Very efficient spin polarization analysis (VESPA): new exchange scattering-based setup for spin-resolved ARPES at APE-NFFA beamline at Elettra

Abstract

Complete photoemission experiments, enabling measurement of the full quantum set of the photoelectron final state, are in high demand for studying materials and nanostructures whose properties are determined by strong electron and spin correlations. Here the implementation of the new spin polarimeter VESPA (Very Efficient Spin Polarization Analysis) at the APE-NFFA beamline at Elettra is reported, which is based on the exchange coupling between the photoelectron spin and a ferromagnetic surface in a reflectometry setup. The system was designed to be integrated with a dedicated ScientaOmicron DA30 electron energy analyzer allowing for two simultaneous reflectometry measurements, along perpendicular axes, that, after magnetization switching of the two targets, allow the three-dimensional vectorial reconstruction of the spin polarization to be performed while operating the DA30 in highresolution mode. VESPA represents the very first installation for spin-resolved ARPES (SPARPES) at the Elettra synchrotron in Trieste, and is being heavily exploited by SPARPES users since autumn 2015.

Spin-orbit effects at chiral surfaces

“…By using the Rashba parameter appropriate for Bi/Ag(111) and a momentum expectation value associated with the longitudinal spin polarization, an energy shift of 24 meV is obtained. Below 100 K, thermal fluctuations are an insignificant factor in randomizing electron spins with respect to the longitudinal direction and, because the total instrumental resolution of state-of-the-art spin-resolved photoemission experiments at synchrotrons is ∼70 meV [37] or better [38], this will allow for the polarization of the surface states to be resolved in the future.…”

Electronic properties of candidate type-II Weyl semimetal WTe 2 . A review perspective

“…In case of spin-resolved ARPES, in addition to the energy and momentum of the electrons, the spin of the electrons is also determined. The spin detector used in our measurement utilizes highly efficient VLEED based spin polarimeter [54]. The photoemitted electrons are channeled to a pre-oxidized magnetic target using electrostatic lenses.…”

“…The spin asymmetry is given by A = (I + − I − )/(I + + I − ), where I + and I − are reflected VLEED electronic counts corresponding to positive and negative target magnetizations, respectively. Once the spectra is compared with a known spin polarization material, the actual spin polarization of the unknown system can be determined [54]. The spin polarization is quantified as P = A/S eff , where S eff is the effective Sherman function, which depends on the detector and instrument setup, and determined by comparing polarization of a known system (e.g.…”

Electronic structure of the α-(BEDT-TTF)2I3 surface by photoelectron spectroscopy

“…Note that the cleavage occurs on the pa´bq plane between the loosely bonded BEDT-TTF and I 3 layers. The data were collected at the end station with a VG-DA30 Scienta hemispherical analyzer, that operates in deflection mode and provides high-resolution two-dimensional (2D) maping of the k-space (for more beamline specifications details see [22,23]). The total measured energy resolution is " 15 meV and the angular resolution is better than 0.2 0 .…”