissionn eutrons variesf rom I to 35 owing to arbitiary assumptionsm adei n differenta nalysesT. o solvet his problem,w e haveu seda new aliernativem ethodt o searchfo r the scissionn eutrons.W eh avef oundt he left right asymmetryo f prompt fission neutro n P FN emissionc ausebdy sp wavei nterlerencein the entrancec hannelo f the reactiona ndt he P odd asymmetry of the PFN emissionc ausedb y parityn onconservatioant the exit channeol f thef issionp rocessB. olh effecis cannotr esidei n PFN evaporated by excited fission fragments.The scission or prescissionn eutronsa reresponsible for these effect

Binuclearopper(I) borohydrideomplexontaining bridging bis(diphenylphosphino) methane ligands: Polymorphic structuresf [(μ2-dppm)2Cu2(η2-BH4)2] dichloromethane solvate

Bis(diphenylphosphino)methane copper(I) tetrahydroborate wasynthesized by ligandsxchange in bis(triphenylphosphine) copper(I) tetrahydroborate, and characterized by XRD, FTIR, NMR spectroscopy. According to XRD the title compound has dimerictructure, [(μ2-dppm)2Cu2(η2-BH4)2], and crystallizes as CH2Cl2 solvate in two polymorphic forms (orthorhombic, 1, and monoclinic, 2) The details of molecular geometry and the crystal-packing pattern in polymorphs were studied. Theare Twisted Boat-Boat conformation of the core Cu2P4C2 cycle in 1 is found being more stable than Boat-Boat conformation in 2. © 2017 by the authors. Licensee MDPI, Basel, Switzerland

Synthesis, structural properties and reactivity of ruthenocene-based pincer Pd(ii) tetrahydroborate

Two novel ruthenocene-based pincer palladium tetrahydroborates were characterized by XRD, NMR and FTIR. The alcoholysis of Pd(ii) tetrahydroborate LPd(BH4) (L = κ3-[{2,5-(tBu2PCH2)2C5H2}Ru(C5H5)]) yields the dinuclear cationic Pd(ii) tetrahydroborate with the bridging BH4- ligand [(LPd)2(μ,η1,2:η1,2-BH4)]+. The bifurcate dihydrogen-bonded complexes are the active intermediates of the first proton transfer in the step-wise alcoholysis of LPd(BH4), yielding eventually [(LPd)2(μ,η1,2:η1,2-BH4)]+. According to the X-ray and DFT/M06 geometry analysis, the BH4- ligand in both palladium tetrahydroborates has a mixed coordination mode η1,2. The possibility of BH3-group abstraction from LPd(BH4) by an excess of organic base (THF, Py) with the formation of hydride LPdIIH is shown. This Pd(ii) hydride is a very reactive compound able to rapidly capture CO2 (ca. 15 min) converting into the formate complex LPdII(η1-OC(O)H). The hydrolysis of LPdH with subsequent CO2 insertion yields a hydrocarbonate complex LPdII(η1-OC(O)OH). The hydrocarbonate complex forms hydrogen-bonded dimers in the crystal due to hydrogen bonds between the OC(O)OH fragments. © 2019 The Royal Society of Chemistry

Binuclearopper(I) borohydrideomplexontaining bridging bis(diphenylphosphino) methane ligands: Polymorphic structuresf [(μ2-dppm)2Cu2(η2-BH4)2] dichloromethane solvate

Bis(diphenylphosphino)methane copper(I) tetrahydroborate wasynthesized by ligandsxchange in bis(triphenylphosphine) copper(I) tetrahydroborate, and characterized by XRD, FTIR, NMR spectroscopy. According to XRD the title compound has dimerictructure, [(μ2-dppm)2Cu2(η2-BH4)2], and crystallizes as CH2Cl2 solvate in two polymorphic forms (orthorhombic, 1, and monoclinic, 2) The details of molecular geometry and the crystal-packing pattern in polymorphs were studied. Theare Twisted Boat-Boat conformation of the core Cu2P4C2 cycle in 1 is found being more stable than Boat-Boat conformation in 2. © 2017 by the authors. Licensee MDPI, Basel, Switzerland