PhD Thesis Defense: Louis Alaerts

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"First-principles studies of electrical polarization effects in ferroelectrics, antiferroelectrics, and defects"

Abstract

Over the last few decades, density functional theory (DFT) has emerged as a formidable tool in the field of computational material science. Not only has it become a complementary method approach to experiments by rationalizing the many complex properties of materials but its formidable predictive power can also be used to identify the most promising candidates for specific applications.

Point defects in semiconductors have become an important platform for the development of quantum networks due to their ability to act as spin-photon interfaces. Spectral diffusion, the broadening of the optical emission line, can significantly impact the performance of these defect-based quantum networks. One of the main sources of spectral diffusion is the Stark shift, which arises as the result of the coupling between the dipole moment change upon electronic transition and stray electric fields. In the first part of this thesis, I will discuss our work on the development of a methodological framework through which the Stark shift of defects can be evaluated directly from first principles. We benchmarked our approaches on the nitrogen-vacancy center in diamond and discussed the challenges associated with each method. Then, we demonstrate the effectiveness of our methodology by studying the Stark shift of the T center in silicon, a promising defect that has recently been integrated into photonic devices.

In the second part of this thesis, I will present some of our work on the high-throughput search of new ferroelectrics. Ferroelectrics are materials with a spontaneous, switchable polarization and have many potential applications in electronic devices. We used the soft-mode theory of ferroelectricity to screen hundreds of materials in a phonon database. I discuss some of our findings and lessons from this work by presenting some of our candidates, among which some have been experimentally synthesized. We also demonstrate that this approach can be used to discover new antiferroelectrics, materials with a non-polar ground state that can be driven into a polar phase by an electric field induced transition. Finally, we provide some perspectives about the methodological challenge associated with the search of new ferroelectrics and antiferroelectrics.

Thesis Committee

• Prof. Geoffroy Hautier (chair)
• Prof. Will Scheideler
• Prof. Phillipe Ghosez (ULiège)
• Prof. Mattias Fitzpatrick

Contact

For more information, contact Thayer Registrar at thayer.registrar@dartmouth.edu.