Optical dichroism, valley polarization, and noncollinear spin currents in monolayer altermagnetic Ca(CoN)2

Abstract

Altermagnets, recently recognized as a third class of collinear magnetic materials, have garnered increasing attention in condensed matter physics. In this study, combining first-principles calculations with theoretical analysis, we conduct a comprehensive investigation of the intriguing physical properties of the two-dimensional altermagnetic material Ca(CoN)2. We demonstrate that monolayer Ca(CoN)2 is a semiconductor characterized by spin-split, nonrelativistic band structures, featuring a pair of valleys located at the time-reversal invariant momenta X and Y points. These valleys are interconnected through crystal symmetries rather than time-reversal symmetry and exhibit opposite Berry curvature. We find that the system exhibits valley-contrasting optical circular and linear dichroism. Moreover, we show that the application of uniaxial strain can effectively induce valley polarization, while finite carrier doping gives rise to piezomagnetic responses. In addition, noncollinear spin currents are found to be generated under an applied in-plane electric field. These results reveal rich valley and spin phenomena in monolayer Ca(CoN)2, underscoring its promising potential for future applications in valleytronics, spintronics, and multifunctional nanoelectronic devices.