Spin-Resolved ARPES
The electron is a tiny particle belongs to the class of subatomic particles called leptons, which are believed to be fundamental particles. Up to date, the electron's inner structure has yet be observed experimentally. Thus an electron, besides its mass, possesses only two intrinsic properties: charge and spin.
We know that the charge of the electron has been extensively used in our everyday electronics. Especially since the 1970s, conventional electronic microprocessors have operated by shuttling packets of electronic charge along ever-smaller semiconductor channels. Although this trend will continue for the next few years, current technology is beginning to approach fundamental limits when the quantum mechanics effects will prevent further scaling down of the electronic circuit.
The spin of the electron has attracted much interest recently, because it promises a wide variety of new devices that combine logic, storage, and sensor applications. Moreover, these "spintronic" devices might lead to quantum computers and quantum communication based on electronic solid-state devices, thus changing the perspective of information technology in the 21st century. It is thus important and urgent to develop an experimental tool to study the electron spin properties in materials as well as the regular electronic property.
Angle Resolved Photoemission spectroscopy (ARPES) has been established as one of the most important methods to study the electronic structure of molecules, solids and surfaces. It has widespread practical implications in various fields and has significantly contributed to the understanding of fundamental principles in solid state physics. If we can add the spin-resolving capability to ARPES, this powerful technique will become an ideal tool to study the magnetic materials and reveal their spin-related electronic structure.
To resolve the electrons spin, we use the Mott-scattering process, where high-energy electrons are scattered by heavy nuclei, causing the preferential scattering for spin up vs spin down electrons due to the spin-orbital coupling.
Since the Mott-scattering process involves accelerating the electrons to 104~105 eV and then having them scattered by a gold target, the photoelectrons will lose information about their original energy and momentum. Thus, prior to the spin-detection, we resolve the energy/momentum of the photoelectrons by a regular dispersive spherical analyzer. Then, photoelectrons of known momentum and energy enter the spin detector and get accelerated for spin detection. In this way, we can acquire the complete energy /momentum/spin information of the photoelectrons to determine the spin-resolved electronic structures in the sample. The figure below shows a schematic of our measurement scheme (left), and a sketch of our spectrometer (right).
With this new capability, we can now extend the ARPES study to many new fields, specially those related to the magnetism. Some such examples are shown below.
