Abstract
Understanding the interaction between intense terahertz (THz) electromagnetic fields and spin systems has been gaining importance in modern spintronics research as a unique pathway to ...realize ultrafast macroscopic magnetization control. In this work, we used intense THz pulses with pulse energies in the order of 10 mJ/pulse generated from the terahertz free electron laser (THz-FEL) to irradiate the ferromagnetic domains of ErFeO
3
single crystal. It was found that the domain shape can be locally reconfigured by irradiating the THz − FEL pulses near the domain boundary. Observed domain reconfiguration mechanism can be phenomenologically understood by the combination of depinning effect and the entropic force due to local thermal gradient exerted by terahertz irradiation. Our finding opens up a new possibility of realizing thermal-spin effects at THz frequency ranges by using THz-FEL pulses.
Abstract
Energetic correlations and their dynamics govern the fundamental properties of condensed matter materials. Ultrafast multidimensional spectroscopy in the mid infrared is an advanced ...technique to study such coherent low-energy dynamics. The intrinsic many-body phenomena in functional solid-state materials, in particular few-layer samples, remain widely unexplored to this date, because complex and weak sample responses demand versatile and sensitive detection. Here, we present a novel setup for ultrafast multidimensional spectroscopy with noncollinear geometry and complete field resolution in the 15–40 THz range. Electric fields up to few-100 kV cm
−1
drive coherent dynamics in a perturbative regime, and an advanced modulation scheme allows to detect nonlinear signals down to a few tens of V cm
−1
entirely background-free with high sensitivity and full control over the geometric phase-matching conditions. Our system aims at the investigation of correlations and many-body interactions in condensed matter systems at low energy. Benchmark measurements on bulk indium antimonide reveal a strong six-wave mixing signal and map ultra-fast changes of the band structure with access to amplitude and phase information. Our results pave the way towards the investigation of functional thin film materials and few-layer samples.
The control of magnetic domain in correlated spin systems by optical pulses has been gaining importance in spintronics and related fields. In particular, ultrafast control of magnetic domain is one ...of the top areas of interest. Herein we demonstrate the magnetic domain control in ErFeO 3 single crystal, a weak ferromagnet, induced by high-intensity terahertz (THz) pulse excitation from a free-electron laser. THz pulses with a central frequency of 4 THz and pulse energy in the order of 10 mJ were used. The microscopic images of the magnetic domain inversion induced by the THz irradiation were recorded by the Faraday-rotation method using a He-Ne probe laser. The experimental results of the THz pulse irradiation at room temperature and at low temperature around the spin reorientation phase transition are presented. We show that the THz pulse excitation can expand the minor magnetic domain toward the direction of the THz beam spot. The magnetic domain inversion is caused by the combination of depinning of the magnetic domain due to local heating and the entropic force owing to the thermal gradient induced by THz irradiation.
We propose a hologram calculation technique that enables reconstructing a shaded three-dimensional (3D) image. The amplitude distributions of zone plates, which generate the object points that ...constitute a 3D object, were two-dimensionally modulated. Two-dimensional (2D) amplitude modulation was determined on the basis of the Phong reflection model developed for computer graphics, which considers the specular, diffuse, and ambient reflection light components. The 2D amplitude modulation added variable and constant modulations: the former controlled the specular light component and the latter controlled the diffuse and ambient components. The proposed calculation technique was experimentally verified. The reconstructed image showed specular reflection that varied depending on the viewing position.
SUMMARY
Plant ‘activators’, such as benzothiadiazole (BTH), protect plants from various diseases by priming the plant salicylic acid (SA) signalling pathway. We have reported previously that a ...transcription factor identified in rice, WRKY45 (OsWRKY45), plays a pivotal role in BTH‐induced disease resistance by mediating SA signalling. Here, we report further functional characterization of WRKY45. Different plant activators vary in their action points, either downstream (BTH and tiadinil) or upstream (probenazole) of SA. Rice resistance to Magnaporthe grisea, induced by both types of plant activator, was markedly reduced in WRKY45‐knockdown (WRKY45‐kd) rice, indicating a universal role for WRKY45 in chemical‐induced resistance. Fungal invasion into rice cells was blocked at most attempted invasion sites (pre‐invasive defence) in WRKY45‐overexpressing (WRKY45‐ox) rice. Hydrogen peroxide accumulated within the cell wall underneath invading fungus appressoria or between the cell wall and the cytoplasm, implying a possible role for H2O2 in pre‐invasive defence. Moreover, a hypersensitive reaction‐like reaction was observed in rice cells, in which fungal growth was inhibited after invasion (post‐invasive defence). The two levels of defence mechanism appear to correspond to Type I and II nonhost resistances. The leaf blast resistance of WRKY45‐ox rice plants was much higher than that of other known blast‐resistant varieties. WRKY45‐ox plants also showed strong panicle blast resistance. BTH‐induced resistance to Xanthomonas oryzae pv. oryzae was compromised in WRKY45‐kd rice, whereas WRKY45‐ox plants were highly resistant to this pathogen. However, WRKY45‐ox plants were susceptible to Rhizoctonia solani. These results indicate the versatility and limitations of the application of this gene.
Abstract
Intense terahertz pulses offer unique pathway to resonantly drive the correlated spin systems up to the nonlinear regime. However, detection of such nonlinear spin dynamics often suffers ...from the small signal amplitude that can be easily hindered by the linear background components. In order to efficiently extract the nonlinear signals, here we demonstrate that magnetooptical effect can be utilized. We excite spin precession in orthoferrite YFeO
3
by the magnetic field of intense terahertz pulse and probe its dynamics by transient transmissivity change in the near infrared. The observed waveforms contain quasi-ferromagnetic-mode magnon oscillation and its second harmonics with a comparably strong amplitude. The result can be explained by dielectric function derived from magnetorefractive Hamiltonian. We reveal that the strong second harmonic signal microscopically originates from the dynamics of the quasi-ferromagnetic mode magnon at nonlinear regime, wherein spin canting angle periodically oscillates.
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