Combining electron microscopy with atomic-scale calculations—A personal perspectivePantelides, Sokrates T.
doi: 10.1088/1674-1056/ad8ecepmid: N/A
I had the privilege and the pleasure to work closely with Stephen J. Pennycook for about twenty years, having a group of post-docs and Vanderbilt-University graduate students embedded in his electron microscopy group at Oak Ridge National Laboratory, spending on average a day per week there. We combined atomic-resolution imaging of materials, electron-energy-loss spectroscopy, and density-functional-theory calculations to explore and elucidate diverse materials phenomena, often resolving long-standing issues. This paper is a personal perspective of that journey, highlighting a few examples to illustrate the power of combining theory and microscopy and closing with an assessment of future prospects.
Strain-modulated antiferromagnetic Chern insulator in NiOsCl6 monolayerWu, Bin; Li, Na; Chen, Xin-Lian; Ji, Wei-Xiao; Wang, Pei-Ji; Zhang, Shu-Feng; Zhang, Chang-Wen
doi: 10.1088/1674-1056/ad84cbpmid: N/A
Recently, Chern insulators in an antiferromagnetic (AFM) phase have been suggested theoretically and predicted in a few materials. However, the experimental observation of two-dimensional (2D) AFM quantum anomalous Hall effect is still a challenge to date. In this work, we propose that an AFM Chern insulator can be realized in a 2D monolayer of NiOsCl6 modulated by a compressive strain. Strain modulation is accessible experimentally and used widely in predicting and tuning topological nontrivial phases. With first-principles calculations, we have investigated the structural, magnetic, and electronic properties of NiOsCl6. Its stability has been confirmed through molecular dynamical simulations, elasticity constant, and phonon spectrum. It has a collinear AFM order, with opposite magnetic moments of 1.3 μB on each Ni/Os atom, respectively, and the Néel temperature is estimated to be 93 K. In the absence of strain, it functions as an AFM insulator with a direct gap with spin–orbital coupling included. Compressive strain will induce a transition from a normal insulator to a Chern insulator characterized by a Chern number C = 1, with a band gap of about 30 meV. This transition is accompanied by a structural distortion. Remarkably, the Chern insulator phase persists within the 3%–10% compressive strain range, offering an alternative platform for the utilization of AFM materials in spintronic devices.
Analysis and measurement of vibration characteristics of a hollowing defect based on a laser self-mixing interferometerChen, Yu-Xin; Chen, Jin-Bo; Cao, Peng; Zhao, You-Guang; Wang, Jun; Teng, Xu-Wei; Wang, Chi
doi: 10.1088/1674-1056/ad7e99pmid: N/A
To solve the problems with the existing methods for detecting hollowing defects, such as inconvenient operation, low efficiency and intense subjectivity, and to improve the efficiency of the acoustic-optic fusion method for detecting hollowing defects, in this paper the vibration characteristics of hollowing defects are measured and analyzed using a laser self-mixing interferometer. The ceramic tile above the hollowing defect is equivalent to a thin circular plate with peripheral fixed support. According to Kirchhoff’s classical circular plate theory and the circular plate displacement function based on the improved Fourier series, a theoretical model of a circular plate is established. By solving the characteristic equation, the theoretical modal parameters of hollowing defects are obtained. Subsequently, an experimental system based on a laser self-mixing interferometer is built, and modal experiments are carried out using the hammering method. The experimental modal parameters are obtained with a professional modal analysis software. Through comparative analysis between the theoretical and experimental modal parameters, the error of the natural frequency results is found to be tiny and the mode shapes are consistent. These results provide theoretical guidance for a practical non-destructive acoustic-optic fusion method for detecting hollowing defects.
Influences of short-term and long-term plasticity of memristive synapse on firing activity of neuronal networkLi, Zhi-Jun; Zhang, Jing
doi: 10.1088/1674-1056/ad84c5pmid: N/A
Synaptic plasticity can greatly affect the firing behavior of neural networks, and it specifically refers to changes in the strength, morphology, and function of synaptic connections. In this paper, a novel memristor model, which can be configured as a volatile and nonvolatile memristor by adjusting its internal parameter, is proposed to mimic the short-term and long-term synaptic plasticity. Then, a bi-neuron network model, with the proposed memristor serving as a coupling synapse and the external electromagnetic radiation being emulated by the flux-controlled memristors, is established to elucidate the effects of short-term and long-term synaptic plasticity on firing activity of the neuron network. The resultant seven-dimensional (7D) neuron network has no equilibrium point and its hidden dynamical behavior is revealed by phase diagram, time series, bifurcation diagram, Lyapunov exponent spectrum, and two-dimensional (2D) dynamic map. Our results show the short-term and long-term plasticity can induce different bifurcation scenarios when the coupling strength increases. In addition, memristor synaptic plasticity has a great influence on the distribution of firing patterns in the parameter space. More interestingly, when exploring the synchronous firing behavior of two neurons, the two neurons can gradually achieve phase synchronization as the coupling strength increases along the opposite directions under two different memory attributes. Finally, a microcontroller-based hardware system is implemented to verify the numerical simulation results.
Optical image watermarking based on orbital angular momentum holographyZhu, Jialong; Ji, Jiaying; Wang, Le; Zhao, Shengmei
doi: 10.1088/1674-1056/ad8cbdpmid: N/A
We propose an optical image watermarking scheme based on orbital angular momentum (OAM) holography. Multiple topological charges (TCs, l) of OAM, as multiple cryptographic sub-keys, are embedded into the host image along with the watermark information. Moreover, the Arnold transformation is employed to further enhance the security and the scrambling time (m) is also served as another cryptographic key. The watermark image is embedded into the host image by using the discrete wavelet transformation (DWT) and singular value decomposition (SVD) methods. Importantly, the interference image is utilized to further enhance security. The imperceptibility of our proposed method is analyzed by using the peak signal-to-noise ratio (PSNR) and the histogram of the watermarked host image. To demonstrate robustness, a series of attack tests, including Gaussian noise, Poisson noise, salt-and-pepper noise, JPEG compression, Gaussian low-pass filtering, cropping, and rotation, are conducted. The experimental results show that our proposed method has advanced security, imperceptibility, and robustness, making it a promising option for optical image watermarking applications.
Coexisting and multiple scroll attractors in a Hopfield neural network with a controlled memristorMa, Qing-Qing; Lu, An-Jiang; Huang, Zhi
doi: 10.1088/1674-1056/ad8148pmid: N/A
A method of generating multi-double scroll attractors is proposed based on the memristor Hopfield neural network (HNN) under pulse control. First, the original hyperbolic-type memristor is added to the neural network mathematical model, and the influence of this memristor on the dynamic behavior of the new HNN is analyzed. The numerical results show that after adding the memristor, the abundant dynamic behaviors such as chaos coexistence, period coexistence and chaos period coexistence can be observed when the initial value of the system is changed. Then the logic pulse is added to the external memristor. It is found that the equilibrium point of the HNN can multiply and generate multi-double scroll attractors after the pulse stimulation. When the number of logical pulses is changed, the number of multi-double scroll attractors will also change, so that the pulse can control the generation of multi-double scroll attractors. Finally, the HNN circuit under pulsed stimulation was realized by circuit simulation, and the results verified the correctness of the numerical results.
Exact quantum dynamics for two-level systems with time-dependent drivingHe, Zhi-Cheng; Wu, Yi-Xuan; Xue, Zheng-Yuan
doi: 10.1088/1674-1056/ad8a4cpmid: N/A
It is well known that the time-dependent Schrrödinger equation can only be solved exactly in very rare cases, even for two-level quantum systems. Thus, finding the exact quantum dynamics under a time-dependent Hamiltonian is not only fundamentally important in quantum physics but also facilitates active quantum manipulations for quantum information processing. In this work, we present a method for generating nearly infinite analytically assisted solutions to the Schrödinger equation for a qubit under time-dependent driving. These analytically assisted solutions feature free parameters with only boundary restrictions, making them applicable in a variety of precise quantum manipulations. Due to the general form of the time-dependent Hamiltonian in our approach, it can be readily implemented in various experimental setups involving qubits. Consequently, our scheme offers new solutions to the Schrödinger equation, providing an alternative analytical framework for precise control over qubits.
Nonlinear enhanced mass sensor based on optomechanical systemMan, Xin-Xin; Sun, Jing; Zhang, Wen-Zhao; Luo, Lijuan; Jin, Guangri
doi: 10.1088/1674-1056/ad84cfpmid: N/A
A high-precision and tunable mass detection scheme based on a double-oscillator optomechanical system is proposed. By designating one of the oscillators as the detection port, tiny mass signals can be probed through the frequency shift of the output spectrum, utilizing the system’s optomechanically induced transparency (OMIT) effect. By solving the output of the optical mode, we demonstrate that the system exhibits two OMIT windows due to the double-oscillator coupling, with one window being strongly dependent on the mass to be detected. Characterizing the spectrum around this window enables high magnification and precise detection of the input signal under nonlinear parameter conditions. Additionally, our scheme shows resilience to environmental temperature variations and drive strength perturbations.