A5001384071- Topological Materials and Phenomena
- Terahertz technology and applications
- Spectroscopy and Laser Applications
- Quantum Mechanics and Non-Hermitian Physics
- Advanced Semiconductor Detectors and Materials
- Quantum Dots Synthesis And Properties
- Chalcogenide Semiconductor Thin Films
- Spectroscopy and Quantum Chemical Studies
- Semiconductor Quantum Structures and Devices
- Laser-Matter Interactions and Applications
- Metamaterials and Metasurfaces Applications
- Surface Modification and Superhydrophobicity
- Orbital Angular Momentum in Optics
- 2D Materials and Applications
- Laser Material Processing Techniques
- Physics of Superconductivity and Magnetism
- Spectroscopy Techniques in Biomedical and Chemical Research
- Graphene research and applications
- Near-Field Optical Microscopy
- Superconducting and THz Device Technology
- Quantum many-body systems
- Laser-Ablation Synthesis of Nanoparticles
- Bach Studies and Logistics Development
- Synthesis and properties of polymers
- Nanomaterials and Printing Technologies
Nordic Institute for Theoretical Physics
2024
National Cheng Kung University
2024
National Yang Ming Chiao Tung University
2013-2023
National Synchrotron Radiation Research Center
2020-2023
The recent focus on topological insulators is due to the scientific interest in new state of quantum matter as well technology potential for a generation THz optoelectronics, spintronics and computations. It important elucidate dynamics Dirac fermions topologically protected surface state. Hence we utilized novel ultrafast optical pump mid-infrared probe explore near point. femtosecond snapshots relaxation process were revealed by optics. Specifically, fermion-phonon coupling strength cone...
THz radiation is generated from topological insulators using femtosecond laser pulses. Two-channel free carrier absorption with bulk and surface carriers indispensable to explaining the strong dependence of emission power on concentration. The characteristics provide valuable information regarding fundamental properties Dirac fermions. Three-dimensional (TIs) are characterized by a narrow bandgap in cone-like conducting state.1-3 state new quantum matter caused spin–orbit interaction...
Platinum diselenide (PtSe2) is a group-10 two-dimensional (2D) transition metal dichalcogenide that exhibits the most prominent atomic-layer-dependent electronic behavior of "semiconductor-to-semimetal" when going from monolayer to bulk form. This work demonstrates an efficient photoelectrochemical (PEC) conversion for direct solar-to-hydrogen (H2) production based on 2D layered PtSe2/Si heterojunction photocathodes. By systematically controlling number atomic layers wafer-scale PtSe2 films...
Abstract Topological insulators (TIs) are interesting quantum matters that have a narrow bandgap for bulk and Dirac-cone-like conducting surface state (SS). The recent discovered second Dirac (SS) bands (BBs) located ~1.5 eV above the first SS important optical coupling in TIs. Here, we report on time-domain measurements of THz radiation generated from TIs n-type Cu 0.02 Bi 2 Se 3 p-type Te single crystals by ultrafast pulse excitation. observed polarity-reversal originated transient current...
In this study, we carried out 800-nm pump and ultra-broadband mid-infrared (MIR) probe spectroscopy with high time-resolution (70 fs) in bulk Ge. By fitting the time-resolved difference reflection spectra [ΔR(ω)/R(ω)] Drude model 200-5000 cm-1 region, time-dependent plasma frequency scattering rate have been obtained. Through calculation, can further get photoexcited carrier concentration mobility. The Auger recombination essentially dominates fast relaxation of carriers within 100 ps...
Abstract We design and demonstrate a flexible, ultrathin double-sided metamaterial perfect absorber (MPA) at 2.39 terahertz (THz), which enables excellent light absorbance under incidences from two opposite sides. Herein, the MPA is fabricated on λ 0 /10.1-thick flexible polyethylene terephthalate substrate of ε r = 2.75 × (1 + 0.12 i ), sandwiched by identical randomized metallic patterns our stochastic process. Such an provides tailored permittivity permeability to approach impedance free...
Ultrafast dynamics in molecules, nanostructures, and interfaces are commonly studied using pump-probe spectroscopy. The bandwidth for this approach has been limited to about 1000 cm${}^{-1}$ the midinfrared region. authors develop an upconversion technique femtosecond-scale detection, demonstrate ultrabroadband system with a spectral range of 200---5000 cm${}^{-1}$. Their dramatically improves access energy regions interest investigating relaxation optically excited systems as diverse...
A novel approach for the production of both amorphous and crystalline selenium nanoparticles (SeNPs) using femtosecond laser-induced plasma shock wave on surface Bi2Se3 topological insulators at room temperature ambient pressure is demonstrated. The shape size SeNPs can be reliably controlled via kinetic energy obtained from laser pulses, so these are applicable as active components in nanoscale applications. Importantly, rapid, low-cost eco-friendly synthesis strategy developed this study...
This study presents the design and fabrication of a vertically stacked aluminum (Al) nanosquare metasurface for infrared cutoff (IR-cut) applications, utilizing advanced nanomaterials to enhance device performance by blocking light while maintaining transparency in visible spectrum. Rigorous coupled wave analysis simulations were employed evaluate optimize optical metasurface, focusing on key parameters such as size, period, thickness, gap between layers. The optimized design, based...
We propose an approach to use linearly polarized light imprint superconducting vortices. Within the framework of generalized time-dependent Ginzburg-Landau equations we demonstrate induction coherent vortex pairs that are moving in phase with electormagnetic wave oscillations. The overall vorticity superconductor remain zero throughout cycle. Our results uncover rich multiscale dynamics SC and suggest new optical applications for various types structured light. In departure from classical...
We investigate the effects of a Laguerre-Gaussian (LG) beam on superconducting state. show that vortex angular momentum LG affects state and induces currents. The induction current by microwave radiation is illustrated Josephson loop SQUID devices. In particular, we establish coupling dc to ac magnetic flux can stabilize <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mi>π</a:mi></a:math> phase in SQUID. This happen via developing global or local minimum effective potential at...
We introduce a systematic approach that enables two robust methods for performing terahertz time-domain spectroscopy in reflection geometry. Using the Kramers-Kronig relations connection to accurate experimental measurements of amplitude electric field, we show how correct phase same field can be retrieved, even case partly misaligned measurements. Our technique allows accurately estimate optical properties principle any material reflects radiation. demonstrate accuracy our by extracting...
We developed a phase correction method for broadband terahertz time-domain spectroscopy in reflection geometry, which allows us to obtain quantitative and accurate values the complex refractive index of materials. The process is analytical, based on Kramers-Kronig relations, does not require any computationally intensive algorithms. validate it by extracting silicon, obtaining nominal value with an accuracy better than 2.5\% over 0.25--3.5 THz range, 0.6\% 1--2 range. use experimentally...
We investigate the effects of a Laguerre-Gaussian (LG) beam on superconducting state. show that vortex angular momentum LG affects state and induces currents. The induction current by light is illustrated Josephson loop SQUID devices. In particular, we establish coupling dc to AC magnetic flux can stabilize pi phase in SQUID. This happen via developing global or local minimum effective potential at pi. latter case, this happens Kapitza mechanism.
Challenge to control the quantum states of matter via light have been at forefront modern research on driven matter. We explore imprinting effects structured superconductors, demonstrating how numbers light-specifically spin angular momentum, orbital and radial order-can be transferred superconducting order parameter vortex dynamics. Using Laguerre-Gaussian beams, we show that by tuning amplitude electric field, it is possible manipulate a variety behaviors, including breathing pairs,...
We utilized a ultrafast optical pump mid-infrared probe to explore the dynamics of Dirac fermions near point in topological insulator. The femtosecond snapshots relaxation process were revealed by optics.
Time-resolved angle-resolved photoemission spectroscopy (Tr-APRES) gives direct insight into electron dynamics by providing temporal-, energy-, and momentum-resolved information in one experiment. A major obstacle to using high harmonic generation (HHG) probe pulses for is the low conversion efficiency, that is, flux of photons. We use a Yb-KGW based duo-laser source with an oscillator pump two separate amplifiers generate synchronized pulsed laser sources average energies 7.5 6 W. By...
Abstract Mid-infrared (MIR) light sources have much potential in the study of Dirac-fermions (DFs) graphene and topological insulators (TIs) because they a low photon energy. However, surface state transitions (SSTs) Dirac cones are veiled by free carrier absorption (FCA) with same spectral line shape that is always seen static MIR spectra. Therefore, it difficult to distinguish SST from FCA, especially TIs. Here, we disclose abnormal spectrum feature transient reflectivity changes (Δ R / )...
This study shows that a terahertz (THz) wave can be generated from the (001) surface of cleaved Bi$_{\textrm{2}}$Se$_{\textrm{3}}$ and Cu-doped single crystals using 800 nm femtosecond pulses. The THz power is strongly dependent on carrier concentration crystals. An examination dependence reveals two-channel free absorption to which Dirac fermions are indispensable. in significantly better absorbers radiation than bulk carriers at room temperature. Moreover, characteristics emission confirm...