PHYS07200604007 Manas Kumar Dala - Homi Bhabha National ...

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Experimental Techniques 24 2.1 Introduction Spectroscopic methods are some of the most powerful techniques for studying the electronic structure of solids. This chapter is intended to describe the details of the different spectroscopic techniques which have been used in this thesis work. 2.2 Photoemission Spectroscopy 2.2.1 Basic principle The principle of photoemission spectroscopy is based on the principle of photoelectric effect. The photoelectric effect was first discovered by the German Physicist Heinrich Hertz [1] in 1887 and latter explained by Albert Einstein [2] in 1905 as a manifestation of the quantum nature of light. Figure 2.1: Principle of a modern photoemission experiment. The photon source is either UV light or X-ray, which hit the sample surface under an angle ψ with respect to the surface normal. The kinetic energy E kin of the photoelectrons can be analysed by use of electrostatic analysers. When light is incident on a sample, electron can absorb the photon and escape from the sample with a maximum kinetic energy as shown in the Fig. 2.1. If a photon having energy hν is absorbed by the electron of binding energy E B , then the kinetic energy E kin of the electron is given by, E kin = hν − E B − φ, (2.1) where φ is the work function of the material. The resulting photoelectron spectra is a plot of the number of emitted electrons versus their kinetic energy, which gives the information about the electronic structure of the material. Fig. 2.2 shows
Experimental Techniques 25 Figure 2.2: Schematic view of the energetics of the photoemission process [3], which gives the relation between the energy levels in a solid and the electron energy distribution produced by photons of energy hν. The electron energy distribution which can be measured by the analyser as a function of kinetic energy (E kin ) is more conveniently expressed in terms of the binding energy E B when one refers to the density of states inside the solid. schematically how the energy level diagram and the energy distribution of photoemitted electrons relate to each other. 2.2.2 Theoretical interpretation of photoemission There have been many important theoretical studies to describe and analyse the spectral features in photoemission process [3, 4, 5, 6]. The most general and widely applied theoretical description of the photoemission spectrum is based on using Fermi’s golden rule as a result of perturbation theory in first order. The photo current produced in the photoemission spectroscopy experiment is due to the excitation of electrons from the initial states i with wave function ψ i to the final states f with wave function ψ f by the photon field having vector potential A. According to the Fermi’s Golden Rule,
Page 1 and 2: SPECTROSCOPIC INVESTIGATIONS OF THE
Page 3 and 4: iii To My Parents
Page 5 and 6: Maharana, P. Khare, D. K. Basa, K.
Page 7 and 8: List of Publications/Preprints [1]
Page 9 and 10: Synopsis The perovskite type mangan
Page 11 and 12: to the t 2g and e g spin-up states
Page 13 and 14: Bibliography [1] R. von Helmolt, J.
Page 15 and 16: Contents CERTIFICATE Acknowledgemen
Page 17 and 18: List of Figures 1.1 Temperature dep
Page 19 and 20: 2.2 Schematic view of the energetic
Page 21 and 22: 3.4 O K edge x-ray absorption spect
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Page 37 and 38: Introduction 15 Figure 1.12: Schema
Page 39 and 40: Introduction 17 Figure 1.13: Phase
Page 41 and 42: Bibliography [1] R. von Helmolt, J.
Page 43 and 44: Introduction 21 [31] Damien Saurel,
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Page 59 and 60: Experimental Techniques 37 ∆E = E
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Page 77 and 78: Bibliography [1] H. Hertz, Ann. Phy
Page 79 and 80: Experimental Techniques 57 [35] K.
Page 81 and 82: Chapter 3 Electronic Structure of P
Page 83 and 84: Electronic Structure of Pr 0.67 Ca
Page 95 and 96: Bibliography [1] I. G. Deac, J. F.
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Electronic Structure of Pr 0.67 Ca
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Chapter 4 Electronic Structure of P
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Electronic Structure of Pr 1−x Ca
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Electronic Structure of Ca 0.86 Pr
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Bibliography [1] C. Zener, Phys. Re
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Summary and Conclusions 109 In this
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