Brongersma Group Plasmonics and Photonics at Stanford University

@article{guarneri2025dynamic,

title = {Dynamic Excitonic Beam Switching with Atomically‐Thin Binary Blazed Gratings},

author = {Ludovica Guarneri and Thomas Bauer and Qitong Li and Jung‐Hwan Song and Skyler P Selvin and Ashley P Saunders and Fang Liu and Mark L Brongersma and Jorik van de Groep},

doi = {10.1002/adom.202403257},

year  = {2025},

date = {2025-05-12},

urldate = {2025-05-12},

journal = {Advanced Optical Materials},

volume = {13},

issue = {15},

pages = {2403257},

abstract = {Beam steering metasurfaces are ultra-compact optical coatings that offer on-demand redirection of optical power to specific diffraction orders. To achieve this, spatial gradients are commonly introduced in the phase of light scattered by plasmon or Mie resonant nanoparticles within the metasurface grating's unit cell. However, these phase gradients are oftentimes difficult to tune post-fabrication. Recently, excitons in monolayer 2D semiconductors have emerged as a new metasurface building block, due to their strong and electrically-tunable resonant light-matter interaction. These 2D excitonic metasurfaces offer the tantalizing prospect of beam switching within a single monolayer. Here, it is demonstrated how the 2D analog of binary blazed gratings enables such beam switching by mere nanopatterning of a large monolayer WS2, even though nanoscale ribbons of WS2 do not support geometrical resonances. By introducing a gradient in the nanoribbon width within the metasurface unit cell, an amplitude gradient combined with a small phase gradient in the scattered fields results in asymmetric diffraction efficiencies. Using a scattered-field analysis, it is shown that these gradients can be further engineered via interference effects with the substrate reflection. Finally, the electrical tunability of the exciton resonance is leveraged to achieve selective and dynamic beam switching with an atomically-thin metasurface.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{guarneri2024temperature,

title = {Temperature-Dependent Excitonic Light Manipulation with Atomically Thin Optical Elements},

author = {Ludovica Guarneri and Qitong Li and Thomas Bauer and Jung-Hwan Song and Ashley P Saunders and Fang Liu and Mark L Brongersma and Jorik van de Groep},

doi = {10.1021/acs.nanolett.4c00694},

year  = {2024},

date = {2024-04-05},

journal = {Nano Letters},

abstract = {Monolayer 2D semiconductors, such as WS2, exhibit uniquely strong light\textendashmatter interactions due to exciton resonances that enable atomically thin optical elements. Similar to geometry-dependent plasmon and Mie resonances, these intrinsic material resonances offer coherent and tunable light scattering. Thus far, the impact of the excitons’ temporal dynamics on the performance of such excitonic metasurfaces remains unexplored. Here, we show how the excitonic decay rates dictate the focusing efficiency of an atomically thin lens carved directly out of exfoliated monolayer WS2. By isolating the coherent exciton radiation from the incoherent background in the focus of the lens, we obtain a direct measure of the role of exciton radiation in wavefront shaping. Furthermore, we investigate the influence of exciton\textendashphonon scattering by characterizing the focusing efficiency as a function of temperature, demonstrating an increased optical efficiency at cryogenic temperatures. Our results provide valuable insights into the role of excitonic light scattering in 2D nanophotonic devices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}