Thermoelectric and Topological Insulator Bismuth Chalcogenide Thin Films Grown Using Pulsed Laser Deposition

Bismuth chalcogenides have been intensively studied for their high-performance thermoelectric properties and their novel topological surface states, which could significantly benefit novel applications in fields such as TE devices, spintronics, and quantum computing. This chapter reports recent advances in pulsed laser deposition (PLD) for the growth of bismuth chalcogenide (e.g., Bi2Te3, Bi2Se3, and Bi3Se2Te) thin films and their novel properties. It covers a wide range of fields such as thin film growth using PLD for fabricating polycrystalline and epitaxial films with different thermoelectric, nanomechanical, and magnetotransport properties as a function of the PLD processing conditions. Moreover, the proximity-induced superconductivities in Bi inclusions/bismuth chalcogenide thin films are also reported and discussed in detail

Ultrafast Dynamics in Topological Insulators

Ultrafast dynamics of carriers and phonons in topological insulator Bi2Se3, CuxBi2Se3 (x = 0, 0.1, 0.125) single crystals were studied by time-resolved pump-probe spectroscopy. The coherent optical phonon (A1g1) is found via the damped oscillation in the transient reflectivity changes (∆R/R) for CuxBi2Se3. The observed red shift of A1g1 phonon frequency suggests the intercalation of Cu atoms between a pair of the quintuple layers of Bi2Se3 crystals. Moreover, the relaxation processes of Dirac fermion near the Dirac point of Bi2Se3 are studied by optical pump and mid-infrared probe spectroscopy through analyzing the negative peak of the ∆R/R. The Dirac fermion-phonon coupling strength was found in the range of 0.08–0.19 and the strength is reduced as it gets closer to the Dirac point. The ultrafast dynamics and fundamental parameters revealed by time-resolved pump-probe spectroscopy are important for designing the optoelectronics in the mid-IR and THz ranges

Nanostructuring Indium-Tin-Oxide Thin Films by Femtosecond Laser Processing

This chapter reviews the nanostructuring fabrications and properties of indium-tin-oxide (ITO) thin films by femtosecond laser annealing. Fundamental mechanisms of laser-induced periodic surface structures (LIPSS) and other nanostructures on ITO films are presented and discussed in detail. ITO films with large-area surface ripple structures with a multiperiodic spacing of ~800, ~400, and ~200 nm were successfully fabricated by femtosecond laser pulses, without scanning. The ITO films exhibited significant enhancement in electrical conductivity by ~30 times because of the formation and distribution of indium metal-like clusters. This metallic content of the laser-induced nanodots and nanolines further causes the anisotropic transmission characteristics in the visible range. In addition, by varying the laser fluences, nanostructures with cotton, brick, and ripple forms are generated on the surface of ITO films, which produce cyan, yellow, and orange colors. Intriguingly, the ITO films with laser-induced nanostructures can significantly attenuate blue light, thus they are potential for applications such as eye protection and information security

Exploring muonphilic ALPs at μ+μ−\mu^+\mu^- and μp\mu p colliders

Axion-like particles (ALPs) are new particles that extend beyond the standard model (SM) and are highly motivated. When considering ALPs within an effective field theory, their couplings with SM particles can be studied independently. It is a daunting task to search for GeV-scale ALPs coupled to muons in collider experiments because their coupling is proportional to the muon mass. However, a recent study by Altmannshofer, Dror, and Gori (2022) highlighted the importance of a four-point interaction, $W$-$\mu$-$\nu_{\mu}$-$a$, which coupling is not dependent on the muon mass. This interaction provides a new opportunity to explore muonphilic ALPs ($\mu$ALPs) at the GeV scale. We concentrate on $\mu$ALPs generated through this four-point interaction at future $\mu^+\mu^-$ and $\mu p$ colliders that subsequently decay into a pair of muons. This new channel for exploring $\mu$ALPs with $1$ GeV $\leq m_a\lesssim M_W$ can result in much stronger future constraints than the existing ones.Comment: 34 pages, 12 figures, 7 table

High-speed scanless entire bandwidth mid-infrared chemical imaging

Mid-infrared spectroscopy probes molecular vibrations to identify chemical species and functional groups. Therefore, mid-infrared hyperspectral imaging is one of the most powerful and promising candidates for chemical imaging using optical methods. Yet high-speed and entire bandwidth mid-infrared hyperspectral imaging has not been realized. Here we report a mid-infrared hyperspectral chemical imaging technique that uses chirped pulse upconversion of sub-cycle pulses at the image plane. This technique offers a lateral resolution of 15 $\mu$m, and the field of view is adjustable between 800 $\mu$m $\times$ 600 $\mu$m to 12 mm $\times$ 9 mm. The hyperspectral imaging produces a 640 $\times$ 480 pixel image in 8 s, which covers a spectral range of 640-3015 cm$^{-1}$, comprising 1069 wavelength points and offering a wavenumber resolution of 2.6-3.7 cm$^{-1}$. For discrete frequency mid-infrared imaging, the measurement speed reaches a frame rate of 5 kHz, the repetition rate of the laser. As a demonstration, we effectively identified and mapped different components in a microfluidic device, plant cell, and mouse embryo section. The great capacity and latent force of this technique in chemical imaging promise to be applied to many fields such as chemical analysis, biology, and medicine.Comment: 22 pages, 10 figure

BioRED: A Comprehensive Biomedical Relation Extraction Dataset

Automated relation extraction (RE) from biomedical literature is critical for many downstream text mining applications in both research and real-world settings. However, most existing benchmarking datasets for bio-medical RE only focus on relations of a single type (e.g., protein-protein interactions) at the sentence level, greatly limiting the development of RE systems in biomedicine. In this work, we first review commonly used named entity recognition (NER) and RE datasets. Then we present BioRED, a first-of-its-kind biomedical RE corpus with multiple entity types (e.g., gene/protein, disease, chemical) and relation pairs (e.g., gene-disease; chemical-chemical), on a set of 600 PubMed articles. Further, we label each relation as describing either a novel finding or previously known background knowledge, enabling automated algorithms to differentiate between novel and background information. We assess the utility of BioRED by benchmarking several existing state-of-the-art methods, including BERT-based models, on the NER and RE tasks. Our results show that while existing approaches can reach high performance on the NER task (F-score of 89.3%), there is much room for improvement for the RE task, especially when extracting novel relations (F-score of 47.7%). Our experiments also demonstrate that such a comprehensive dataset can successfully facilitate the development of more accurate, efficient, and robust RE systems for biomedicine

Understanding Multiferroic Hexagonal Manganites by Static and Ultrafast Optical Spectroscopy

Multiferroic hexagonal manganites ReMnO3 studied by optics are reviewed. Their electronic structures were revealed by static linear and nonlinear spectra. Two transitions located at ~1.7 eV and ~2.3 eV have been observed and attributed to the interband transitions from the lower-lying Mn3+dxy/dx2-y2 and dxz/dyz states to the Mn3+d3z2-r2 state, respectively. These so-called d-d transitions exhibit a blueshift as decreasing temperatures and an extra blueshift near TN. This dramatic change indicates that the magnetic ordering seriously influences the electronic structure. On the other hand, the ultrafast optical pump-probe spectroscopy has provided the important information on spin-charge coupling and spin-lattice coupling. Because of the strongly correlation between electronic structure and magnetic ordering, the amplitude of the initial rising component in ΔR/R shows striking changes at the vicinity of TN. Moreover, the coherent optical and acoustic phonons were observed on optical pump-probe spectroscopy. Both the amplitude and dephasing time of coherent phonons also exhibit significant changes at TN, which provide the evidence for spin-lattice interaction in these intriguing materials