Most novel phenomena discovered in modern condensed matter physics, such as high-temperature superconductivity, the Kondo effect, giant magnetoresistance, topological insulators, and the quantum anomalous Hall effect, are related to exchange or spin-orbital interactions, which are strongly influenced by the spin of electrons. However, the efficiency to detect electron spin using conventional angle-resolved photoelectron spectroscopy instrumentation is extremely low. Limited by such a low efficiency, researchers have to do the spin-resolved experiment with compromised resolution in both energy and momentum to achieve sufficient signal.
The efficiency of a spin polarimeters, so-called figure of merit, is 10-4 for traditional Mott-type detector. It would take much longer time (x104) to obtain a spin-resolved spectrum that has the same data statistics as the spin-integrated spectrum. It makes the spin resolved experiment a very difficult task in real experiment.
To overcome this challenge, and transform the state-of-art hemispherical energy analyzer for multi-channel detecting of spin, scientists from the Division of Condensed Matter Physics and Photon Science (DCPS) in ShanghaiTech University’s School of Physical Science and Technology (SPST) successfully realized a multichannel exchange scattering spin polarimeter, which can simultaneously detect the electron spins in a wide range of momentums. Being 5 × 105 times more efficiency than a classical Mott polarimeter, this new type of spin polarimeter enables the observation of detailed spin-polarized electronic structures with unprecedentedly high resolution. These scientists demonstrated the ability of this multi-channel spin polarimeter by measurements on bismuth (111), where the detailed momentum dependence of the spin splitting magnitude is quantitatively provided, showing a strong Rashba type splitting behavior in the surface scattered bulk states as well as the surface band.
This great improvement achieved in the efficiency of detecting the electron spins paves the way to study novel spin related phenomena with unprecedented accuracy.
The full credit of this research: Fuhao Ji, Tan Shi, Mao Ye, Weishi Wan, Zhen Liu, Jiajia Wang, Tao Xu, and Shan Qiao “Multichannel Exchange-Scattering Spin Polarimetry” Physical Review Letters 116(17), 177601 (2016).
(a) Schematic view of the multichannel spin polarimeter attached to a hemispherical energy analyzer; (b) Left, spin-integrated band dispersion of the Bi(111) surface; right, the scattering asymmetry for down- and up-spin; (c) and (d), Down- and up-spin band dispersion of both the surface Rashba state and bulk states of Bi(111).