A5003890796- 2D Materials and Applications
- Plasmonic and Surface Plasmon Research
- Graphene research and applications
- Strong Light-Matter Interactions
- Quantum and electron transport phenomena
- Quantum Electrodynamics and Casimir Effect
- Advanced Fiber Laser Technologies
- Metamaterials and Metasurfaces Applications
- Laser-Matter Interactions and Applications
- Quantum Dots Synthesis And Properties
- Perovskite Materials and Applications
- Photonic Crystal and Fiber Optics
- Nanowire Synthesis and Applications
- Molecular Junctions and Nanostructures
- Rare-earth and actinide compounds
- Mechanical and Optical Resonators
- Topological Materials and Phenomena
- Inorganic Chemistry and Materials
- Photorefractive and Nonlinear Optics
- Cancer-related molecular mechanisms research
- Nonlinear Photonic Systems
- Solid-state spectroscopy and crystallography
- Surface and Thin Film Phenomena
- Photonic and Optical Devices
- Photonic Crystals and Applications
Columbia University
2021-2025
Henan University of Science and Technology
2023
Stony Brook University
2022
Binghamton University
2022
Yale University
2022
Fudan University
2012-2022
State Key Laboratory of Surface Physics
2016-2022
State Key Laboratory of Genetic Engineering
2012
The atomic and electronic structure of intrinsic defects in a WSe_{2} monolayer grown on graphite was revealed by low temperature scanning tunneling microscopy spectroscopy. Instead chalcogen vacancies that prevail other transition metal dichalcogenide materials, arise surprisingly from single tungsten vacancies, leading to the hole (p-type) doping. Furthermore, we found these dominate excitonic emission at temperature. Our work provided first atomic-scale understanding defect excitons paved...
We visualized negative refraction of phonon polaritons, which occurs at the interface between two natural crystals. The polaritons-hybrids infrared photons and lattice vibrations-form collimated rays that display when passing through a planar hyperbolic van der Waals materials: molybdenum oxide (MoO3) isotopically pure hexagonal boron nitride (h11BN). At special frequency ω0, these can circulate along closed diamond-shaped trajectories. have shown polariton eigenmodes regions both positive...
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 control knobs, 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 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...
Plasmon polaritons are formed by coupling light with delocalized electrons. The half-light and half-matter nature of plasmon endows them unparalleled tunability via a range parameters, such as dielectric environments carrier density. Therefore, expected to be tuned when in proximity polar materials since the density is an electrostatic potential; conversely, polariton response might enable sensing polarization. Here, we use infrared nanoimaging nanophotocurrent measurements investigate...
Abstract Exciton polaritons are quasiparticles of photons coupled strongly to bound electron-hole pairs, manifesting as an anti-crossing light dispersion near exciton resonance. Highly anisotropic semiconductors with opposite-signed permittivities along different crystal axes predicted host exotic modes inside the called hyperbolic (HEPs), which confine subdiffractionally enhanced density states. Here, we show observational evidence steady-state HEPs in van der Waals magnet chromium sulfide...
Ultraclean graphene at charge neutrality hosts a quantum critical Dirac fluid of interacting electrons and holes. Interactions profoundly affect the dynamics graphene, which is encoded in properties its electron-photon collective modes: surface plasmon polaritons (SPPs). Here, we show that polaritonic interference patterns are particularly well suited to unveil interactions fluids by tracking time temporal scales commensurate with electronic scattering. Spacetime SPP recorded terahertz (THz)...
Electrons in low-dimensional materials driven out of equilibrium by a strong electric field exhibit intriguing effects that have direct analogues high-energy physics. In this work we demonstrate two these can be observed graphene, leading to relevant implications for light-matter interactions at the nanoscale. For doped Cherenkov emission phonons caused fast flow out-of-equilibrium electrons was found induce direction-dependent asymmetric plasmon damping and an unexpected generation...
Abstract Second harmonic generation (SHG) is a nonlinear optical response arising exclusively from broken inversion symmetry in the electric‐dipole limit. Recently, SHG has attracted widespread interest as versatile and noninvasive tool for characterization of crystal emerging ferroic or topological orders quantum materials. However, conventional far‐field optics unable to probe local at deep subwavelength scale. Here, near‐field imaging 2D semiconductors heterostructures with spatial...
When light-matter polaritons travel in periodic media, they acquire properties akin to Bloch quasi-particles crystals.
The design and performance of a cryogen-free low temperature scanning tunneling microscope (STM) housed in ultrahigh vacuum (UHV) are reported. was done by directly integrating Gifford-McMahon cycle cryocooler to Besocke-type STM, the vibration isolation achieved using two-stage rubber bellow between UHV-STM interface with helium exchange gas cooling. A base 15 K at STM achieved, possibility further decrease higher cooling power adding additional stage under interface. Atomically sharp...
Excitons in transition metal dichalcogenide monolayer have recently attracted great interest due to their extremely large binding energy, causing giant bandgap renormalization. In this work, we examined the screening effect of graphite and bilayer graphene on excitons molybdenum diselenide (MoSe2) grown by molecular beam epitaxy (MBE). Through combinational study scanning tunneling spectroscopy (STS) photoluminescence (PL) measurements, determined energy ~0.58 eV for MoSe2 both substrates at...
Recent developments of the scattering-type scanning near-field optical microscope at cryogenic temperatures (cryogenic s-SNOM or cryo-SNOM) have led to many breakthroughs in studies low energy excitations quantum materials. However, simultaneous demands on vibration isolation, base temperature, precise nano-positioning, and access make construction a cryo-SNOM daunting task. Adding overhead space required for is atomic force microscopy control, which predominantly utilizes laser-based...
Abstract Kagome vanadates A V 3 Sb 5 display unusual low-temperature electronic properties including charge density waves (CDW), whose microscopic origin remains unsettled. Recently, CDW order has been discovered in a new material ScV 6 Sn , providing an opportunity to explore whether the onset of leads properties. Here, we study this question using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM). The ARPES measurements show minimal changes structure...
Abstract Among the metal hydrides, Th 4 H 15 is first reported superconductor with a relatively high T c ≈ 8 K at ambient pressure. Here we report on synthesis and characterization of low- superconducting modification , which obtained via hydrogenating 5 GPa 800 °C by using ammonia borane as hydrogen source. Measurements resistivity, magnetic susceptibility, specific heat confirm that sample shows bulk transition 6 K, about 2 lower than previously. Various characteristic parameters have been...
Abstract Magnetic fields can have profound effects on the motion of electrons in quantum materials. Two-dimensional (2D) electron systems subject to strong magnetic are expected exhibit quantized Hall conductivity, chiral edge currents, and distinctive collective modes referred as magnetoplasmons magnetoexcitons. Generating these propagating charge-neutral samples imaging them at their native nanometer length scales thus far been experimentally elusive tasks. In this study, we visualize...
Terahertz (THz) absorbers based on the Salisbury screen have attracted significant attention for high absorption performance and simple structure. Graphene is suitable high-performance THz due to its extraordinary electronic optical properties. The study of graphene screens has great interest, where number layers significantly affects interface impedance matching efficiency. In this work, we proposed a sandwich-structured graphene/Polyimide (PI) /Au absorber screen. results show that peak...
Ultraclean graphene at charge neutrality hosts a quantum critical Dirac fluid of interacting electrons and holes. Interactions profoundly affect the dynamics graphene, which is encoded in properties its collective modes: surface plasmon polaritons (SPPs). The group velocity lifetime SPPs have direct correspondence with reactive dissipative parts tera-Hertz (THz) conductivity fluid. We succeeded tracking propagation over sub-micron distances femto-second (fs) time scales. Our experiments...
In this work we present a route for energy scaling in external pulse compression based on layered Kerr media combined with 1D focusing geometry. A highly stable 92%-efficient 4-fold of 1030-nm pulses is demonstrated.