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Topology and magnetism
In magnetic topological materials, the electronic and magnetic properties of the system are often intricately coupled. Specifically, regions with spatially varying magnetization (e.g., domain walls or non-collinear spin textures) provide an exciting platform to study how Berry curvature effects are manifested and potentially controlled in real space. We are currently developing novel visualization techniques that will enable us to detect subtle changes in both magnetization and Berry curvature with sub-micrometer spatial resolution.
Collective modes
Collective modes (phonons, magnons, polaritons, etc.) serve as critical signature for understanding quantum materials. Using ultrafast (~100 femtoseconds) time-resolved microscopy, we investigate how multiple degrees of freedom couple to generate novel quasiparticles and collective modes in the time domain. Probing the local variations and transport properties of these collective mode reveals phenomena often inaccessible via conventional techniques. While laser pulses can serve as weak perturbations to initiate excitations, their strong electric fields can also induce nonequilibrium changes in the free energy landscape, realizing a novel ground state .
Spin wave propagation
Spin waves, or magnons, have emerged as a promising method for transmitting coherent spin information over macroscopic distances (greater than a few micrometers). Despite ongoing research, key questions remain about the speed and wavelength of actively launched spin waves, as well as the types of spin interactions that influence their transport dynamics. Recent findings have shown that long-range dipolar interactions can significantly affect spin wave dispersion, even in antiferromagnets that do not exhibit net magnetization. By employing a combination of optical, electro-optic, and scattering probes, we aim to deepen our understanding of how both exchange and long-range interactions impact spin wave transport properties.
Experimental techniques
Developing new experimental probes and improving existing ones are crucial for gaining a deeper understanding of quantum materials. By leveraging a combination of optical, photothermal, and thermoelectric techniques, we measure the dynamical properties of the ground state and excitations of quantum matter.
Magneto-optic microscopy: Magneto-optical effects reveal critical information about broken symmetry in quantum materials. For instance, the magneto-optic Kerr effect (MOKE) probes the breaking of time-reversal symmetry, while linear dichroism and birefringence measure rotational symmetry breaking. Combining these techniques with high spatial resolution (sub-micron) allows us to visualize local variations of magnetization and in-plane anisotropy in ordered systems. We are currently working to improve the spatial resolution to ~100 nanometers.
Anomalous Nernst microscopy
Thermal diffusivity
Optical pump-probe microscopy
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