arXiv subjects

Joseph L. Spellberg

Publications and source records attributed to Joseph L. Spellberg.

3 recordsLinked to original sources

arXiv2026

Spatiotemporal Visualization of Long-Range Anisotropic Plasmon Polaritons in Hyperbolic MoOCl2

Manipulating light at the nanoscale with minimal loss remains a central challenge for nanophotonic technologies that can be tackled by using the direction-dependent polariton modes supported by anisotropic materials. Although best known for their highly confined polaritons, hyperbolic materials can also host long-range directional polaritons, whose direct observation has remained challenging as it requires experimental techniques that combine nanometre and femtosecond spatial and temporal resolution, respectively. Here, we use time-resolved photoemission electron microscopy for direct nanoscale visualization of long-range anisotropic plasmon polariton (LRAPP) dynamics on a flake of the van der Waals hyperbolic material molybdenum oxydichloride. We directly image plasmon polaritons with propagation lengths larger than 10 $μ$m, exhibiting an approximately three times longer propagation length and intrinsically lower optical loss than short-range polaritons previously reported on the same material. By tracking the spatiotemporal evolution of LRAPPs, we determine their phase and group velocities at the nanoscale and directly observe their reflections at flake edges. These results establish molybdenum oxydichloride as a versatile platform for integrated nanophotonics, supporting both low-loss directional transport and deeply subwavelength field confinement within a single natural material, in the visible spectral range.

physics.optics↗

arXiv2025

Wrinkle Mediated Phase Transitions in In$_2$Se$_3$

Crystalline phase transitions in two-dimensional materials enable precise control over electronic and ferroic properties, making them attractive materials for memory and energy storage applications. In$_2$Se$_3$ is particularly promising because its $α$ and $β'$ phases are both stable at room temperature but exhibit distinct ferroic behaviors. However, achieving reliable reversible switching between these states remains challenging. Here, we show that controlled $β'\rightarrowα$ phase transitions in 2D In$_2$Se$_3$ become accessible through laser-induced wrinkling, establishing a room-temperature approach for manipulating ferroic states in In$_2$Se$_3$ thin films. Combined with thermal annealing for phase recovery, this approach eliminates cryogenic steps and mechanical perturbation while harnessing accumulated internal strain to generate multiphase heterostructures and direct domain reorganization. This pathway for phase transitions in In$_2$Se$_3$ opens the door for further development in ferroic device architectures and phase-change memory technologies.

cond-mat.mtrl-sci↗

arXiv2022

Nano-imaging of the edge-dependent optical polarization anisotropy of black phosphorus

The electronic structure and functionality of 2D materials is highly sensitive to structural morphology, opening the possibility for manipulating material properties, but also making predictable and reproducible functionality challenging. Black phosphorus (BP), a corrugated orthorhombic 2D material, has in-plane optical absorption anisotropy critical for applications such as directional photonics, plasmonics, and waveguides. Here, we use polarization-dependent photoemission electron microscopy to visualize the anisotropic optical absorption of BP with 54 nm spatial resolution. We find the edges of BP flakes have a shift in their optical polarization anisotropy from the flake interior due to the 1D confinement and symmetry reduction at flake edges that alter the electronic charge distributions and transition dipole moments of edge electronic states, confirmed with first-principles calculations. These results uncover previously hidden modification of the polarization-dependent absorbance at the edges of BP, highlighting the opportunity for selective excitation of edge states of 2D materials with polarized light.

cond-mat.mes-hall↗