Measuring, Interpreting and Translating Electron Quasiparticle - Phonon Interactions on the Surfaces of the Topological Insulators Bismuth Selenide and Bismuth Telluride

 Previously published in hardcover
Besorgungstitel | Lieferzeit:3-5 Tage I
Previously published in hardcover
Colin Howard
1708 g
235x155x0 mm
Springer Theses

1 Introduction
2 Properties of Bi2Se3 and Bi2Te3

2.1 Crystal structure

2.2 Bulk vibrational structure

2.3 Electronic structure

3 Helium atom-surface scattering (HASS)

3.1 The benefits of HASS

3.2 The surface interaction potential

3.3 The kinematics of HASS

3.3.1 Elastic scattering

3.3.2 Inelastic scattering and time-of-flight technique

4 Experimental Apparatus and Technique

4.1 Surface Laboratory facilities

4.2 Source chamber

4.3 Target chamber

4.3.1 Production and monitoring of UHV

4.3.2 Sample manipulator

4.3.3 Sample cleaver

4.3.4 Helium detector

5 Pseudocharge phonon model

5.1 Fundamentals of the model

5.2 Adiabatic approximation, ionic self-terms, and PC self-terms

5.3 Bulk parameters

5.4 Surface parameters

6 HASS results from the surface of Bi2Se3 and Bi2Te3

6.1 Elastic and inelastic scattering results

6.2 Calculation of EPC parameter in the Random Phase Approximation

7 Translating between electron and phonon perspectives

7.1 Motivation

7.2 DFQ Self Energy Formalism

7.3 Computational Results

7.4 Additional Supporting Results

8 Conclusion and future directions

8.1 Summary

8.2 Future work


A Supplemental material for electron self-energy analysis

A.1 Electron Green's function

A.2 Bosonic sums

B Numerical evaluation of the DFQ self energy

B.1 Hole term

B.1.1 Above Dirac point

B.1.2 Below Dirac point

B.2 Particle term

B.2.1 Above Dirac point

B.2.2 Below Dirac point

B.3 Interband transitions


Curriculum Vitae
The thesis presents experimental and theoretical results about the surface dynamics and the surface Dirac fermion (DF) spectral function of the strong topological insulators Bi2Te3 and Bi2Se3. The experimental results reveal the presence of a strong Kohn anomaly in the measured surface phonon dispersion of a low-lying optical mode, and the absence of surface Rayleigh acoustic phonons. Fitting the experimental data to theoretical models employing phonon Matsubara functions allowed the extraction of the matrix elements of the coupling Hamiltonian and the modifications to the surface phonon propagator that are encoded in the phonon self-energy. This allowed, for the first time, calculation of phonon mode-specific DF coupling ni (q) from experimental data, with average coupling significantly higher than typical values for metals, underscoring the strong coupling between optical surface phonons and surface DFs in topological insulators. Finally, to connect to experimental results obtained from photoemission spectroscopies, an electronic (DF) Matsubara function was constructed using the determined electron-phonon matrix elements and the optical phonon dispersion. This allowed calculation of the DF spectral function and density of states, allowing for comparison with photoemission and scanning tunneling spectroscopies. The results set the necessary energy resolution and extraction methodology for calculating from the DF perspective.

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