arXiv subjects

John T. Fourkas

Publications and source records attributed to John T. Fourkas.

3 recordsLinked to original sources

arXiv2026

Correlated Plasmonic Excitation in Twisted Nematic Plasmonic Superlattices

Superlattices with twisted configurations, such as moire lattices, have recently been extensively exploited for their unique electronic, magnetic, and optical properties. One remarkable feature of nanoscale twisted superlattices is the distinct lattice symmetries and the continuous phase transitions between periodic or aperiodic phases, representing a unique opportunity to study many emerging physical phenomena. Here, we report a correlated light and matter interaction between the collective polarization effect of nematic plasmonic superstructures and the plasmonic excitation of individual constituent nanorods in reconfigurable twisted plasmonic superlattices. Using hybrid Fe3O4 and Au nanorods as building blocks, we assembled plasmonic nematic liquid crystals with unidirectionally aligned nanorods, which could be further assembled into moire plasmonic lattices through a vertical stacking assembly method. A twist angle dependent plasmonic excitation is recognized in the twisted bilayer of two plasmonic superlattices, featuring enhanced transverse and longitudinal plasmonic excitation at a twisting angle of 0 degree and 90 degree, respectively. Such correlated plasmonic excitation in twisted plasmonic superstructures is induced by the correlation between the collective polarization effect of the liquid crystal phases and the anisotropic plasmonic excitation of individual nanorods. The magnetic orientation control allows for precise alignment of hybrid Fe3O4 and Au nanorods in polymer substrates and enables the coding of nematic domains and plasmonic patterns in each sublattice. The correlated plasmonic excitation and light polarization create reconfigurable photonic moire superlattices with well-defined domain colors, feature sizes, periodicities, symmetries, and dimensions determined by twist angles and displacements in the twisted plasmonic lattices.

cond-mat.mtrl-sci↗

arXiv2024

Molecular Fingerprints of Ice Surfaces in Sum Frequency Generation Spectra: a First Principles Machine Learning Study

Understanding the molecular-level structure and dynamics of ice surfaces is crucial for deciphering several chemical, physical, and atmospheric processes. Vibrational sum-frequency generation (SFG) spectroscopy is the most prominent tool for probing the molecular-level structure of the air--ice interface as it is a surface-specific technique, but the molecular interpretation of SFG spectra is challenging. This study utilizes a machine-learning potential, along with dipole and polarizability models trained on ab initio data, to calculate the SFG spectrum of the air--ice interface. At temperatures below ice surface premelting, our simulations support the presence of a proton-ordered arrangement at the Ice Ih surface, similar to that seen in Ice XI. Additionally, our simulations provide insight into the assignment of SFG peaks to specific molecular configurations where possible and assess the contribution of subsurface layers to the overall SFG spectrum. These insights enhance our understanding and interpretation of vibrational studies of environmental chemistry at the ice surface.

physics.chem-ph↗

arXiv2017

Coupling emission from single localized defects in 2D semiconductor to surface plasmon polaritons

Coupling of an atom-like emitter to surface plasmons provides a path toward significant optical nonlinearity, which is essential in quantum information processing and quantum networks. A large coupling strength requires nanometer-scale positioning accuracy of the emitter near the surface of the plasmonic structure, which is challenging. We demonstrate the coupling of single localized defects in a tungsten diselenide (WSe2) monolayer self-aligned to the surface plasmon mode of a silver nanowire. The silver nanowire induces a strain gradient on the monolayer at the overlapping area, leading to the formation of localized defect emission sites that are intrinsically close to the surface plasmon. We measure a coupling efficiency with a lower bound of 39% from the emitter into the plasmonic mode of the silver nanowire. This technique offers a way to achieve efficient coupling between plasmonic structures and localized defects of 2D semiconductors.

cond-mat.mes-hall↗