A5066641633- Plasmonic and Surface Plasmon Research
- Photonic Crystals and Applications
- Mechanical and Optical Resonators
- 2D Materials and Applications
- Strong Light-Matter Interactions
- Graphene research and applications
- Thermal Radiation and Cooling Technologies
- Quantum Dots Synthesis And Properties
- Solid-state spectroscopy and crystallography
- Metamaterials and Metasurfaces Applications
- Nanowire Synthesis and Applications
- Gold and Silver Nanoparticles Synthesis and Applications
- Supramolecular Self-Assembly in Materials
- Photonic and Optical Devices
- Organic and Molecular Conductors Research
- CO2 Reduction Techniques and Catalysts
- Electronic and Structural Properties of Oxides
- Quantum Electrodynamics and Casimir Effect
- Sensor Technology and Measurement Systems
- Topological Materials and Phenomena
- Nonlinear Optical Materials Studies
- Molecular Junctions and Nanostructures
- Advanced Condensed Matter Physics
- Chalcogenide Semiconductor Thin Films
- Advanced Fiber Laser Technologies
Columbia University
2018-2023
University of California, San Diego
2018
Graphene is an atomically thin plasmonic medium that supports highly confined plasmon polaritons, or nano-light, with very low loss. Electronic properties of graphene can be drastically altered when it laid upon another layer, resulting in a moir\'e superlattice. The relative twist angle between the two layers key tuning parameter interlayer coupling thus obtained twisted bilayer (TBG). We studied propagation polaritons TBG by infrared nano-imaging. discovered atomic reconstruction occurring...
Abstract Photonic crystals are commonly implemented in media with periodically varying optical properties. enable exquisite control of light propagation integrated circuits, and also emulate advanced physical concepts. However, common photonic unfit for in-operando on/off controls. We overcome this limitation demonstrate a broadly tunable two-dimensional crystal surface plasmon polaritons. Our platform consists continuous graphene monolayer back-gated nano-structured gate insulators....
Natural hyperbolic materials with dielectric permittivities of opposite signs along different principal axes can confine long-wavelength electromagnetic waves down to the nanoscale, well below diffraction limit. Confined coupled phonons in dielectrics including hexagonal boron nitride (hBN) and α-MoO3 are referred as phonon polaritons (HPPs). HPP dissipation at ambient conditions is substantial, its fundamental limits remain unexplored. Here, we exploit cryogenic nanoinfrared imaging...
Abstract Ferroelectricity, a spontaneous and reversible electric polarization, is found in certain classes of van der Waals (vdW) materials. The discovery ferroelectricity twisted vdW layers provides new opportunities to engineer spatially dependent optical properties associated with the configuration moiré superlattice domains network domain walls. Here, we employ near-field infrared nano-imaging nano-photocurrent measurements study minimally WSe 2 . ferroelectric are visualized through...
Abstract Van-der Waals (vdW) atomically layered crystals can act as optical waveguides over a broad range of the electromagnetic spectrum ranging from Terahertz to visible. Unlike common Si-based waveguides, vdW semiconductors host strong excitonic resonances that may be controlled using non-thermal stimuli including electrostatic gating and photoexcitation. Here, we utilize waveguide modes examine photo-induced changes excitons in prototypical semiconductor, WSe 2 , prompted by femtosecond...
Topological spin textures are field arrangements that cannot be continuously deformed to a fully polarized state. In particular, merons topological characterized by half-integer charge ±1/2 and vortex-like swirling patterns at large distances. Merons have been studied previously in the context of cosmology, fluid dynamics, condensed matter physics plasmonics. Here, we visualized optical angular momentum phonon polaritons resembles nanoscale meron textures. Phonon polaritons, hybrids infrared...
When light-matter polaritons travel in periodic media, they acquire properties akin to Bloch quasi-particles crystals.
Significance Nonlinear optics in topological semimetals is a burgeoning field of research with an expanding list new materials but limited choice probes. We devised, modeled, and implemented approach for investigating nonlinear at the nanoscale metallic tip. Far-field are diffraction-limited probe in-plane response only. Our tip-based circumvents diffraction limit provides strong enhancement both out-of-plane fields. therefore gain access to complete tensors including components not...
Many of the existing electrochemical catalysts suffer from poor selectivity, instability, and low exchange current densities. These shortcomings call for a comprehensive exploration catalytic processes at fundamental nanometer length scale levels. Here we exploit infrared (IR) nanoimaging nanospectroscopy to directly visualize reactions on surface Cu2O polyhedral single crystals with nanoscale spatial resolution. Nano-IR data revealed signatures this common catalyst after reduction carbon...
Abstract Natural hyperbolic materials with dielectric permittivities of opposite sign along different principal axes can confine long-wavelength electromagnetic waves down to the nanoscale, well below diffraction limit. This has been demonstrated using phonon polaritons (HPP) in hexagonal boron nitride (hBN) and -MoO3, among other materials. However, HPP dissipation at ambient conditions is substantial its fundamental limits remain unexplored1,2. Here, we exploit cryogenic nano-infrared...
Abstract Excitons play a dominant role in the optoelectronic properties of atomically thin van der Waals (vdW) semiconductors. These excitons are amenable to on-demand engineering with diverse controls, including dielectric screening, interlayer hybridization, and moiré potentials. However, external stimuli frequently yield heterogeneous excitonic responses at nano- meso-scales, making their spatial characterization conventional diffraction-limited optics formidable task. Here, we use...
Abstract The osmate pyrochlore Cd 2 Os O 7 supports an antiferromagnet insulator ground state with all-in/all-out (AIAO) spin ordering at low temperature. Above 225 K, becomes a paramagnetic metal whereas the mechanism of this metal-to-insulator transition (MIT) remains elusive. In letter, we use cryogenic near-field technique operating terahertz frequencies to study evolution low-energy response across MIT. We observed systematic variation magnitude nano-THz signal transition, consistent...
Ferroelectricity, a spontaneous and reversible electric polarization, is found in certain classes of van der Waals (vdW) material heterostructures. The discovery ferroelectricity twisted vdW layers provides new opportunities to engineer spatially dependent optical properties associated with the configuration moir\'e superlattice domains network domain walls. Here, we employ near-field infrared nano-imaging nano-photocurrent measurements study minimally WSe2. ferroelectric are visualized...