Magnetic Birefringence as an Optical Signature of Collinear Altermagnetism

Altermagnets have been established as a separate class of magnetic materials, exhibiting nonrelativistic spin splitting in the absence of spin orbit interaction and net magnetization. While the momentum-dependence of the spin polarization of the band structure is a direct manifestation of the presence of altermagnetic order, its direct experimental detection is challenging.  Moreover, characteristic responses such as the anomalous Hall effect are forbidden by the spin symmetries of these materials without spin-orbit coupling (SOC) and, even in the presence of SOC, only appear for specific moment directions, revealing the necessity to find new signatures that can offer information about the electronic band structure and that can be more accesible to experiments.     

 

In this talk we propose the magnetic birefringence as a direct experimental manifestation of collinear altermagnetism. Using tight binding and realistic simulations, we discuss the role of spin orbit coupling to observe a sizable magnetic birefringence in g-wave and d-wave altermagnets. We also show that the spin contribution is larger than its total orbital angular momentum counterpart. Finally, we demonstrate that this phenomenon can be explicitly connected to a generalized angular momentum quantum geometry, concluding that the behavior of the quantum metric plays a crucial role on this response.