A hunt for topological quasi particles inside crystals

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Sonja Holm-Dahlin


University of Copenhagen


DKK 1,538,180




Reintegration Fellowships


At CERN, new particles are found by crushing ions into each other at the highest energies accessible to humans. In this project, we want to search for novel quasi-particles at ultra low energies inside crystals. The theoretically predicted magnons that we wish to find are protected against decay by their quantum symmetry and should exist in magnetically frustrated systems. Antiferromagnetism (AFM) is a type of magnetic order where unpaired electron spins strive to point in opposite directions to each other, forming an up-down-up-down pattern inside the crystal structure. If AFM spins are placed in triangular structure it is impossible to fulfill the up-down relationship between all spins and the system becomes magnetically frustrated. It is here our search for the new particle begins.


Recent theoretical work suggests that it is possible to find a new type of magnetic excitation (magnon), that can only travel in one direction. These magnons are protected against decay by their quantum symmetry. The long lifetime of the unidirectional magnon can enable spin-based information transfer and play an important role in the development of new energy-efficient computers using spin-based electronics. Furthermore, the project will give us a better fundamental understanding of the physical properties of our universe and help expand a new research area within condensed matter physics.


A range of magnetic materials will be synthesized in collaboration with Prof. Ulla Gro Nielsen from SDU, who is a leading expert in growing ultra pure samples using the redox hydrothermal method. Other materials will be prepared using a mirror-furnace set-up at Lund University. The successfully synthesized materials will be tested for quality and magnetic properties using e.g. NMR spectroscopy. The best samples will be taken to international neutron facilities where I will attempt to measure excitation signature of the predicted quasi particle using neutron spectroscopy. The analysis of the complex neutron data will be performed in collaboration with Prof. Kim Lefmann from UCPH. Our scientific results will be published in peer-reviewed scientific journals.

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