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The ultrafast carrier dynamics of the multiferroic BiFeO3 film in a broad temperature range is investigated using optical pump-probe spectroscopy. The photoexcited electrons release their energy with optical phonons emission through electron-phonon coupling in about 1 ps. The following intermediate process is identified as dynamical spin-lattice coupling in several picoseconds. Furthermore, the peak values of the optical reflectivity and the time constants of carrier relaxation channels show significant changes while the temperature varies from 137.5K to around 195 K, this aligns with the previously reported hidden phase transition. Our study demonstrates that ultrafast spectroscopy is a sensitive method to look into the dynamical interactions among the on-site high-energy electrons accumulated in the p conduction band of Bi, coherent optical phonon, as well as the spin degree of freedom. These features play crucial roles in the characterization of phase transitions. [ABSTRACT FROM AUTHOR]

The article focuses on a study which identified novel chitinase-like proteins in the silkworm Bombyx mori genome. The study found nine chitinases and three hypothetical chitinases in the silkworm. It described the gene structure and chromosome location of Bombyx mori Chitinases, and the function of such chitinases. Study authors also analyzed the domain of Bombyx mori chitinases.

The operation of an all-optical magnetic switching based on the paramagnetic NaTb(WO4)2 crystals is carried out by the time-resolved magneto-optical Faraday effect. Our results demonstrate that the switching time can be as fast as ∼500 fs at room temperature. The switching amplitude shows a linear dependence on the excitation intensity, which is proportional to the magnetization induced by the circularly polarized light. Based on the inverse Faraday effect in magneto-optical crystal, the switching mechanisms arising from circular dichroism and birefringence are discussed. By tailoring the magneto-optical properties of NaTb(WO4)2 crystal, the switching magnitude can be modulated. [ABSTRACT FROM AUTHOR]

Excitation photon energy and carrier density dependence of spin dynamics in bulk CdTe crystal was studied by time resolved pump-probe reflectivity technique at room temperature. The results show that spin relaxation time decreases monotonously. While with increasing excitation carrier density, the time constants increases initially then decreases after reaching a maximum value. Our experimental results reveal that both D’yakonov–Perel’ [M. I. D’yakonov and V. I. Perel’, Sov. Phys. JETP 38, 177 (1974)] and Elliot–Yafet [R. J. Elliott, Phys. Rev. 96, 266 (1954); Y. Yafet, Solid State Phys. 14, 1 (1963)] mechanisms dominate the spin relaxation process in CdTe crystal. [ABSTRACT FROM AUTHOR]

Linear chains of SiO2-coated Au nanoparticles, exhibiting large third-order nonlinearity at multiple wavelengths ranging from visible to near infrared, were successfully synthesized and self-assembled on glass substrates using a reduction of HAuCl4 and chemical surfactant modification. The optical absorption spectra peaking at 530, 620, 715, 830, and 1100 nm wavelengths were measured to the transverse and longitudinal surface plasmon resonance modes of 2, 3, 4, and 5 Au particles, respectively. Greatly enhanced third-order nonlinear optical responses have been observed at multiple wavelengths. [ABSTRACT FROM AUTHOR]

One-dimensional photonic crystals (1D PC) with two CdS defect layers in a SiO2/TiO2 dielectric thin film stack were fabricated. Two-photon absorption (TPA) coefficients of the CdS defect layers in the 1D PC were investigated using femtosecond pump-probe method. Significant enhancement of the TPA coefficient in the CdS defect layers was observed to occur at the two defect modes. Experimental results show that the enhanced TPA coefficient at the defect mode of 800 nm is larger than that at the defect mode of 762 nm. A numerical simulation by matrix transfer method is performed and agrees with the experimental results very well. [ABSTRACT FROM AUTHOR]

From the commercial extract of the leaves of Stevia rebaudiana Bertoni, a minor steviol glycoside, 13-[(2-O-β-D-glucopyranosyl-3-O-β-D-glucopyranosyl-β-D-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid-[(2-O-(3-O-β-D-glucopyranosyl-α-L-rhamnopyranosyl)-3-O-β-D-glucopyranosyl-β-D-glucopyranosyl) ester] (1); also known as rebaudioside O having seven sugar units has been isolated. Its structural characterization has been achieved by the extensive 1D (1H and 13C), and 2D NMR (COSY, HMQC, HMBC) as well as mass spectral data. Further, hydrolysis studies were performed on rebaudioside O using acid and enzymatic methods to identify aglycone and sugar residues in its structure as well as their configurations.

We report the broadband emission of terahertz (THz) pulse in metallic patterned ferromagnetic heterostructures CoFeB/Pt based on inverse spin-Hall effect, by illuminating a train of linearly polarized 120-fs-wide laser pulses at 800 nm. The spatial-temporal distribution of charge currents by changing the length of the subwavelength rectangular metal blocks allows for not only effectively controlling the magnitude, but subtly tuning the center frequency and bandwidth of the emitted THz pulses. Our results will open new avenues for the study of modulated spintronic-based THz emitters. [ABSTRACT FROM AUTHOR]

Recently, ferromagnetic (FM) heterostructures have been demonstrated to emit THz radiation induced by femtosecond laser pulses. In such spintronic THz emitters, an in-plane external magnetic field is technological required to assist the orientations of the magnetization, which could be an obstacle for practical micro-electrooptic applications. Here, as a proof-of-concept, THz generation is based on the inverse spin Hall effect of the FM/Ta within a magnetic tunneling junction (MTJ) without external magnetic field. Furthermore, THz emission can be engineered by modulating of the tunneling conductivity within a photoexcited MTJ as the relative magnetizations of two FM layers change their alignments. [ABSTRACT FROM AUTHOR]

A dual-band plasmon induced transparency (DBPIT) metamaterial based on monolayer graphene in terahertz regime is designed and studied numerically. We demonstrated that both the resonance frequency and transmission amplitude of the structure can be independently tuned by manipulating the Fermi level of graphene via gate voltage. The terahertz transmission of the DBPIT can be well reproduced with a classical three-oscillator model. Furthermore, the transmission amplitude can be additionally enhanced due to the improved mode coupling originated from the magnetic near field enhancement enabled by the Diabolo-like structure. This work may open up a new avenue for designing multiple-band functional devices. [ABSTRACT FROM AUTHOR]

We report the broadband terahertz (THz) radiation in the metallic ferromagnetic (FM) heterostructures, upon irradiation of a femtosecond laser pulse at room temperature. The origin of THz generation from FM heterostructures can be interpreted using two terms: the transient demagnetization (a local modification of spin order of the FM metal) and electric-dipole radiation resulting from a non-local spin current pulses. Here, we show that the THz emission is dominated by the photo-excited transient charge current, which is converted from the spin current with inverse spin Hall effect. We tailor the metallic heterostructures with different non-magnetic thin layer (Pd or Ru) and FM materials (CoFeB or CoFe), to shape the THz transients. Moreover, we find that a saturation effect of THz radiation for CoFeB/Pd is less compared to CoFeB/Ru. THz emission spectroscopy can be used to qualitatively visualize the spin accumulation in the heterostructures. [ABSTRACT FROM AUTHOR]

Plants under pathogen attack produce high levels of ethylene, which plays important roles in plant immunity. Previously, we reported the involvement of ACS2 and ACS6, two Type I ACS isoforms, in Botrytis cinerea-induced ethylene biosynthesis and their regulation at the protein stability level by MPK3 and MPK6, two Arabidopsis pathogen-responsive mitogen-activated protein kinases (MAPKs). The residual ethylene induction in the acs2/acs6 double mutant suggests the involvement of additional ACS isoforms. It is also known that a subset of ACS genes, including ACS6, is transcriptionally induced in plants under stress or pathogen attack. However, the importance of ACS gene activation and the regulatory mechanism(s) are not clear. In this report, we demonstrate using genetic analysis that ACS7 and ACS11, two Type III ACS isoforms, and ACS8, a Type II ACS isoform, also contribute to the B. cinerea-induced ethylene production. In addition to post-translational regulation, transcriptional activation of the ACS genes also plays a critical role in sustaining high levels of ethylene induction. Interestingly, MPK3 and MPK6 not only control the stability of ACS2 and ACS6 proteins via direct protein phosphorylation but also regulate the expression of ACS2 and ACS6 genes. WRKY33, another MPK3/MPK6 substrate, is involved in the MPK3/MPK6-induced ACS2/ACS6 gene expression based on genetic analyses. Furthermore, chromatin-immunoprecipitation assay reveals the direct binding of WRKY33 to the W-boxes in the promoters of ACS2 and ACS6 genes in vivo, suggesting that WRKY33 is directly involved in the activation of ACS2 and ACS6 expression downstream of MPK3/MPK6 cascade in response to pathogen invasion. Regulation of ACS activity by MPK3/MPK6 at both transcriptional and protein stability levels plays a key role in determining the kinetics and magnitude of ethylene induction.

In this work, by using terahertz time-domain spectroscopy (THz-TDS), we investigate the temperature range of the SRT, and the resonant frequency and relaxation time of the THz spin waves in SmxDy1−xFeO3 single crystal. We show that the resonant frequency of the FM mode (measured at 40 K) increases linearly with the Sm dopant concentration within the range from x  =  0.5 to 0.7. The temperature- and dopant-induced changes of the magnetic anisotropy of Fe3+ ions are accessed by the resonant frequency shifts. Upon cooling, the lifetime of oscillations in the AFM mode increases exponentially and can be subtly tuned by varying the Sm dopant. These results lead to an improved understanding of dopant-tuned spin wave dynamics and magnetoanisotropy parameter in rare-earth orthoferrites. [ABSTRACT FROM AUTHOR]

The article offers the authors' insights concerning the comment given on their previous paper about carrier density and photon energy dependence of spin relaxation at room temperature in CdTe crystal. The authors emphasize that an additional mechanism exists, which contributes to the electron spin relaxation at higher carrier concentration. The authors note that D'yakonov-Perel (DP) mechanism based on kinetic spin Bloch equation (KSBE) model could well explain the nonmonotonous spin relaxation.

Spintronic heterostructures consisting of ferromagnetic (FM) and nonmagnetic (NM) have become increasingly important devices for terahertz (THz) pulse generation, named as spintronic THz emitter (STE). The recycling of the laser pump energy is known to have a key impact on further improvement of the THz emission. Here, an efficient and practical approach to enhance and manipulate THz generation based on a cascaded Pt/CoFe/Ta trilayer fabricated on a flexible polyethylene terephthalate (PET) substrate is shown. Considering the refractive index n of PET is ≈1.61 at 1.55 eV and ≈1.75 at THz frequencies, it is anticipated that the femtosecond (fs) laser pulse propagates with a similar group velocity as the generated THz pulse. Therefore, the cascaded design enables all THz emission from each PET/STE propagating almost in-phase and yields a 1.55 times amplification compared to a single PET/STE. Two proof-of-concept demonstrations are experimentally presented. First one, a metasurface can be assembled with the cascaded PET/STE to manipulate the THz signal. Second one, the cascaded PET/STE is used to perform a spectroscopic measurement of riboflavin. These demonstrations highlight the potential of flexible PET/STE for building blocks of advanced functionalities, such as compact THz emitters, THz spectroscopic, and imaging systems. [ABSTRACT FROM AUTHOR]

We report on the coherent control of terahertz (THz) spin waves in a canted antiferromagnet yttrium orthoferrite, YFeO3, associated with a quasiferromagnetic (quasi-FM) spin resonance at a frequency of 0.3 THz, using a single-incident THz pulse. The spin resonance is excited impulsively by the magnetic field component of the THz pulse. The intrinsic dielectric anisotropy of YFeO3 in the THz range allows for coherent control of both the amplitude and the phase of the excited spin wave. The coherent control is based on simultaneous generation of two interfering phase-shifted spin waves whose amplitudes and relative phase, dictated by the dielectric anisotropy of the YFeO3 crystal, can be controlled by varying the polarization of the incident THz pulse with respect to the crystal axes. The spatially anisotropic decay of the THz-excited FM spin resonance in YFeO3, leading to an increasingly linear polarization of the THz oscillation at the spin resonance frequency, suggests a key role of magnon-phonon coupling in spin-wave energy dissipation. [ABSTRACT FROM AUTHOR]

Based on FLUENT software, the VOF model was selected to numerically simulate the transfer behavior of ultrasonic-assisted MIG welding droplet under the effect of gravity, surface tension, electromagnetic force and plasma flow force. The influence of ultrasonic vibration on the necking radius of the plasma flow transfer of conventional MIG welding droplets is analyzed, and the effects of ultrasonic vibration transmission and radiation on the internal pressure, vector and the entire calculated flow field of the droplet are explored. The results of comparison with conventional MIG welding show that ultrasonic vibration causes rapid necking of droplet, the necking radius decreases and the plasma flow force increases, which promotes the transfer process of droplet; the internal dynamic pressure of the droplet increases and the absolute pressure in the flow field decreases. To verify the accuracy of the simulation results, welding tests were carried out, and the droplet transfer process was filmed by high-speed camera equipment and the droplet size was obtained by image processing method, so as to effectively and quantitatively verify the accuracy of the simulation results. The comparison results show that the simulation results are in good agreement with the experimental results, and the mathematical model of the droplet transfer is reasonable. [ABSTRACT FROM AUTHOR]

Electron spin dynamics in intrinsic bulk indium phosphide (InP) semiconductor is studied by time resolved pump probe reflectivity technique using the cocircularly and countercircularly polarized femtosecond pulses at room temperature and 70 K. The reflectivity change from bleaching into absorption is observed with increasing pump photon energy, which can be explained in terms of the spin sensitive band filling and band gap renormalization effects. Density dependence of electron spin relaxation time shows similar tendency at room temperature and 70 K. With increasing carrier density, the electron spin relaxation time increases and then decreases after reaching a maximum value. Our experimental results agree well with the recent theoretical prediction [Jiang and Wu, Phys. Rev. B 79, 125206 (2009)] and D'yakonov-Perel' mechanism is considered as a dominating contribution to the electron spin relaxation in intrinsic bulk InP semiconductor. [ABSTRACT FROM AUTHOR]

The article offers information on a study regarding enhancement of ferroelectric photovoltaic effect by polar order engineering. It mentions that ferroelectric materials for photovoltaics have sparked great interest because of their switchable photoelectric responses and above-bandgap photovoltages that violate conventional photovoltaic theory.

As a newly emergent type-II Dirac semimetal, platinum telluride (PtTe2) stands out from other two dimensional noble-transition-metal dichalcogenides for the unique band structure and novel physical properties, and has been studied extensively. However, the ultrafast response of low energy quasiparticle excitation in terahertz frequency remains nearly unexplored yet. Herein, we employ optical pump-terahertz probe (OPTP) spectroscopy to systematically study the photocarrier dynamics of PtTe2 thin films with varying pump fluence, temperature, and film thickness. Upon photoexcitation the terahertz photoconductivity (PC) of PtTe2 films shows abrupt increase initially, while the terahertz PC changes into negative value in a subpicosecond timescale, followed by a prolonged recovery process that lasted a few nanoseconds. The magnitude of both positive and negative terahertz PC response shows strongly pump fluence dependence. We assign the unusual negative terahertz PC to the formation of small polaron due to the strong electron-phonon (e-ph) coupling, which is further substantiated by temperature and film thickness dependent measurements. Moreover, our investigations give a subpicosecond timescale of simultaneous carrier cooling and polaron formation. The present study provides deep insights into the underlying dynamics evolution mechanisms of photocarrier in type-II Dirac semimetal upon photoexcitation, which is of crucial importance for designing PtTe2-based optoelectronic devices. [ABSTRACT FROM AUTHOR]