Exploring optical material properties through quantum geometry

Junyeong Ahn, Harvard University
Zoom Seminar
Guang Bian

Understanding and manipulating quantum superposition are important quests in quantum materials research. One exciting direction emerging in the field is to use the geometry of quantum states – the so-called quantum geometry – as a means of characterizing quantum superposition. This approach has successfully characterized various electric and magnetic properties of materials, which are not easily captured by semiclassical approaches. In this seminar, I will first introduce a general theory of the quantum geometry of resonant optical electric-dipole responses in materials. I will discuss the new insights from this quantum-geometric paradigm, guiding us to discover and investigate new optical phenomena. In the second part, I will talk about an intriguing optical response going beyond electric-dipole transitions: a surprising Kerr effect in certain antiferromagnets that are non-quantized but owe their existence to axion electrodynamics. This response has recently been observed in experiments and used for the optical control of antiferromagnets. Finally, I will give an outlook for future directions.