A high-efficiency spin-resolved photoemission spectrometer combining time-of-flight spectroscopy with exchange-scattering polarimetry

Abstract

We describe a spin-resolved electron spectrometer capable of uniquely efficient and high energy resolution measurements. Spin analysis is obtained through polarimetry based on low-energy exchange scattering from a ferromagnetic thin-film target. This approach can achieve a similar analyzing power (Sherman function) as state-of-the-art Mott scattering polarimeters, but with as much as 100 times improved efficiency due to increased reflectivity. Performance is further enhanced by integrating the polarimeter into a time-of-flight (TOF) based energy analysis scheme with a precise and flexible electrostatic lens system. The parallel acquisition of a range of electron kinetic energies afforded by the TOF approach results in an order of magnitude (or more) increase in efficiency compared to hemispherical analyzers. The lens system additionally features a 90 degrees bandpass filter, which by removing unwanted parts of the photoelectron distribution allows the TOF technique to be performed at low electron drift energy and high energy resolution within a wide range of experimental parameters. The spectrometer is ideally suited for high-resolution spin- and angle-resolved photoemission spectroscopy (spin-ARPES), and initial results are shown. The TOF approach makes the spectrometer especially ideal for time-resolved spin-ARPES experiments.

Widespread spin polarization effects in photoemission from topological insulators

“…Figure 2 shows data taken with the spin-resolved spectrometer. Panel (a) shows a stack of spin-integrated energy distribution curves (EDCs) taken along ΓM (the k x axis as defined in the present geometry) in the rapidacquisition mode of the spectrometer [25]. Several features are visible near the Fermi level, including the surface state and bulk valence and conduction band peaks.…”

“…Ref. 25 and references therein). It shows a clear peak near E F , again in line with the expected polarization of the UDC, and a smooth positive feature through the BVB at E −0.5 eV.…”

“…Using a recently developed high-efficiency and highresolution spin-ARPES spectrometer [25], we have extensively studied the spin-polarized photoemission spectrum of the 3D topological insulator Bi 2 Se 3 at both cryogenic Photoelectrons are collected along the vector ke that is a fixed 45…”

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

“…Other approaches have therefore been developed, which exploit the exchange interaction between low-energy photoemitted electrons and magnetically ordered target surfaces in LEED-like reflectometry geometries, leading to the increase in efficiency by a factor of 10 2 and rendering therefore this type of detection suitable for high-resolution ARPES (Kutnyakhov et al, 2013;Jozwiak et al, 2010;Bertacco et al, 2002). Here we report on the design, the implementation and the operational parameters of an optimized three-dimensional vectorial spin polarimeter that operates in the very low energy electron diffraction (VLEED) regime.…”

New Developments in Spin-Dependent Photoemission

“…The third line of evolution aimed * This paper was presented at the 11th International Symposium on Atomic Level Characterizations for New Materials and Devices '17, Aqua Kauai Beach Resort, Kauai, Hawaii, USA, December [3][4][5][6][7][8]2017. † Corresponding author: c.m.schneider@fz-juelich.de at improving the efficiency of explicit spin polarization detection by moving from standard single-channel high energy Mott detectors [11][12][13] to low-energy single-channel [14][15][16] and multi-channel polarimeters [17][18][19]. A more concise compilation of the various spin-resolving photoelectron spectroscopy concepts is given in a recent review by Okuda [20].…”