Schematic depicting several designs of spin-ARPES spectrometers based on possible combinations of energy analyzers (HEA or TOF) and spin polarimeters (Mott or LEX). The combinations are represented by the overlapping circles and are labeled by the approximate efficiencies relative to the Mott-HEA combination (explained in text). The combinations on the left, top, and bottom have been previously developed. A spectrometer based on the combination on the right, marked by the green arrow, is reported here.
Drawing of the LEX polarimeter scattering and detection components. MCP detector with annular tube is shown in sectioned view. Electron path is shown by red dashed line. The inset shows two useful scattering geometries; the main figure shows polarimeter configured in the Planar geometry with the scattering plane coplanar with the plane.
Spin analyzing characteristics of a 50 monolayer Co/W(110) scattering target measured at normal incidence/reflection. (a) Spin-dependent reflectivity with incident beam 20% polarized along the target’s magnetization direction. Inset shows the spin-dependent band structure of bulk Co along the surface perpendicular direction (adapted from Ref. 74). (b) Corresponding . (c) Corresponding . The green horizontal bars cover the approximate range of scattering energy used for the polarimeter data in this paper.
Diagram of the spin-TOF spectrometer. LS1, LS2, LS3: Lens System 1, 2, and 3. BPF: bandpass filter. VA: variable aperture. ES: exit slit. Each electrode is wired as shown by 12 independent voltages. Deflectors are powered by 4 additional independent voltages (not shown). Electron paths for mode 1 (straight) and mode 2 (90° bend) are shown by the dashed red line.
(a) Schematic TOF spectrum, , which would result from the evenly distributed energy spectrum shown in the inset and with a flight length of 0.937 m. The corresponding energy resolution, , is shown by the right side axis assuming . Vertical black lines separate the spectrum into 328 ns wide segments. Flight energies corresponding to the flight times at these locations are marked. (b) With a 328 ns period between light pulses, the effective TOF spectrum is the sum of the segments in panel (a), shifted into the same time window and overlapping as shown. The vertical black line highlights relative intensities (resolutions) on the left (right) axis in the 220 ns time channel corresponding to the different flight energies labeled.
Photograph of the TOF lens system. Magnetic shielding and vacuum enclosures removed for view. EF: electrical feedthrough ports.
Schematic of data acquisition and instrument control electronics.
Typical “drift tube” photoemission spectrum taken with straight path (M1), acquired in with a total count rate of 135 kHz. The angular resolution in the free drift case, defined by the size of the detector and flight length, is ±0.4°. The upper panel is the raw time spectrum and the lower panel is converted to an energy axis. The inset shows a close up of the W 4f core levels. The splitting of the surface component illustrates a clean surface.
Photoemission spectra taken with the spin-integrating detector of the W Fermi edge showing total experimental energy resolution. (a) Spectrum taken along straight path of M1 with , retardation, and angular resolution ±0.6°. Although the Fermi edge is sharp and recognizable, the spectrum badly overlaps with itself, resulting in the confusing full spectrum shown in the inset. The box in the inset corresponds to the range expanded in the main panel. The peaks under the vertical arrows mark signal from the 4f core levels coming from higher order light of pulses one period after those causing the signal at . (b) Same spectrum taken with BPF in M2 with retardation and angular resolution ±0.4°. The energy resolution is similar to (a), but the spectrum is completely free of spectral overlap.
Spectra taken from Au(111) surface state. (a) Spin-integrated M1 data as a function of emission angle along . Spectra are vertically shifted for clarity. (b) Spin-resolved M2 data, taken at the angle corresponding to black spectrum in (a), with angular resolution ±0.9° and a total acquisition time of 3 h. Solid curves are fits to Gaussian peaks with a linear background and the Fermi function.
The flat and featureless portion of the Au/W(110) photoemission spectrum corresponding to binding energy . (a) The intensity measured with the scattering target magnetized “up” (red upward triangles) and “down” (blue downward triangles). The resulting asymmetry is shown in (b). As no polarization is expected, this shows an extremely low .
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