In the realm of condensed matter physics, the properties of material are largely determined by the degrees of freedom associated with lattice, charge, orbital, and spin, as well as their intricate interplay. Unveiling the coupling mechanisms between these freedoms and effectively manipulating them necessitate a profound exploration into ultrafast dynamics, owing to the nanoseconds, femtoseconds, and even attoseconds timescales governing these fundamental interactions. Ultrafast transmission electron microscopy (UTEM) emerges as a powerful technique enabling the research of ultrafast dynamics with exceptional spatial-temporal resolution, showcasing diverse applications within nanoscale systems. Over the past decades, UTEM has witnessed significant advancements in instrument development, fostering its widespread utilization across various domains. This review firstly introduces the fundamental principles of UTEM and traces its historical evolution, intricately involving the integration of the pump-probe principle with transmission electron microscopy. Subsequently, the key performance characteristics of UTEM are succinctly summarized. Moreover, a detailed exposition is provided on the manifold applications of UTEM, encompassing structural dynamics, magnetic phenomena, and near-field optics, each delineated according to their respective time-resolved methodologies. Concluding the review, a forward-looking perspective on the UTEM technique is presented, envisioning its significance in the realm of ultra-fast dynamics research. UTEM
Erbium-doped crystals are promising candidates for fiber-compatible quantum memories due to their optical transition in the telecommunication C-band. Here, we investigate the optical decoherence dynamics of isotopically enriched Er-167(3+):Y2SiO5: (YSO) at sub-Kelvin temperatures and low magnetic fields (<1 T). We observed an optical homogeneous linwidth of 100 Hz at 100 mK and 0.2 T-significantly narrower than previous values obtained at 7 T in a sample with the same Er-167(3+) concentration. We analyze the dependence of coherence properties on magnetic field orientation and temperature, identifying spectral diffusion resulted from the host spin bath as key decoherence mechanisms. We further identified that superhyperfine interactions between the Er-167(3+) and the host bath spins pose challenges for long-term storage protocols requiring precise spectral tailoring. To address this issue, we propose a strategy that combined the Stark modulation memory scheme with noiseless photon echo storage protocol, which is expected to achieve spin-wave quantum storage with lower noise and higher efficiency.
The discovery of superconductivity in infinite-layer nickelate films marks a groundbreaking addition to the family of unconventional superconductors, providing new insights into mechanism of unconventional high temperature superconductivity. However, synthesizing these superconducting nickelates presents significant challenges: they cannot be grown directly and instead require a two-step synthesis protocol involving initial deposition of a perovskite precursor phase (e.g., Nd0.8Sr0.2NiO3) followed by topotactic reduction to the infinite-layer structure (Nd0.8Sr0.2NiO2). This process is further complicated by the extreme sensitivity of both steps to synthesis conditions, necessitating stringent control over the crystallinity and stoichiometry of the parent phase. In this study, we uncover nickel deficiency during pulsed laser deposition (PLD) of the parent-phase Nd0.8Sr0.2NiO3. By incorporating 15% excess nickel into the PLD target, we mitigate this loss, suppress secondary phase formation in the Nd0.8Sr0.2NiO3 parent film, and ultimately obtain a phase-pure Nd0.8Sr0.2NiO2 film exhibiting superconductivity after following reduction. Notably, we observe a doping-dependent insulator-to-superconductor transition in films synthesized from targets with varying nickel content after reduction. X-ray photoelectron spectroscopy (XPS) confirms that the Nd/Ni ratio in films derived from nickel-over-doped targets (15% excess) aligns closely with the ideal stoichiometry. These findings underscore the indispensable role of stoichiometric precision in stabilizing infinite-layer nickelates and establish a practical synthesis strategy for optimizing their superconducting performance.
Owing to the formal analogy between their governing equations, concepts from electromagnetic wave physics have been successfully extended to water-wave systems. Here, we propose and experimentally demonstrate the water-wave metagratings (WMGs) capable of wavefront modulation based on the generalized Snell's law. These WMGs generate anomalous diffraction, including both retroreflection and negative refraction, by engineering the integer parity of supercells. As a proof of concept, we realize broadband water-wave focusing using WMGs. This work opens new avenues for compact and tunable water-wave devices, with potential applications in wave-energy harvesting and marine engineering.
To address the critical challenges of insufficient light-matter interaction, high noise, and poor integration in traditional terahertz detectors, this paper proposes a laser-enhanced terahertz detector based on a 3D microstructure. The detector utilizes room-temperature Weyl semimetal MoWTe2 as the active layer and achieves monolithic integration on a silicon substrate, with core innovations including: (i) employing MoWTe2 as the active layer to enable efficient terahertz absorption and high carrier mobility at room temperature, eliminating the need for cryogenic cooling; (ii) fabricating a 3D rotating rectangular array microstructure on a silicon wafer via sub-pixel micro-scan micro-nano 3D printing technology to excite strong localized surface plasmon (LSP) effects - these effects confine terahertz fields at the subwavelength scale and synergistically enhance light-matter interaction with the topological metasurface effect; and (iii) introducing external laser fields to modulate carrier dynamics via the photoelectric effect and Floquet topological states, thereby further boosting detector performance. Experimental results demonstrate that the detector exhibits exceptional room-temperature performance: responsivity (Ra) reaches 41.96 A/W, noise-equivalent power (NEP) is as low as 11.86 pW/Hz1/2, detectivity (D*) maximizes at 26.67 x 109 cmHz1/2/W, the ultrafast carrier transit time is 0.4 picoseconds, and the broad spectral response width is 0.65 THz (covering the 6G communication band). Additionally, the silicon-based fabrication process is fully compatible with CMOS technology, facilitating high integration and large-scale production. This work provides a novel solution for the practical application of terahertz technology in 6G communication, real-time imaging, and high-sensitivity sensing.
Hopfions are a class of three-dimensional (3D) solitons which are built as vortex tori carrying intrinsic twist of the toroidal core. They are characterized by two independent topological charges, viz., vorticity S and winding number M of the intrinsic twist, whose product determines the Hopf number, , which is the basic characteristic of the hopfions. We QH = MS construct hopfion-like states (HLSs) as solutions of the 3D Gross-Pitaevskii equations (GPEs) for Bose-Einstein condensates in binary atomic gases. The GPE system includes the cubic mean-field self-attraction, competing with the quartic self-repulsive Lee-Huang-Yang (LHY) term, which represents effects of quantum fluctuations around the mean-field state, and a trapping toroidal potential (TP). Although our system exhibits two independent topological charges, it does not fully conform to the Hopf map structure, and therefore does not constitute hopfions in the complete sense. A systematic numerical analysis demonstrates that families of the states with S = 1, M = 0, i.e., QH = 0, are stable, provided that the inner TP radius R0 exceeds a critical value. Furthermore, HLSs with S = 1, M = 1-7, which correspond, accordingly, to QH = 1-7, also form partly stable families, including the case of the LHY superfluid, in which the nonlinearity is represented solely by the LHY term. On the other hand, the HLSs family is completely unstable in the absence of the LHY term, when only the mean-field nonlinearity is present. We illustrate the knot-like structure of the HLSs by means of an elementary geometric picture. For QH = 0, circles which represent the preimage of the full state do not intersect. On the contrary, for QH >= 1 they intersect at points whose number is identical to . The intersecting curves form multi-petal struc-QH tures with the number of petals also equal to QH.
Magnetic resonance wireless power transfer (WPT) with parity-time-(PT-) symmetry has been extensively studied due to its high transfer efficiency. However, conventional second-order PT-symmetric systems face several challenges in practical WPT applications. Due to near-field coupling, frequency splitting occurs in the strong coupling region, necessitating frequency tracking to maintain optimal transfer efficiency. Although the system can operate at a fixed frequency in the weak coupling region, the efficiency is significantly reduced. Strict PT-symmetry constraints also limit the system's flexibility in engineering applications. Additionally, severe field leakage from the transmitter coil in the strong coupling region leads to poor electromagnetic compatibility. Here, we demonstrate efficient WPT by implementing a bound state in the continuum (BIC) in a high-order non-Hermitian system based on a composite transmitter. BICs offer greater flexibility in practical applications as they do not require strict PT-symmetry. Remarkably, the optimized WPT system constructed with a composite transmitter maintains a stable pure real working frequency, reduces field leakage from the transmitter coil, and exhibits significant advantages over conventional second-order PT-symmetric systems. Our finding expands the application of BICs in high-efficiency WPT systems and provides a robust platform for realizing miniaturized and integrated high-order non-Hermitian WPT systems. BIC
Nonreciprocity plays a pivotal role in the design of optical and quantum devices. A key mechanism for achieving it lies in the breaking of Lorentz reciprocity. In this paper, we systematically investigate the scattering properties of a non-Hermitian system composed of an arbitrary-dimensional scattering center coupled to two semi-infinite leads. We first propose a general theorem that elucidates how symmetry constrains the transmission and reflection amplitudes. We show that parity-time (PT) symmetric systems can still exhibit reciprocal transmission despite the presence of non-Hermitian terms. The introduction of a magnetic flux that preserves parity symmetry and flux inversion symmetry can break Lorentz reciprocity and thus enable nonreciprocal transport. Based on detailed symmetry analysis, we construct a series of minimal models that demonstrate unidirectional transmission. Our results provide new insights into the mechanisms of nonreciprocal scattering and offer a theoretical foundation for the development of optical diodes and quantum isolators in non-Hermitian systems.
Extending attractive phenomena in non-Hermitian systems is crucial for advancing wave manipulation properties. In this study, we extend the phenomena of coherent perfect absorption-lasing (CPAL) as well as super-collimation, which were generally achieved at specific angles and frequencies, to broad-angle and broadband, respectively. In an airborne twodimensional phononic crystal, the combination of band folding and gain-loss modulation induces a parity-time phase transition, resulting in parity-time broken phase as well as a slab of exceptional points along one of the Brillouin zone boundaries. Based on the analysis of Hamiltonian, we design a Hilbert fractal space-coiling structure that minimizes the dispersion along this boundary. This approach significantly broadens the range of incident angles for CPAL and extends the frequency range for super-collimation. Our findings provide a design strategy for exploring wave manipulation phenomena in two-dimensional parameter spaces.
A theoretical model is presented to describe the surface acoustic wave-driven ferromagnetic resonance (SAW-FMR), systematically and effectively explaining the results of the previous experiment. In our model, the precessional cone angle delta 0 and the power attenuation triangle P are employed to represent the intensity of FMR. The expression of delta 0 can be divided into three independent parts: a constant term, a frequency-dependent term, and a surface acoustic wave (SAW) equivalent field term; each part is expressed explicitly with various parameters. To deeply understand the special field-sweeping SAW power attenuation spectrum patterns observed in previous experiments, we creatively interpret delta 0 as a combination of the resonant frequency spectrum and SAW equivalent field f0 |sin(2 phi M)|spectrum. It is the distinctive SAW equivalent term |sin(2 phi M)| that makes SAW attenuation spectrum an incomplete pattern compared to traditional electromagnetic wave (EMW). Furthermore, we discuss the influence of multiple factors on the SAW-FMR, including the external magnetic field magnitude and direction, SAW frequency and amplitude, as well as the magnetocrystalline anisotropy direction and distribution. To validate our theoretical model, micromagnetic simulations are also carried out in the corresponding situations.
The emergence of transformer-based artificial intelligence (AI) models has made a great impact on modern AI computing paradigms, where the attention mechanisms in transformer models dynamically generate weights and require computations involving global parameters. These requirements pose unprecedented challenges for memristor performance in in-memory computing, which demands memristor arrays with exceptional endurance, latency, energy consumption, and device uniformity. This perspective focuses on the alignment between AI computational requirements and memristor specifications, highlighting recent breakthroughs in materials, mechanisms, and applications for next-generation in-memory computing. Through this comprehensive analysis, our perspective provides critical insights into advancing memristor-based computing research toward practical AI applications. It also underscores key research priorities and the necessity for interdisciplinary collaboration to propel the future of AI innovation.
Guiding center theories are crucial in astrophysics, space plasmas, fusion research, and arc plasmas for addressing the multi-scale dynamics of magnetized plasmas. In this paper, we derive a new Lagrangian function of guiding center in 6D variables (X, X-center dot) different from the Littlejohn's one by employing two different approaches. Based on the new Lagrangian function, we prove that the guiding center dynamics can be generally described as a constrained canonical Hamiltonian system with two constraints in six dimensional phase space. By explicitly expressing the Lagrangian multipliers, we can reformulate the constrained Hamiltonian system into equivalent Hamiltonian-Dirac equations in coordinates (X, p) resides on a symplectic sub-manifold, ensuring the exact conservation of the symplectic structure. Thus, we identify the canonical coordinates of the guiding center. In this context, the guiding center behaves as a pseudo-particle with an intrinsic magnetic moment, effectively replacing charged particle dynamics over time scales longer than the gyro-period. The complete dynamical behaviors, including acceleration and force, of the guiding center pseudo-particle can be derived clearly and consistently from this theory. Additionally, this framework enables the systematic development of related theories, such as symplectic guiding center algorithms, canonical gyro-kinetic theory, and canonical particle-in-cell methods, enhancing the global accuracy of gyrokinetics and associated numerical techniques. The theory also sheds light on the origin of the intrinsic magnetic moment within the scope of classical mechanics. . In these coordinates, the guiding center dynamics' solution flow
Through analytic derivation within the nonequilibrium Green's function (NEGF) formalism, we present a comprehensive study of a quantum-coherent single-electron emitter. This emitter is based on a quantum circuit driven by periodic square-wave potentials with temporal period and angular frequency w = 27r/T. Our theoretical results reveal three key characteristics of the single-electron emitter: (i) the characteristic time alpha of the exponentially decaying current J(t)(a e-t/alpha) matches the intrinsic coherence time tau of the quantum dot; (ii) the Fourier spectrum of the current J(mw) carries information of both external driving amplitude U and internal energy levels of the quantum dot; (iii) the quantization of epsilon d fundamental Fourier component |J1|= 2ef ( f = 1/T) accompanies the half-quantized relaxation resistance Rq = h/(2e2), featuring quantized dynamics in AC transport through the single-electron emitter. These findings offers new perspectives into the dynamic properties of quantum-coherent AC transport. RC T
Precise control of lattice strain and buckling geometry at the nanoscale enables deterministic manipulation of the electronic properties of quantum materials. Low dimensional Bi(110) possesses topological properties and ferroelectricity, which are strongly tied to its atomic structure. Here, by fabricating an epitaxial heterostructure composed of 2-3 bilayer Bi(110) in black phosphorus (BP) structure and Fe3GeTe2 with hexagonal lattice structure, heterostrain and periodical variation of buckling height h are introduced into Bi(110) via interlayer interactions. Modulation of the electronic states and bandgap of ultra-thin Bi(110) are revealed the study of scanning tunneling microscopy and spectroscopy. The regulation of the electronic properties of Bi(110) by lattice stress and magnetic proximity effect of Fe3GeTe2 substrate are further explained by density functional theory calculations. The atomic scale straintronics method offers a strategy to modify the electronic properties of ultra-thin epitaxial films with potential applications in spintronics and nanoelectronics.
Rare-earth orthoferrites (RFeO3), which are canted antiferromagnets exhibiting weak ferromagnetism, are potential materials for spintronic devices. The temperature of spin reorientation transition (SRT) in Tm1-xPrxFeO3 with the increase of x, attributing to the exchange energy of being less than that of Tm3+-Fe3+. Both type-I of spin switching (SSW-I) and the type-II of spin switching (SSW-II) are observed along the a-axis when x = 0.15 and 0.2. The changes of magnetic interaction are analyzed through structural distortion and transforming Curi-Weiss fitting. A rare SSW-II phenomenon is observed along the c-axis during both the cooling and warming processes when x = 0.15, 0.25, 0.5. In addition, a weak ferromagnetic moment (WFM) component is observed despite the antiferromagnetic behavior at high temperature in Tm0.5Pr0.5FeO3 single crystal. The WFM decreases gradually with the increase in temperature, indicating the occurrence of SRT. And the field-induced spin switching (SSW) is observed along the a-axis at 70 K when x = 0.5. The magnetic properties of Pr3+ doped TmFeO3 single crystals are obviously different from TmFeO3 and PrFeO3 single crystals, indicating the complex magnetic interaction among , Pr3+ Tm3+ and Fe3+. The complex and abundant magnetic phenomena in Tm1-xPrxFeO3 single crystals offer significant potential for studying altermagnet and magneto-optical coupling, and are expected to become a new generation of spintronic devices. (x = 0, 0.15, 0.25, 0.5) single crystals shifts to a lower region Pr3+-Fe3+
Recently, hardware based bionic perceptual systems have attracted great attention. However, most reported bionic perceptual systems only have a single perceptual function, making it difficult to mimic multi-sensory perception process in real environments. Here, a bionic tactile-visualmorphic system (BTVMS) is proposed by integrating an indium gallium zinc oxide (IGZO) photoelectronic neuromorphic transistor (PNT) and a PDMS-ZnO based triboelectric nanogenerator (TENG). The IGZO-PNT exhibits stable electrical performance and can sensitively perceive optical stimuli. The PDMS-ZnO based TENG can convert mechanical stimuli into electrical signals, exhibiting a high sensitivity of similar to 0.75 V/kPa and good durability. The proposed BTVMS exhibits information encryption and decryption functions based on Morse code strategy. In addition, it can simulate the tactile and visual dual cognition behavior of brain. Thus, posttraumatic stress disorder behavior has been mimicked successfully. The present BTVMS provides a valuable idea for intelligent prosthetics and humanoid robots to achieve efficient bionic visual and tactile perceptions.
Nonlinear effects in the terahertz regime play a pivotal role in advancing terahertz wave generators with higher frequencies, particularly through harmonic generation processes. However, the development of efficient nonlinear terahertz materials that exhibit high conversion efficiency, compatibility with large-scale on-chip integration, and stable operation at room temperature remains a significant challenge. Graphene-assisted nonlinear metamaterials provide a promising platform for investigating nonlinear effects within the terahertz frequency regime. In this study, we present a transmission-mode nonlinear metamaterial-integrated device that synergistically combines the resonant characteristics of metamaterials with the nonlinear enhancement properties of graphene. This integrated structure enables efficient dual-frequency third harmonic generation (THG) at 9.535 THz and 10.959 THz, achieving a conversion efficiency of 0.127% under a pump intensity of MW/cm2. A comprehensive theoretical analysis is conducted to investigate both the linear and nonlinear operational characteristics of the integrated device. The enhancement mechanism of THG is systematically investigated by examining the electric field distributions and plasmonic resonance characteristics. Additionally, the influences of device structural parameters and terahertz wave incidence angle on the operational characteristics are thoroughly evaluated. The proposed graphene-based nonlinear metamaterial shows exceptional potential for broad applications in terahertz integrated systems and related photonic technologies.
Recent studies on the interplay between band topology and topological defects in real space offer an unprecedented opportunity to design photonic cavities. Here, we propose a concept of gradient dislocation by placing two chunks of square-lattice photonic crystals with the same width but differing by one period together, which is described by a one-dimensional Dirac equation with a position-dependent and sign-switching mass distribution. A photonic bound state, dubbed the Dirac cavity mode, localized at the center of the gradient dislocation is demonstrated. Compared to est modal area and a relatively high Q-factor, with its frequency demonstrating robustness against certain perturbations. We also discuss a potential application in index sensing by designing a coupled cavity-waveguide system based on the photonic Dirac cavity. Our work presents an ultracompact photonic cavity design and paves the way toward future photonic integrated circuits.
Moir & eacute; superlattices, classified as a supercell periodic structure configured from a periodic lattice overlaps with its twisted counterpart, have been demonstrated to exhibit many emergent linear and nonlinear phenomena like moir & eacute; induced flat bands, unconventional superconductivity, unique linear classical wave localization and nonlinear localized modes. Recent studies are, however, mainly focused on twisted bilayer structures, the static and nonequilibrium physics of trilayer moir & eacute; superlattices have remained largely unknown. We here consider trilayer moir & eacute; optical lattices by which Bose-Einstein condensates are trapped, and demonstrate theoretically the emergent flat bands and nonlinear phenomena - localized gap modes in form of gap solitons and vortices with a topological charge s = 1. We give a unified picture for constructing optimal (largest) photonic forbidden gaps in such trilayer moir & eacute; superlattices and reveal nonlinear localization mechanism therein. Computational studies demonstrated the robustness of these localized modes, enabling insightful inspections of moir & eacute; physics and exploring ongoing moir & eacute; photonics applications in twisted trilayer superlattices in optics and ultracold atoms.
Non-Hermitian systems have been extensively studied for their unique topological properties and dynamic behaviors. In this paper, we investigate the phenomenon of edge bursts in population dynamics with rock-paper-scissors interactions, focusing on the interplay between nonHermitian effects and biomass dissipation dynamics. We demonstrate that edge bursts occur when the energy bands form two distinct closed loops that do not intersect the real axis. Our findings reveal that the presence of non-dissipated sites is crucial for the formation of edge bursts, as they act as reservoirs, sustaining solitons near the boundaries and facilitating biomass transport to the edges. This study provides new insights into the behavior of non-Hermitian systems with open boundaries and asymmetric interactions, contributing to a broader understanding of complex phenomena in such systems.
