Multichannel Exchange-Scattering Spin Polarimetry

Electron spin plays important roles in determining the physical and chemical properties of matter. However, measurements of electron spin are of poor quality, impeding the development of material sciences, because the spin polarimeter has a low efficiency. Here, we show an imaging-type exchange-scattering spin polarimeter with 6786 channels and an $8.5\times {10}^{-3}$ single channel efficiency. As a demonstration, the fine spin structure of the electronic states in bismuth (111) is investigated, for which strong Rashba-type spin splitting behavior is seen in both the bulk and surface states. This improvement paves the way to study novel spin related phenomena with unprecedented accuracy.

Figure 1

(a) Schematic view of the multichannel spin polarimeter attached to an energy analyzer. (b) An uncorrected electron intensity image on the 2D detector after performing a 6 eV VLEED reflection; the dark lines originate from a mesh set at the entrance of the spin polarimeter. (c),(d) The intensity distribution cut from (b) along the angle and energy directions; the instrumental FWHMs of the multichannel spin polarimeter are obtained by the method illustrated in (e).

Figure 2

(a) Spin-integrated [$I_{\text{total}}=(I_{+}+I_{-})/2$] band dispersion along the $\overline{M}-\overline{\mathrm{\Gamma }}-\overline{M}$ direction of the Bi(111) surface obtained using the multichannel spin polarimeter. (b) The scattering asymmetry obtained from two spectra taken under opposite target magnetization $A=(I_{+}-I_{-})/(I_{+}+I_{-})$. (c),(d) Schematic view of the crystal structure and surface Brillioun zone of Bi(111). (e),(f) The spin polarization and intensity EDC of the marked area in panel (a); the corresponding wave vector is $K_{\parallel }=0.1{\AA }^{-1}$. The strongest peak of the spin polarization at binding energy 0.8 eV is used to calibrate the effective Sherman function of the spin polarimeter. (g)–(i) The spin integrated and resolved spectrum of the Rashba state near the Fermi surface, corresponding to the upper marked area in (a). The spin up and down spectrum is obtained from $I_{\uparrow \downarrow }=(1\pm P)I_{\text{total}}/2$. Bands with opposite spin separate along $\pm K$, showing the reflection symmetry due to TRI.

Figure 3

(a),(b) Spin-down and spin-up band dispersion of both the surface Rashba state and bulk states. (c) The fitted Lorentzian peak positions in $k$ space of three bands marked in panels (a) and (b); the spin-up and spin-down band dispersions are put together. The uncertainty of the peak position is depicted by an error bar resulting from the energy resolution. (d) Momentum-dependent spin splitting magnitude obtained from (c); $E_{\mathrm{spm}}(n,k)=E_{\uparrow }(n,k)-E_{\downarrow }(n,k)$.