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  • 1
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 69, No. 11 ( 2020), p. 117501-
    Abstract: With the discovery and development of topological materials, topological physics has attracted enormous research interest in the fields of contemporary condensed matter physics. Topological property, which describes such a property that physical quantity remains invariant under continuous transformation (such as Chern number), has been revealed in a variety of materials, including topological insulators, topological semimetals (such as Weyl or Dirac semimetals), topological magnetic materials, etc. One-dimensional chiral magnetic soliton, similar to magnetic skyrmion, is a type of magnetic configuration with topological origin and quasi-particle property, which has shown tremendous physical properties and device functionalities. In this review, we mainly focus on a chiral helimagnet, called Cr〈sub〉1/3〈/sub〉NbS〈sub〉2〈/sub〉, which possesses chiral magnetic soliton lattice and other more spin configurations under different conditions. We systematically summarize the work on Cr〈sub〉1/3〈/sub〉NbS〈sub〉2〈/sub〉, discussing its crystal symmetry, band structure, magnetic interactions, rich magnetic phases, and the physics of associated phase transitions. In particular, the layered crystal structure of Cr〈sub〉1/3〈/sub〉NbS〈sub〉2〈/sub〉 enables us to control the soliton number through tuning the layer number or crystal thickness. Our review provides a comprehensive summary of Cr〈sub〉1/3〈/sub〉NbS〈sub〉2〈/sub〉 in order to draw more attention to this interesting material. Moreover, we envision that our work could offer useful guidance to the researchers working on topological and chiral magnetic materials, and thus introducing topological or chiral magnetism into two-dimensional layered materials and promoting the development of modern magnetism and spintronics. Therefore, this review mainly focuses on a magnet, called Cr〈sub〉1/3〈/sub〉NbS〈sub〉2〈/sub〉. We systematically summarize the work on Cr〈sub〉1/3〈/sub〉NbS〈sub〉2〈/sub〉, discussing its crystal symmetry, band structure, magnetic interaction, rich magnetic phases and the interesting physical phenomena occurring at each phase transition. In addition, the layered crystal structure of Cr〈sub〉1/3〈/sub〉NbS〈sub〉2〈/sub〉 also enables us to use the layer number or crystal thickness to modulate and control its rich magnetic phases. We believe that our review provides a comprehensive summary of Cr〈sub〉1/3〈/sub〉NbS〈sub〉2〈/sub〉, which can make people have a better understanding of a typical topological magnetic material, thereby enriching the material types of magnets and low-dimensional material family and promoting the development of magnetism and spintronics applications, such as in magnetic memory devices, spintronic devices, and quantum information devices.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2020
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  • 2
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 71, No. 23 ( 2022), p. 237303-
    Abstract: The quasi-two-dimensional van der Waals intrinsic ferromagnetic semiconductor CrGeTe〈sub〉3〈/sub〉 possesses both a narrow semiconductor band gap and ferromagnetic properties, which makes it have a broad application prospect in the fields of spintronics and optoelectronics. In recent years, CrGeTe〈sub〉3〈/sub〉 has received extensive attention from researchers. To the best of our knowledge, so far, these studies have mainly focused on the optical response in near infrared and visible light range, but little has been done in THz frequency range. Therefore, it is upmost importance to obtain the complex dielectric constant as well as the photocarrier dynamics of the CrGeTe〈sub〉3〈/sub〉 at the THz frequency. Herewith, we use time-domain THz spectroscopy and time-resolved THz spectroscopy to investigate the fundamental properties of the CrGeTe〈sub〉3〈/sub〉 crystal in the THz range, including refractive index and absorption coefficient in THz frequency, as well as the THz photocarrier dynamics under 780-nm optical excitation. The fundamental characterizations are carried out on a 33-μm-thick CrGeTe〈sub〉3〈/sub〉 wafer by Fourier infrared spectroscopy, X-ray diffraction and Raman scattering. It is concluded that the CrGeTe〈sub〉3〈/sub〉 wafer shows an indirect band gap of 0.38 eV and good crystalline quality. The THz time domain spectroscopy presents that the CrGeTe〈sub〉3〈/sub〉 wafer has a refractive index and an absorption coefficient of 3.2 and 380 cm〈sup〉–1〈/sup〉, respectively, both of which show almost negligible dispersion in the investigated THz frequency. Under the optical excitation of 780 nm, the subsequent photocarrier relaxation can be well reproduced by a double exponential function: the fast relaxation shows a lifetime of 1–2 ps, depending on pump fluence, which is contributed by electron-phonon coupling; the slow relaxation has a typical lifetime of 7–8 ps, which is due to phonon-assisted electron-phonon recombination. The Pump fluence and delay time dependence of THz photoconductivity dispersion can be well fitted with Drude-Smith model, and the fitted results demonstrate that the plasma frequency increases with pump fluence in a fixed delay time, and then decreases with delay time increasing at a fixed pump fluence. The momentum scattering time shows that it decreases with pump fluence increasing, and increases with delay time increasing. These pump fluence and delay time dependent fitting microscopic parameters show similar tendencies to those of a conventional semiconductor. In a word, the experimental study here demonstrates that the narrow band-gap CrGeTe〈sub〉3〈/sub〉 wafer is well transparent and disperionless in a THz frequency range. From the above bandgap photoexcitation it follows that the wafer shows fast response and high modulation depth in THz radiation, providing a useful reference for the application of CrGeTe〈sub〉3〈/sub〉 in optoelectronics and related fields.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2022
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  • 3
    Online Resource
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    Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences ; 2022
    In:  Acta Physica Sinica Vol. 71, No. 23 ( 2022), p. 230501-
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 71, No. 23 ( 2022), p. 230501-
    Abstract: There is heterogeneity among different neurons, and the activities of neurons are greatly different, so the coupling between heterogeneous neurons can show richer dynamic phenomena, which is of great significance in understanding the neural function of the human brain. Unfortunately, in many studies of memristive coupled neurons, researchers have considered two adjacent identical neurons, but ignored the heterogeneous neurons. In this paper, two models are chosen, i.e. a Hindmarsh-Rose neuron model and a Hopfield neuron model, which are very different from each other. The proposed fractional-order linear memristor and fractional-order hyperbolic memristor simulated neural synapses are introduced into the two heterogeneous neuron models, considering not only the coupling between the two neurons, but also the coupling between single neurons. The self-coupling of neurons, a five-dimensional fractional memristive coupled heterogeneous neuron model, is established. In the numerical simulation of the new neuron model, the phase diagrams, bifurcation diagrams, Lyapunov exponent diagrams, and attraction basins are used to demonstrate the changes in coupling strength and other parameters in the memristive coupled heterogeneous neuron model, the new neuron model performance coexistence of different attractors. On the other hand, by changing the initial state of the system while keeping the relevant parameters of the system unchanged, the multistable phenomenon of the coupled heterogeneous neuron model can be observed. Using the phase diagram, the coexistence of different periods, and the phenomenon of period and chaos can be clearly observed. The coexistence of different attractor states can also be observed in the attractor basin. This has many potential implications for studying dynamic memory and information processing in neurons. Uncovering different types of multistable states from a dynamical perspective can provide an insight into the role of multistable states in brain information processing and cognitive function. Finally, the neuron model is implemented based on the micro control unit of the advanced RISC machine, and the phase diagram is observed under some parameters of the coupled neuron model on an oscilloscope. The experimental results show the validity of the theoretical analysis.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2022
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  • 4
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 70, No. 19 ( 2021), p. 195202-
    Abstract: Laser plasma interaction (LPI) is an important content in laser plasma related research, and it is one of the key issues related to the success or failure of inertial confinement fusion ignition, and has received extensive attention. In order to suppress the relevant LPI process as much as possible, the major laboratories around the world have developed a variety of beam smoothing methods through decades of research. However, the current understanding and suppression of LPI are still far from enough, and further in-depth studies are still needed. Generally, the research of LPI is based on nanosecond laser driving, and focuses mainly on the effects of the related LPI process caused by nanosecond lasers. However, the LPI processes, such as stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS), etc., occur and develop on a time scale of picoseconds.The comprehensive effect can be studied only on a longer scale of nanosecond. For highly nonlinear LPI processes, the comprehensive effect may be difficult to reflect the real physical laws. The emergence of the picosecond laser has made it possible to study the LPI process in more detail and on a more appropriate time scale. The present research tries to gain an understanding of LPI from a more refined perspective. The experimental research of picosecond laser driving LPI is carried out on the Shenguang-Ⅱ upgrade and picosecond laser facilities. First, a nanosecond laser is used to irradiate a target to generate a large-scale plasma, and a few nanoseconds later, the picosecond laser is injected as an interaction beam to drive the LPI scattering such as SBS and SRS. The spectral signal of backscatter light is measured experimentally by using the method of diffuse reflector. From the research results it is found that the backward signals of the band near the laser wavelength contain, in addition to the true backward SBS component, a large number of interference signals introduced by picosecond laser and nanosecond laser. The interference signal introduced by nanosecond laser can be eliminated by using specific measures, but the interference signal introduced by picosecond laser cannot be eliminated experimentally, which will affect the estimation of the true share of the backward SBS. The comprehensive results show that under different experimental conditions, the backward scatter energy of SBS may be less than half that of the total recorded signals. This result is helpful in further understanding and re-recognizing previous relevant experimental data.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2021
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  • 5
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 71, No. 21 ( 2022), p. 215201-
    Abstract: In order to verify that the large-scale low-density plasma has a significant gain effect on the quality of the ultra-hot electron beam in ultra-strong ultra-short pulse laser interactions with matter, on the Shenguang-II upgraded laser facility, we carry out an experimental study on the optimization of relativistic electron beams that combine long and short pulse lasers to generate large-scale low-density pre-plasma. A nanosecond laser is used to ablate the thin hydrocarbon film. After a period of time, a large-scale low-density plasma is formed. The second picosecond short pulse laser then interacts with the formed low-density plasma, and accelerates the electrons to the relativity magnitude. Through the comparative analysis between different experimental conditions in the experiment, it is found that the existence of large-scale low-density plasma significantly increases the intensity of the relativistic electron beam along the laser propagation direction. In the comparative test of three shooting methods (long and short pulse combined driving double-layer target, short pulse driving double-layer target, short pulse driving single-layer target), we find that the energy bands above 1 MeV can be produced by the long pulse and the short pulse jointly driving double-layer target. The gamma-ray intensity is nearly twice that of the other two schemes. In addition, we also find in the experiment that when the time interval between nanosecond-picosecond pulses changes, the pre-plasma electron density and density scale length of the CH film irradiated by the nanosecond laser will be different. When the time interval is 0 ns, the expansion of the plasma is still insufficient, and the density distribution of the pre-plasma is steep. Part of the picosecond laser energy will be reflected at the critical density surface. Insufficient absorption of picosecond laser energy reduces the generation of relativistic electrons.When the time interval is 1 ns, the plasma state is more appropriate. The picosecond laser will form a self-focusing plasma channel in the plasma, thereby efficiently depositing energy, breaking through the energy limit of ponderomotive force acceleration, and obtaining more higher energy relativistic electrons. When the time interval is longer, such as 1.5 ns or more, the plasma can be fully expanded, the electron density becoming too low. Most of the picosecond laser will pass through the pre-plasma, affecting energy deposition and failing to generate more relativistic electrons.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2022
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  • 6
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 68, No. 11 ( 2019), p. 110502-
    Abstract: In this paper, a new method of encrypting a color image based on 〈i〉θ〈/i〉 modulation is proposed by using the tricolor principle and computer-generated hologram (CGH) technology. The encryption process includes the 〈i〉θ〈/i〉-modulated three primary color components and the coding of computer-generated hologram, which is implemented in a Fresnel diffraction and spatial filtering system. Firstly, the color image modulated by the first random phase key is divided into three encryption channels by red laser, green laser, blue laser, and tricolor filters. Each channel is introduced by a transmissive amplitude-type sinusoidal grating with different directions, which is used to separate the three primary color components in the spatial spectrum plane. Secondly, the modulation results of tricolor components are superimposed together to form a compound image, and the phase truncation of the superposition result is performed to achieve the asymmetric encryption. Finally, the amplitude of the compound image is modulated by the second random phase key and is encoded into a binary real-value gray-color CGH by Roman-type coding method. Therefore, the gray-color information of the original image is completely hidden in the encrypted CGH, which is more general and deceptive in the storage and transmission process. Decryption is an inverse process of the encryption. Firstly, the encrypted CGH is placed on the input plane of the spatial filtering and Fresnel diffraction system. Secondly, the demodulation of CGH phase key and the spatial filtering based on optical filter are performed. Finally, the color plaintext image is obtained by using the correct Fresnel diffraction. The simulation results show the validity and feasibility of the proposed method. In addition, the anti-noise attack and anti-shearing attack performance of this color image encryption method are investigated. Compared with results from the three presented methods reported in the literature, our investigated results demonstrate that this method has good robustness to noise attack and shearing attack, and has obvious advantages when the attack noise density is larger. Due to the characteristics of high security and anti-noise, we believe that this color image encryption method promises to have important applications in the information transmission and multi-user authentication.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2019
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  • 7
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 70, No. 12 ( 2021), p. 127801-
    Abstract: Two-dimensional (2D) materials represented by graphene and molybdenum disulfide (MoS〈sub〉2〈/sub〉) have attracted much attention in recent years due to their advantages in electrical, thermal, optical and mechanical properties. As a branch of 2D materials, 2D magnetic materials have special properties such as magnetic anisotropy and single-layer magnetic order. Especially, their magnetism can also be controlled by a variety of physical fields, and it possesses various physical properties and potential applications. Therefore, they have received widespread attention of researchers gradually. In this article, we summarize the types, synthesis methods, basic characteristics and characterization methods of 2D magnetic materials in detail, and the magnetism controlling of 2D magnetic materials as well. Finally, a simple outlook on the research directions and future challenges of 2D magnetic materials is given.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2021
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