Search

We reply to the Comment by Donath et al. on our setup, which allows a total 3D control of the polarization direction of the electron beam in an inverse photoemission spectroscopy (IPES) experiment, a significant advance with respect to previous setups with partial polarization control. Donath et al. claim an incorrect operation of our setup after comparing their results, treated to enhance the spin asymmetry, with our spectra without the same treatment. They also equal spectra backgrounds instead of equaling peak intensities above the background. Thus, we compare our Cu(001) and Au(111) results with the literature. We reproduce previous results, including spin-up/spin-down spectral differences observed for Au and not observed for Cu. Also, spin-up/spin-down spectral differences appear at the expected reciprocal space regions. In the Comment, it is also stated that our tuning of the spin polarization misses the target because the spectra background changes when tuning the spin. We argue that the background change is irrelevant to IPES since the information is contained in peaks produced by primary electrons, those having conserved their energy in the inverse photoemission process. Second, our experiments agree with previous results from Donath et al. [Wissing et al., New J. Phys. 15, 105001 (2013)] and with a zero-order quantum-mechanical model of spins in vacuum. Deviations are explained by more realistic descriptions including the spin transmission through an interface. Consequently, the operation of our original setup is fully demonstrated. Our development corresponds to "the promising and rewarding angle-resolved IPES setup with the three-dimensional spin resolution," as indicated in the Comment, after our work. [ABSTRACT FROM AUTHOR]

Improving the efficiency of spin generation, injection, and detection remains a key challenge for semiconductor spintronics. Electrical injection and optical orientation are two methods of creating spin polarization in semiconductors, which traditionally require specially tailored p-n junctions, tunnel or Schottky barriers. Alternatively, we introduce here a novel concept for spin-polarized electron emission/injection combining the optocoupler principle based on vacuum spin-polarized light-emitting diode (spin VLED) making it possible to measure the free electron beam polarization injected into the III-V heterostructure with quantum wells (QWs) based on the detection of polarized cathodoluminescence (CL). To study the spin-dependent emission/injection, we developed spin VLEDs, which consist of a compact proximity-focused vacuum tube with a spin-polarized electron source (p-GaAs(Cs,O) or Na2KSb) and the spin detector (III-V heterostructure), both activated to a negative electron affinity (NEA) state. The coupling between the photon helicity and the spin angular momentum of the electrons in the photoemission and injection/detection processes is realized without using either magnetic material or a magnetic field. Spin-current detection efficiency in spin VLED is found to be 27% at room temperature. The created vacuum spin LED paves the way for optical generation and spin manipulation in the developing vacuum semiconductor spintronics. [ABSTRACT FROM AUTHOR]

A new spin- and angle-resolved inverse photoemission setup with a low-energy electron source is presented. The spin-polarized electron source, with a compact design, can decouple the spin polarization vector from the electron beam propagation vector, allowing one to explore any spin orientation at any wavevector in angle-resolved inverse photoemission. The beam polarization can be tuned to any preferred direction with a shielded electron optical system, preserving the parallel beam condition. We demonstrate the performances of the setup by measurements on Cu(001) and Au(111). We estimate the energy resolution of the overall system at room temperature to be ∼170 meV from kBTeff of a Cu(001) Fermi level, allowing a direct comparison to photoemission. The spin-resolved operation of the setup has been demonstrated by measuring the Rashba splitting of the Au(111) Shockley surface state. The effective polarization of the electron beam is P = 30% ± 3%, and the wavevector resolution is ΔkF ≲ 0.06 Å−1. Measurements on the Au(111) surface state demonstrate how the electron beam polarization direction can be tuned in the three spatial dimensions. The maximum of the spin asymmetry is reached when the electron beam polarization is aligned with the in-plane spin polarization of the Au(111) surface state. [ABSTRACT FROM AUTHOR]

A remarkably large spin signal is observed on nonmagnetic W(110) for a highly symmetric unoccupied state with no intrinsic spin polarization. The magnitude and, more importantly, the sign of this spin signal, measured by spin- and angle-resolved inverse photoemission for normal electron incidence, can be tuned in a user-defined manner by variation of the photon-detection angle and/or by rotating the spin-polarization direction of the incident electrons. Using calculations of the orbitally decomposed spectral densities, this effect is traced back to a mixing of different symmetries within the respective state. This explanation is underlined by the behavior of a second electronic state of pure symmetry, which does not show such a spin signal. In general, the spin signals of electronic states are not only influenced by their intrinsic spin polarization but also by the choice of symmetry-breaking experimental parameters in combination with the particular orbital characters of the states under investigation. The latter permits one to tune the spin signal in magnitude and sign. [ABSTRACT FROM AUTHOR]

The spin character of the splitting of the Shockley surface state on Au(111) is directly verified by measurements of the in-plane and out-of-plane spin polarizations in angle-resolved photoemission spectra. The two parabolic sub-bands that are momentum-shifted with respect to each other, reveal a distinct, opposite spin polarization that within the errors lies in the surface plane. The measured in-plane orientation of the spin vectors is consistent with the simple spin structure expected from a nearly-free-electron model, where the polarization axis is tangential to the Fermi surface of the surface state. [Copyright &y& Elsevier]

Photoelectron diffraction (PED) effects in magnetic solids are described within a one-electron non-relativistic model. The theory presented permits a straightforward calculation of spin-resolved PED patterns, whereby different spin arrangements in a magnetic solid may be considered. Both spin–orbit interaction and exchange interaction with the spin-polarized valence band have been taken into account in the description of the initial core state. The multiple scattering of the excited photoelectron wave is treated within a multiple-scattering cluster model. The theory may be applied to explain PED effects in magnetic solids in comparison to the nonmagnetic case. [Copyright &y& Elsevier]