Generation of spin-polarized hot electrons at topological insulators surfaces by scattering from collective charge excitations

Topological insulators (TIs) are materials which exhibit topologically protected electronic surface states, acting as mass-less Dirac fermions. Beside their fascinating fundamental physics, TIs are also promising candidates for future spintronic devices. In this regard, generation of spin-polarized currents in TIs is the first and most important step towards their application in spin-based devices. Here we demonstrate that when electrons are scattered from the surface of bismuth selenide, a prototype TI, not only the elastic channel but also the inelastic channel is strongly spin dependent. In particular collective charge excitations (plasmons) excited at such surfaces show a large spin-dependent electron scattering. Electrons scattered by these excitations exhibit a high spin asymmetry, as high as 40%. The observed effect opens up new possibilities to generate spin-polarized currents at the surface of TIs or utilize the collective charge excitations to analyze the electrons’ spin. The results are also important to understand the spin polarization of the photo-excited electrons excited at TIs surfaces. Moreover, our finding will inspire new ideas for using these plasmonic excitations in the field of spin-plasmonics.

High precision neutron inelastic cross sections on 16O

This work reports partial results of a (n, nγ) measurement on 16O. The γ rays of interest from the inelastic channel were detected using the Gamma Array for Inelastic Neutron Scattering (GAINS) spectrometer at the Geel Electron Linear Accelerator (GELINA) neutron source. A very thick (32.30(4) mm) SiO2 target was used. The main goal was to determine the angle-integrated γ-production cross section for the most important transitions. In this work we report the results for the main 16O transition and we emphasize a consistency check aiming to ensure data reliability. Our results are compared with theoretical calculations performed using the TALYS 1.8 code and with previously reported experimental data.

PROTON INELASTIC DIFFRACTION BY A BLACK NUCLEUS AND THE SIZE OF EXCITED NUCLEI

We systematically derive a length scale characterizing the size of a low-lying, β stable nucleus from empirical data for the diffraction peak angle in the proton inelastic differential cross-section of incident energy of ~ 1 GeV. In doing so, we assume that the target nucleus in the ground state is a completely absorptive "black" sphere of radius a. The cross-section πa2, where a is determined in such a way as to reproduce the empirical proton diffraction peak angle in the elastic channel, is known to agree with empirical total reaction cross-sections for incident protons to within error bars. By comparing the inelastic diffraction patterns obtained in the Fraunhofer approximation with the experimental ones, one can likewise derive the black sphere radius al for the excited state with spin l. We find that for 12 C , 58, 60, 62, 64 Ni , and 208 Pb , the value of al obtained from the inelastic channel is generally larger than the value of a from the elastic channel and tends to increase with the excitation energy. This increase is remarkable for the Hoyle state. Finally, we discuss the relation between al and the size of excited nuclei.

A Modified Thermal Boundary Resistance Model for FCC Structures

A modified lattice-dynamical model is proposed to calculate the thermal boundary resistance at the interface between two fcc lattices. The nonequilibrium molecular dynamics (MD) simulation is employed to verify the theoretical calculations. In our physical model, solid crystal argon is set at the left side and the right side structure properties are tunable by setting the atomic mass and the interactive energy strength among atoms with different values. In the case of mass mismatch, the predictions of the lattice-dynamical (LD) model agree well at low temperature while the calculations of the diffuse mismatch model (DMM) based on the detailed phonon dispersion agree well at high temperature with the MD simulations. The modified LD model, considering a partially specular and partially diffuse phonon scattering, can explain the simulations reasonably in the whole temperature rage. The good agreement between the theoretical calculations and the simulations may be attributed to that phonon scattering mechanisms are dominated by elastic scattering at the perfect interfaces. In the case of interactive energy strength mismatch, the simulations are under the predictions of both the theoretical models, which may be attributed to the fact that this mismatch can bring about an outstanding contribution to opening up an inelastic channel for heat transfer at the interfaces.

Charge Symmetry Breaking in Neutron-Proton Scattering above Pion Production Threshold

We examine the effect of the coupled N.6. inelastic channel on charge symmetry breaking in the np system. Our calculation includes the effects of mass splitting for the nucleon and delta multiplets in the channel coupling potentials. The results suggest that such effects become increasingly important at about 500 MeV laboratory energy.