Embargoed until 2025-04-02
Author
Date
2024Type
- Doctoral Thesis
ETH Bibliography
yes
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Abstract
The absence of symmetries has a significant impact on physics, particularly in chiral molecules or crystals lacking mirror symmetry. When an electric charge interacts with such chiral materials, the spin of the charge aligns even at room temperature. This spin polarization is known as chirality-induced
spin selectivity (CISS). Although the exact mechanism behind the effect remains unclear, it may have played a role in the origin of life and significantly impacts biological processes. The effect has potential applications in chemical catalysis, renewable energy, and quantum technologies.
This doctoral thesis aims to elucidate the key mechanism behind CISS surface potential changes upon toggling the enantiomer or magnetic polarization of the substrate. For the first time, chiral α-helical polypeptide films are investigated with time-resolved Kelvin-probe atomic force microscopy to probe the dynamics of the surface potential and a CISS quantum capacitance. This discovery of the CISS quantum capacitance leads to the conclusion that CISS is a persistent effect and paths the way to a fundamental reinterpretation of the CISS effect.
The major break-through of this thesis is based on the observation, that a PT --symmetry is present in all CISS experiments: flipping the orientation of the magnetic polarization (T -transform) or the enantiomer (P-transform) changes the observable. However, simultaneously changing the magnetization and enantiomer (PT -transform) does not impact the experimental outcome. Combining this pattern with CPT -invariance leads to non-Hermitian quantum mechanics. Applying these ideas to the non-relativistic limit of the Dirac equation, a new Schrödinger equation correction term is derived that describes many CISS-related phenomena.
Under this PT -theory, the CISS surface potential and quantum capacitance suggest a persistent current within the chiral materials. The bound states in a triangular quantum well penetrate the chiral molecules to different depths depending upon the experimental parameters. The correction term leads to a spin texture of this bound quantum mechanical state, with its energy dependent on the chirality of the molecule and the magnetization of the substrate.
So far, other experimental CISS observations can be qualitatively explained similarly. In order to further investigate the PT-theory quantitative dynamic experiments are required. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000666882Publication status
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Publisher
ETH ZurichSubject
Kelvin probe force microscopy; chirality-induced spin selectivity; quantum capacitance; spinterface; non-Hermitian systems; SPIN SYSTEMS (MOLECULAR PHYSICS); PeptideOrganisational unit
03444 - Stemmer, Andreas / Stemmer, Andreas
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ETH Bibliography
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