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Phonon Magnetic Moments and Angular Momentum in Flexible Framework Materials

Project description

Getting at what is behind the exotic vibrations that spin atoms in circles

The quantum world is made up of fundamental units, whether matter particles, packets of light or even individual particle-like vibrations in solids called phonons. While vibrations are typically more of an up-and-down, back-and-forth type of movement, it turns out that phonons that cause atoms to move in circles can also have both mechanical and electromagnetic spin. Although typically of very small magnitude, the spins may be amplified in certain materials. This could make them easier to characterise, perhaps revealing new quantum phenomena. The EU-funded PhononMoments project will apply advanced computational and theoretical methods to the study of the forced and natural circular motion of atoms in these materials for insight.

Objective

This project will study how the magnetic moments and orbital angular momenta of phonons are related to chemical structure, electronic structure, and to each other. Phonons, which are particle-like vibrational excitations in solids, are not normally considered to have an angular momentum (a mechanical spin) or a magnetic moment (an electromagnetic spin). However, it has recently been discovered that vibrations that cause atoms to move in circles can in fact have these properties, although their magnitudes are thought to be extremely small in conventional materials. We aim to study these exotic properties of phonons in flexible framework materials, which are materials which combine extreme stiffness in some directions with extreme compliance in others. This combination can give rise to very low energy vibrational modes, which results in very large motions of the atoms, and therefore we expect flexible frameworks to have much larger phonon magnetic moments and angular momenta than in conventional materials.

Our goal is to discover materials with very large phono-magnetic effects, ideally sufficiently large that they can be measured using existing experimental techniques. Large phono-magnetic effects would also allow the magnetic moment of the phonon to interact with magnetism due to the spins of electrons, leading to a heretofore undescribed physical interaction which could be useful in the study of magnetic materials. We will use computational and theoretical methods to study both materials where the circular motions of atoms require external stimulus to occur, and also chiral materials where the atoms can naturally move in circles. In this latter case, the introduction of magnetic order in the material can break the symmetry between phonons of one handedness and the other, potentially leading to emergent bulk effects such as a thermally driven angular momentum of the crystal as a whole.

Coordinator

EIDGENOESSISCHE TECHNISCHE HOCHSCHULE ZUERICH
Net EU contribution
€ 191 149,44
Address
Raemistrasse 101
8092 Zuerich
Switzerland

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Region
Schweiz/Suisse/Svizzera Zürich Zürich
Activity type
Higher or Secondary Education Establishments
Links
Total cost
€ 191 149,44