Visualizing electronic band splitting in low-Z altermagnetic MnF2 epitaxial films

A new twist in the field of magnetism has emerged due to a new theory based on spin symmetry, leading to a new class of magnetic materials that share properties of both
antiferromagnets and ferromagnets: the so-called altermagnets. They do not exhibit a net macroscopic magnetization, but a spin-splitted density of states of the electronic bands based on symmetry considerations, without the need of relativistic effects (such as spin orbit coupling) or time-reversal symmetry breaking. The experimental confirmation of this new state of matter is going underway. In this proposal, we aim to enlarge the family of altermagnets by studying a low Z compound, MnF2, and demonstrate electronic band splitting via angle-resolved photoemission and spin resolution. Importantly, if a large spin splitting is observed, it cannot be ascribed to Rashba effects as in other high Z altermagnet candidates. For this purpose have prepared highly crystalline, epitaxial thin films of MnF2 (110) via molecular beam epitaxy, which allows to explore the altermagnetic phase down to two-dimensional limit (few-layer and monolayer thickness regime). The impact of our work is expected to be decisive in these early stages of altermagnetism: First, to experimentally verify the altermagnetic phase in a low Z antiferromagnet is an important step to demonstrate that spin splitting exclusively arises from symmetry considerations and not from SOC effects. Secondly, the occurrence of altermagnetism in the two-dimensional limit is an unexplored terrain that shall enrich the current understanding of this emerging field.