Quantum Matter Seminar

Using circularly-polarized light to control quantum matter is a highly intriguing topic in physics, chemistry and biology. Antiferromagnets (AFMs) have zero net magnetization, so AFM domains are immune to perturbing magnetic field. This leads to the prospect of robust magnetic storage. However, this robustness also means that manipulating fully-compensated AFM order is extremely difficult. We report the surprising observation of helicity-dependent optical control of fully-compensated antiferromagnetic (AFM) order in 2D even-layered MnBi2Te4, a topological Axion insulator no magnetization. We demonstrated helicity-dependent optical creation of AFM domain walls by double induction beams and the direct reversal of AFM domains by ultrafast pulses. The control and reversal of AFM domains and domain walls by light helicity have never been achieved in any fully-compensated AFM. To understand this optical control, we studied an AFM circular dichroism (CD) proportional to the AFM order, which only appears in reflection but is absent in transmission. We showed that the optical control and CD both arise from the optical Axion electrodynamics. The Axion induction provides the possibility to optically control a family of PT-symmetric AFMs such as Cr2O3, even-layered CrI3, and possibly pseudo-gap state in cuprates. If time allows, I will also talk about our recent observation of the quantum metric induced Hall effect.

Reference:

J. Qiu, et al. "Axion optical induction of antiferromagnetic order" Nature Materials s41563-023-01493-5 (2023).

A. Gao et al. "Quantum metric nonlinear Hall effect in a topological antiferromagnetic heterostructure" Science 381, 181-186 (2023).