Angle-Resolved Photoemission Spectroscopy
The ARPES technique has seen continuous development with time. The distinct difference of the ARPES technique in this book is a high resolution spectroscopy system combined with a narrow band vacuum ultra-violet (VUV) laser, giving a total energy resoluti
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Angle-Resolved Photoemission Spectroscopy
2.1 Introduction The macroscopic properties of solid materials are governed by their microscopic electronic structures, so it’s important to study its electronic structure in order to understand, control or make use of the novel physics in various advanced materials. Electronic states in materials are reflected by the electron energy (E), momentum (k), and spin (s). ARPES is the sole technique that could probe all these physical quantities in solid materials, and this highly sophisticated experimental tool has played and irreplaceable role in the study of superconducting energy gap, pseudogap and many-body physics in cuprate high-temperature superconductors. Much higher resolution and spin resolvable function of the ARPES technique are highly demanded in the study of condensed matters especially the cuprates superconductors of which the interested energy scale is tens of meV below Fermi level. The development of laser frequency doubling technology, especially the application of KBe2 BO3 F2 recently [1], provided an opportunity to develop new generation of ARPES with ultra-high resolution [2]. After successfully building vacuum ultraviolet (VUV) laser-based ARPES system, based on the newly developed ultra-violet laser system, we designed and developed a spin resolved ARPES system with high energy resolution, a time-of-flight ARPES system and a photon energy tunable laser on the ARPES system. Figure 2.1 is the 3D simulated blueprint of the three ARPES systems in our lab. Based on the 3D modeling, we have completed the installation of the spin resolved ARPES and the time-of-flight ARPES system which will be introduced in this chapter in detail. This chapter will mainly focus on three parts: (1) The principle of ARPES; (2) The development of VUV laser-based ARPES and (3) The development of spin resolved ARPES, time-of-fight ARPES and tunable laser-based ARPES.
2.2 The Principle of ARPES [3] Photoemission experiments are based on photoelectric effect which was discovered by Hertz in 1887 [4] and fully explained by Einstein’s photoelectric effect equation W. Zhang, Photoemission Spectroscopy on High Temperature Superconductor, Springer Theses, DOI 10.1007/978-3-642-32472-7_2, © Springer-Verlag Berlin Heidelberg 2013
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2 Angle-Resolved Photoemission Spectroscopy
Fig. 2.1 The 3D modeling of the three distinctive ARPES system
in 1905 [5]. Based on the satisfaction of sudden [6] and adiabatic [7] approximation, photoelectron spectroscopy is a technique that probes the single-particle spectral function in solid materials directly.
2.2.1 Brief Description of ARPES If the incident photon energy is higher than the work function of materials, electrons in the top several or tens of atom layers will be stimulated outside the material, and the energy of the outgoing photoelectrons could be calculated by the following equation [5] Ekin = hν − Φ − EB
(2.1)
Usually, the work function in materials is 4∼5 eV so that the photon energy should be higher than 5 eV in photoemission exp
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