Research Projects

The recent discovery of altermagnets (AM) promises a paradigm shift in condensed matter physics, with implications for both fundamental understanding and technological applications. AM exhibit spin-split electronic bands and broken time-reversal symmetry but have zero net magnetisation, making them highly promising for (opto)-spintronic devices in terms of speed and scalability, However, direct detection of AM typically requires techniques like spin-polarised ARPES which are not widely accessible. Furthermore, despite theoretical predictions, the fundamental excitations of AM: non-degenerate chiral magnons have yet to be observed experimentally. This project aims to address this gap by developing an innovative and broadly accessible methodology for detecting chiral magnons in AM. Our goal is also to determine the symmetry of the magnon band splitting and assess the potential for chiral excitons in these materials. In Raman scattering, two-magnon excitations involve zero net momentum transfer, with the cross section proportional to the polarization’s projection onto the direction of nearest-neighbours. Our hypothesis is that this will enable selective excitation of two-magnon states in symmetric lobes of AM, leading to observable dichroism in the two-magnon density of states. Thus, by controlling the incident polarization and detecting the helicities of scattered light, it will be possible to identify both the presence and symmetry of chiral magnons in AM. Additionally, in materials with strong magnon-phonon-exciton coupling, angular momentum from magnons could transfer to excitons, which we also intend to detect using this approach. The experimental setup will involve a custom-built Raman spectrometer capable of high-resolution, polarization-sensitive measurements. High-quality single crystals of d-wave AM candidates, NiF₂ and CoF₂, will be synthesized using established methods and structurally and magnetically characterized using XRD, SQUID magnetometry, and XMCD. Momentum space mapping will allow us to determine the symmetry of the chiral magnons and excitons. By analysing the helicities of both magnons and excitons, we can estimate the angular momentum transfer between them. Additionally, single-ion calculations will be done to determine the nature of the exciton. If successful, this project will provide the first experimental evidence of chiral magnons in AM filling a significant gap in the understanding of AM and validating their theoretical descriptions. It would also establish polarized Raman scattering as a viable technique for chiral magnon detection, making future studies of AM more practical. Moreover, this methodology could be extended to image AM domains using micro-Raman spectroscopy. Ultimately, the results would offer critical insights towards developing scalable, high-speed spintronic and magnonic devices, with potential applications in ultrafast magnetism and energy efficient devices that utilize the chiral degree of freedom.