Publications

Integrating two-dimensional van der Waals magnets into field-effect spintronic devices requires robust charge stability and tunable spin responses. In this study, we investigate the electronic, topological, magnonic, and magneto-optical properties of the strain-engineered ferromagnetic $\text{CrSiSe}_3$ monolayer under out-of-plane external electric fields by using first-principles calculations. We find that for this material, the intrinsic charge sector, including the indirect band gap, charge Berry curvature, optical conductivities, and magneto-optical Kerr effect spectra, exhibits exceptional robustness against applied fields up to 0.3 V/Å. Conversely, the spin degrees of freedom demonstrate highly sensitive tunability. Electrostatic gating significantly modulates the spin Berry-like curvature, driving a non-monotonic enhancement in the spin Hall conductivity. Furthermore, external fields effectively tune collective magnon excitations by modifying microscopic Heisenberg exchange interactions. Such coexistence of robust charge immunity and flexible spin manipulation establishes the strained $\text{CrSiSe}_3$ monolayer as a promising platform for stable spintronic devices.

Planar cavity magnonics has been developed mainly for a single magnetic film, leaving multilayer behavior in spatially resolved cavity scattering largely unexplored. Here, we introduce a double layer planar cavity with two magnetic films embedded in the same microwave cavity to derive a full two-film scattering theory in the macrospin ($J = 0$) limit and recover the exact zero-gap half-thickness limit, thereby benchmarking the model against the known one-film result. We find that the double layer model actively enables geometry-controlled bright-channel enhancement, demonstrating that the magnon-photon coupling depends on spatial placement rather than just total magnetic volume. Antinode-compatible placements increase the coupling, while node-compatible placements suppress it. Weak symmetry breaking also transfers finite cavity weight to a mode dark in the symmetric limit, producing an additional branch without destroying the main avoided crossing. Finally, a reduced multimode theory for $J\neq 0$ predicts family-resolved bright and dark channels for odd standing-spin-wave modes.

We theoretically investigate the optical absorption of an undoped graphene monolayer when put in a one-dimensional multilayer stack. Using the transfer matrix method, we perform numerical simulations and derive explicit analytical formulas for the optical absorption of the graphene monolayer at the center of the dielectric stack and find that the optical absorption uniquely depends on repetition number ($r$) and the unit layers structure. When sandwiched between unit layers structure composed of three dielectric materials (referred to as the "ABC" structure) with even values of $r$, the graphene monolayer absorbs $2.3$% of visible to near-infrared light. This behavior is the same as if graphene were free-standing, not sandwiched between the dielectric stack. In contrast to that situation, in the ABC structure with odd values of $r$, also when the graphene monolayer is sandwiched between four materials (the "ABCD" structure) with any values of $r$, we can obtain optical absorption as large as $50$% at particular refractive indices ($n$) of the constituent dielectric materials. The $50$%-absorption is, in fact, the maximum optical absorption for any undoped monolayer material in the symmetric dielectric stacks. By varying $r$ and $n$ within the ABC or ABCD structures, we can finely adjust the optical absorption of graphene within the range of $0$-$50$%, facilitating precise control for various optoelectronic applications.