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High Temperature Electron-Phonon and Magnon-Phonon Interactions


Yang, Fred Chae-Reem (2019) High Temperature Electron-Phonon and Magnon-Phonon Interactions. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/1KP5-CJ98.


Computational materials discovery and design has emerged in order to meet the surge in demand for new materials for applications ranging from clean alternative energy to human welfare. This acceleration of materials discovery is exhilarating, but the applications of new advanced materials can be limited by their thermodynamic stability. Accurate calculations of the Gibbs free energy, a measure of thermodynamic stability, require a deep understanding of atomic vibrations, a main source of entropy in materials. This deep understanding of atomic vibrations requires us to treat phonons (quantized lattice vibrations) beyond the harmonic model by considering their interactions with various excitations. In this thesis, I present the effects of high temperature interactions of phonons with electrons and magnetic excitations on the thermodynamics of FeTi, vanadium, and Pd3Fe.

A combination of ab initio calculations, inelastic neutron scattering (INS), and nuclear resonant inelastic x-ray scattering (NRIXS) showed an anomalous thermal softening of the M5 phonon mode in B2-ordered FeTi and a thermal stiffening of the longitudinal acoustic N phonon mode in body-centered-cubic vanadium. Computational investigations involving electronic band unfolding were performed to identify the nesting features on Fermi surfaces crucial to high temperature electron-phonon interactions in FeTi and vanadium. These investigations showed that the Fermi surface of FeTi undergoes a novel thermally driven electronic topological transition (ETT), in which new features of the Fermi surface arise at elevated temperatures. This ETT was also observed in vanadium, but the effects were overtaken by the thermal smearing of the Fermi surface that decreased the rate of electron-phonon scattering.

Iron phonon partial densities of states of Pd3Fe were measured with NRIXS from room temperature through the Curie transition at 500 K. The experimental results were compared to ab initio spin-polarized calculations that modeled the finite-temperature thermodynamic properties of Pd3Fe with magnetic special quasirandom structures (SQSs) of magnetic moments. The scattering measurements and first-principles calculations showed that the iron partial vibrational entropy is close to what is predicted by the quasiharmonic approximation owing to a cancellation of effects: phonon-phonon and magnon-phonon interactions approximately cancel a ferromagnetic optical phonon stiffening.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Materials thermodynamics; electron-phonon interaction; electronic structure; fermi surface; band unfolding; electronic topological transition; magnon-phonon interaction
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Materials Science
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Fultz, Brent T.
Thesis Committee:
  • Minnich, Austin J. (chair)
  • Bernardi, Marco
  • Schwab, Keith C.
  • Fultz, Brent T.
Defense Date:25 March 2019
Funding AgencyGrant Number
Department of Energy (DOE)DE-NA-0002006
Record Number:CaltechTHESIS:03272019-174351662
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Chapter 2. adapted for Chapter 4.
Yang, Fred Chae-Reem0000-0002-5615-5170
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11433
Deposited By: Chae-Reem Yang
Deposited On:01 May 2019 23:51
Last Modified:04 Oct 2019 00:25

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