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

Chiara Bigi,Andrea Martin,Giorgio Rossi,Davide Benedetti,Ivana Vobornik,Jun Fujii,Damjan Krizmancic,Pranab K Das,Rudi Sergo,Federico Salvador,Giancarlo Panaccione

doi:10.1107/s1600577517006907

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 Scienta-Omicron 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 high-resolution 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.

Highlights

Probing the spin-resolved electron states of solids, surfaces and nanostructures gives direct access to phenomena like magnetism, proximity effects, spin–orbit interaction and related spin texture in low-dimensional systems (Bianchi et al, 2010; Jozwiak et al, 2011; Bahramy et al, 2012; Riley et al, 2014; Suzuki et al, 2014; Veenstra et al, 2014; Das et al, 2016; Mo et al, 2016)
Spin–orbit coupling manifests with the Rashba effect in two-dimensional systems (Hoesch et al, 2004; Yaji et al, 2010; Sakamoto et al, 2013; Takayama et al, 2014), Weyl semi-metals (Lv et al, 2015; Yang et al, 2015) and in the topological insulators where the surface states are characterized by a chiral spin texture and the spin is locked to the electron momenta (Hsieh et al, 2009; Xia et al, 2009; Pan et al, 2011; Zhu et al, 2014)
A state-of-the-art spin-resolved ARPES (SPARPES) spectrometer has been implemented under the NFFA-Trieste project and has been fully operational since the end of 2015 as a users facility at the beamline APE on the Elettra storage ring, accessible via the NFFA-Europe and NFFA-Trieste

Summary

Introduction

Probing the spin-resolved electron states of solids, surfaces and nanostructures gives direct access to phenomena like magnetism, proximity effects, spin–orbit interaction and related spin texture in low-dimensional systems (Bianchi et al, 2010; Jozwiak et al, 2011; Bahramy et al, 2012; Riley et al, 2014; Suzuki et al, 2014; Veenstra et al, 2014; Das et al, 2016; Mo et al, 2016). The VESPA spin in efficiency by a factor of 102 and rendering this polarimeter is made of two orthogonal VLEED reflectometers type of detection suitable for high-resolution ARPES receiving two energy- and momentum-selected electron $ 0.8 angular acceptance, corresponding to $ 0.38 A À1 at 30 eV photon energy) and the overall energy resolution is $ 100 meV (analyzer pass energy 20 eV) This allowed us to obtain the whole set of spin-polarized dispersion shown in Fig. 5(d) in $ 1 h.

Data management

Conclusion