Spin- and angle-resolved inverse photoemission setup with spin orientation independent from electron incidence angle

Abstract

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 k B T eff 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 Δ k F ≲ 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.

On the energy resolution of a GaAs-based electron source for spin-resolved inverse photoemission

“…However, if the Rashba parameter is very small, the spin effects may not be observed in IPES due to the constraints on the energy resolution, usually of hundreds of meV. A prototypical system for studying the Rashba splitting is the Shockley surface state of Au, studied below [14][15][16] and above the Fermi level [1,17], with a spin that is tangent to the concentric Fermi surface. We present in Fig.…”

“…In the LT, the binding energy of the state is more defined as follows from the FWHM. details on the surface resonance and spin-polarized bulk states have been discussed elsewhere [1,17]. The lifetime of the Shockley surface state is apparently smaller when approaching normal incidence due to the particular experimental constraints.…”

“…The spin-resolution is incorporated in the room temperature measurements on freshly-prepared samples by the near-infrared photoemission (~830 nm) from a negative electron affinity GaAs wafer, already detailed for isochromat IPES [1]. The net polarization of the photocathode is reported to be 0.30 0.03.…”

“…The exploration of unoccupied states with total spin control is now possible in inverse photoemission (IPES) by fully decoupling the spin polarization vector of the electron beam from its wavevector [1]. The decoupling of the polarization orientation of the electron beam from the wavevector allows exploring the unoccupied bands with the spin orientation more suitable to explore every state.…”

“…Yet, even when samples could stand relatively high currents, the electronelectron repulsion becomes important in low-energy and high-brightness beams, affecting not only the energy but also the momentum resolution [11,12]. The selected transfer energy in the electron optics has been chosen to reduce them [1]. Therefore, the effects of the spacecharge are observed as a decrease in the lifetime of the surface state while increasing the electron current at the target.…”