We demonstrate a 2 μm ultrafast fiber chirped-pulse amplifier (FCPA) utilizing dual-wavelength hybrid pumping at 793 nm and 1570 nm. Seeded by a high-power nonlinear polarization rotation oscillator, hybrid pumping improved optical conversion efficiency by 9.4% compared with single-wavelength pumping. Stimulated Raman scattering was observed with a 20-W 793-nm pump but suppressed under 30 W hybrid pumping. A spatial spectral modulator in the pulse stretcher optimized pulse quality. The system delivered 235 fs pulses at 5.2 W up to 11.23-W, 51.6-MHz, 445-fs, 1978-nm, demonstrating an efficient route to high-power 2-μm femtosecond fiber lasers.

Magnetic circular dichroism utilizing electrons or X-rays serves as a powerful tool for the investigation of magnetism in ferromagnets, but antiferromagnets pose a severe challenge to the technique due to their vanishing net magnetization. Although transmission electron microscopy has demonstrated the atomic-scale characterization of antiferromagnetism using elastically scattered electrons, separating the weak magnetic signal from the dominant electrostatic background remains challenging, and applicability is largely limited to perfect crystals. Here we develop atomic-column-resolved electron magnetic circular dichroism to resolve antiferromagnetic order using a scanning transmission electron microscope. By exploiting chirality around individual magnetic atomic columns, we localize the magnetic circular dichroism signals around the transmitted electron beam with enhanced strength and signal-to-noise ratio, enabling atomic-column magnetic measurements. Applying this technique to antiferromagnets, we not only distinguish the characteristic G-type and C-type antiferromagnetic orderings in DyFeO3 and α-Fe2O3 but also identify a one-unit-cell-thick magnetic dead layer at the buried DyScO3-SmFeO3 interface. Our work establishes a readily accessible method for atomic-scale magnetic order mapping, with potential applications in fields such as interfacial magnetism, topological magnetism, antiferromagnetism and altermagnetism.

Magnetic skyrmions, topologically protected spin textures, are promising for both fundamental studies of topological magnetism and spintronic applications in data storage, logic processing, true random number generators, and neuromorphic computing. Yet, their energy dissipation, a key metric for evaluating manipulation efficiency and dynamics, remains elusive. Here, magnetotropic dissipation in B20 MnSi is characterized by dynamic cantilever magnetometry (DCM). Magnetotropic dissipation in the skyrmion phase is about one order of magnitude smaller than in topologically trivial helical and conical states, which is attributed to the topological characteristic that preserves spin configurations and minimizes energy loss to the electron/ phonon heat bath, as confirmed by micromagnetic simulations. A magnetotropic dissipation phase diagram is further constructed, revealing little temperature dependence of skyrmion magnetotropic dissipation, indicative of negligible magnonic contributions to the magnetotropic dissipation process. Our results reveal the low magnetotropic dissipation characteristic and underlying mechanisms of skyrmions, and demonstrate that DCM can resolve dissipation down to 7×10−14 kg/s, enabling detailed investigations of magnetic materials at microscale dimensions.

Scalable quantum photonic technologies require single-photon emitters whose positions and emission energies can be engineered simultaneously. Hexagonal boron nitride (hBN) is an attractive room-temperature host, but deterministic creation of spectrally reproducible emitters remains challenging. Here, we use a standard scanning electron microscope as a direct-writing tool to activate bright green single-photon emitters in hBN at predefined sites, without ion implantation or post-fabrication thermal annealing. The written emitters exhibit reproducible zero-phonon-line emission centered near 536 nm, room-temperature antibunching with g(2)(0) as low as 0.08, high brightness, strong linear polarization, and stable emission. Thickness-dependent activation, stacking experiments, cathodoluminescence spectroscopy, and first-principles calculations support a carbon-related defect complex as the most plausible origin of the emission. As a proof of nanophotonic compatibility, we further activate emitters in a nanoparticle-on-mirror plasmonic nanocavity and observe photoluminescence enhancement accompanied by shortened emission lifetimes. These results establish electron-beam direct writing as a practical route to site-selective, spectrally uniform green quantum emitters in hBN, offering a promising basis for integrated room-temperature quantum photonic architectures.

Objective Among all the mechanisms in realizing the passively mode-locked fiber lasers, the nonlinear amplifying loop mirror (NALM) mechanism can achieve better systematic robustness and long-term operating stability of the generated mode-locked fiber laser. However, utilizing the NALM to realize the mode-locked laser, the self-starting state of the realized mode-locked laser needs to be triggered, accompanied with severe optical pulse splitting. Multiple investigations have been implemented in managing the intra-cavity dispersion and the nonlinear phase accumulating process to optimize the self-starting state and single-pulse mode-locked operating performance. The intra-cavity loss and nonlinear phase accumulation process are highly related with the modulation depth of the NALM. However, the influences of the modulation depth of the NALM in optimizing the operating performance of the mode-locked Yb-doped fiber laser are rarely reported to our known. Based on employing different optical coupling ratios of the fiber coupler to manage the modulation depth of the NALM, the optical dynamics of the mode-locked pulses can be clearly analyzed. The optimized coupling ratio can be further proposed to realize a truly optimized all-PM fiber NALM laser, satisfying the application requirements. Methods In this paper, detailed investigations are carried out on a mode-locked NALM fiber laser with varying modulation depths to achieve further optimized mode-locked performance. An in-house-built fiber oscillator operating at repetition frequency of 40.02 MHz is first realized using a 60 & ratio;40 2 & times;2 optical coupler under a pump power of 67 mW, after the net cavity dispersion is optimized to -0.03598 ps(2). Under the same net cavity dispersion and loss characteristics, the NALM laser is subsequently constructed by changing the coupling ratio of the 2 & times;2 fiber coupler to 70 & ratio;30, 80 & ratio;20, and 90 & ratio;10. Detailed investigation and analysis are conducted to determine the optimal coupling ratio range for realizing an improved NALM laser. The 70 & ratio;30 2 & times;2 optical coupler is ultimately adopted, yielding a net cavity dispersion of -0.0269 ps(2), which ensures reliable operating performance suitable for the aforementioned applications. Results and Discussions When the coupling ratios are set to 90 & ratio;10, 80 & ratio;20, 70 & ratio;30, and 60 & ratio;40, the corresponding changes in single-pulse mode-locked pump power are 6, 9, 12, and 12 mW, respectively. Given that the net cavity dispersion of the NALM laser is optimized for a coupling ratio of 60 & ratio;40, it is evident that the optimal coupling ratio range for this fiber NALM laser lies around 70 & ratio;30. This observation is further supported by the measured optical spectra and autocorrelation traces. The self-starting NALM laser is further optimized using the 70 & ratio;30 fiber coupler, and the net cavity dispersion is adjusted to -0.0269 ps(2) based on the pump power thresholds for establishing and losing the single-pulse mode-locked state. Single-pulse mode-locked operation is achieved when the pump power is reduced to 52 mW, while the mode-locked state transitions to continuous-wave operation when the pump power falls below 36 mW. Consequently, a stable single-pulse mode-locked state is maintained over a pump power range of 16 mW. With the 70 & ratio;30 coupling ratio, the mode-locked spectra exhibit 3-dB spectral full widths at half-maximum (FWHM) of 2.54 nm and 9. 79 nm at the polarization beam splitter (PBS) port and the transmission port, respectively. The optimized pump power threshold for achieving single-pulse mode-locked operation with the 70 & ratio;30 fiber coupler is 52 mW, corresponding to output signal powers of 3.36 mW from the PBS port and 3.23 mW from the transmission port. The corresponding pulse widths, calculated assuming a Gaussian pulse shape, are 2654.7 fs and 1245.2 fs, respectively, and the measured radio frequency (RF) signal-to-noise ratio is 76.59 dB. A broadband RF spectrum measured over a span of 3 GHz reveals no obvious RF spectral modulation, indicating reliable operating performance of the 70 & ratio;30 NALM laser. The calculated root mean square (RMS) stability is 0.24%@2 h, confirming that the 70 & ratio;30 coupling ratio is well suited for realizing a mode-locked NALM laser. Conclusions In conclusion, an ytterbium-doped, stretched-pulse mode-locked fiber oscillator is realized by employing a NALM with varying modulation depths. A comprehensive analysis is conducted to investigate the influence of the optical modulation depth on the output characteristics of this in-house-built NALM laser. The modulation depth is adjusted using different optical couplers with coupling ratios of 60 & ratio;40, 70 & ratio;30, 80 & ratio;20, and 90 & ratio;10. A mode-locked fiber laser with a repetition frequency of 40.02 MHz and a central wavelength of 1030 nm is first achieved using a 60 & ratio;40 fiber coupler under a net cavity dispersion of -0.03598 ps(2), delivering single-pulse mode-locked operation with pump power ranging from 55 mW to 67 mW. Further detailed investigations are also conducted on the mode-locked NALM laser with coupling ratios of 70 & ratio;30, 80 & ratio;20, and 90 & ratio;10. Based on the experimental results, the coupling ratio around 70 & ratio;30 is identified as the optimal choice for realizing the NALM laser. The corresponding net cavity dispersion is optimized to -0.0269 ps(2) according to the pump power thresholds for achieving and losing the single-pulse mode-locked state. Single-pulse mode-locked operation is attainable with pump power varying from 36 mW to 52 mW. Two ultrashort mode-locked pulse trains are delivered from the two output ports, exhibiting a calculated RMS stability of 0.24%@2 h, which ensures reliable operating performance suitable for applications like the optical metrology, biological imaging, microstructure processing, and strong-field physics.

Fiber optical parametric oscillators (FOPOs) offer coherent laser outputs with broad wavelength tunability, high conversion efficiency, and stable operation, which are widely applied in biomedical imaging and wavelength conversion. Here, we report on a high-power, narrow-bandwidth, 800-950 nm FOPO pumped by a picosecond spectrally managed Yb-doped fiber laser. The home-built polarization-maintaining (PM) fiber seed laser was mode-locking based on the nonlinear amplifying loop mirror (NALM). The narrow-bandwidth, high-power fiber pump laser for the FOPO was realized by utilizing the extra-cavity amplified spectral filter consisting of the 4-f spectral filter and the double-pass fiber amplifier. Numerical simulations of the employed four-wave mixing (FWM) process were performed and validated experimentally. The FOPO dynamics governed by the FWM parametric gain were analyzed. The realized FOPO source can deliver a signal laser with central wavelength tuning from 800 to 950 nm, with <1-nm optical spectral bandwidth and >100-mW optical average power. The Yb-doped fiber pump laser can deliver 1040-1060 nm tunable picosecond pulses with watt-level average power and ∼1-nm spectral bandwidth. This compact, robust FOPO laser source fulfills the key requirements for biomedical imaging and nonlinear frequency conversion.

Topological phononics extends the foundational concepts of topological condensed matter physics to the realm of lattice vibrations and classical mechanical waves, unlocking robust, defect-immune states and phenomena beyond the reach of conventional phononic engineering. This review provides a unified, systematic framework for understanding topological phonons across natural and artificial systems, spanning solid-state materials, acoustic/mechanical metamaterials, and non-Hermitian platforms. We cover the core theoretical principles – from Berry curvature and symmetry-protected topological invariants to bulk-boundary correspondence – alongside experimental advances in probing topological phonon states via inelastic scattering and momentum-resolved techniques for solid-state phonons as well as pump-probe measurements in acoustic/mechanical metamaterials. Key topics include Weyl/Dirac/nodal-line phonons in crystalline solids, symmetry-engineered topological phases in metamaterials, non-Hermitian effects (exceptional points, skin effect), and emergent directions such as Floquet engineering, synthetic dimensions, and real-space topological textures (skyrmions, merons). We also highlight technological applications in robust waveguides, on-chip surface-acoustic-wave devices, and acoustofluidics, while outlining future challenges and opportunities in quantum phononics, nonlinear topological phenomena, and interdisciplinary integration with photonics and electronics. This review serves as a comprehensive guide across physics, materials science, and engineering, bridging fundamental theory with cutting-edge experiments and innovations in topological phononics.

(2D) van der Waals (vdW) superconductors provide a platform for investigating unconventional superconductivity, topological states, and low-power quantum devices. However, due to their extremely small volume and weak magnetic signals, their superconductivity has primarily been assessed through zero resistance, while the Meissner effect remains largely unexplored. Here, we demonstrate that dynamic cantilever magnetometry (DCM) can be used to probe the intrinsic Meissner diamagnetism in 2D vdW superconductors. A theoretical model is first established to quantitatively extract magnetization and susceptibility. Building on this, using 2M-WS2 as a model system, a clear magnetization hysteresis loop characteristic of type-II superconductivity is resolved. Meanwhile, susceptibility is also detected down to a thickness of 5.7 nm, revealing a screening efficiency of about 89.9% at 4.6 mT, indicative of nearly complete diamagnetic screening. We analyze that DCM achieves a magnetization sensitivity of ∼ 1.1 × 10 - 17 A · m 2 $\sim\!\! 1.1 \times {{10}^{ - 17}}\ {\mathrm{A}} \cdot {{{\mathrm{m}}}^2}$ and susceptibility sensitivity of ∼ 9.4 × 10 - 17 A · m 2 / T $\sim\! 9.4 \times {{10}^{ - 17}}\ {\mathrm{A}} \cdot {{{\mathrm{m}}}^2}/{\mathrm{T}}$ . Our results provide crucial magnetic signatures of the Meissner effect in 2D vdW superconductors and highlight the capability of DCM for magnetic validation of superconductivity in low-dimensional materials.

We demonstrate an 80 MHz, 350 mW, 120 fs, 770 nm femtosecond laser based on a nonlinear compressed 1540 nm femtosecond fiber laser. The home-built 1540 nm fiber laser, delivering 80 MHz, 2.69 W, 269 fs laser pulses, was realized by employing spectral pre-modulation and pre-chirp management inside an Er/Yb co-doped fiber power amplifier. The subsequent nonlinear fiber pulse compression stage was utilized to further nonlinearly compress the pulse duration to 128 fs based on the Gaussian assumption. Detailed numerical simulation was also implemented to investigate the optical dynamics of the nonlinear compression process. Finally, a 0.5 mm thick fan-out periodically poled lithium niobate (PPLN) crystal was utilized to generate the frequency-doubled, 350 mW, 770 nm laser pulses with a 120 fs pulse duration based on the Gaussian assumption.

The competition between incompatible oxygen octahedral tilting modes across heterointerfaces offers a powerful, yet underexplored, avenue to discover emergent phenomena. Here, we report an atomically switchable giant spontaneous Hall effect (SHE) in nTbScO3/10SrIrO3 superlattices. By controlling the TbScO3 spacer thickness with a single-unit-cell precision, we observed an abrupt increase of SHE at n = 1, above which SHE is significantly suppressed to a Berry curvature dominated level. Synchrotron x-ray diffraction and scanning transmission electron microscopy reveal that this switching behavior arises from a nontrivial modulation of octahedral tilting in the superlattice unit, leading to an incipient modulation in magnetic structure.

Quantized charge pumping in one-dimensional chiral wires has been widely studied in the context of topological physics in (1 + 1)-dimensional synthetic space, yet the role of orbital and spin degrees of freedom remains largely unexplored. Here, we show that topological charge pumping in insulating chiral systems intrinsically generates orbital and spin polarization, providing a new perspective on spin-selective transport in chiral materials, often associated with chirality-induced spin selectivity. Using time-dependent Schrödinger dynamics of multiorbital tight-binding models driven by circularly polarized light, we identify two key results. First, the screw-like geometry enables a single-parameter topological charge pumping. Second, while the energy gap remains open throughout the pumping cycle, Berry phase driven dynamics induces nonequilibrium orbital polarization. Through spin-orbit coupling, this orbital response is partially converted into spin polarization. By analogy between synthetic (1 + 1)- and two-dimensional topological insulators, we suggest that nontrivial spin-orbital dynamics may accompany anomalous quantum charge Hall states.

Magnetic skyrmions and related topological spin textures have emerged as a central topic in condensed-matter physics, combining fundamental significance with potential for transformative applications in spintronics, magnonics, and beyond. Over the past decade, advances in material platforms, imaging techniques, theoretical modeling, and device concepts have established skyrmionics as a rapidly expanding field. At the same time, challenges remain in stabilizing, controlling, and integrating such textures into functional architectures, while novel phenomena such as antiskyrmions, higher-order skyrmions, hopfions, and antiferromagnetic textures arise. The 2026 Skyrmionics Roadmap represents a collective effort of many authors, providing a comprehensive perspective on the current state-of-the-art and the outlook for the coming years. In 33 focused sections, each co-authored by two researchers, we chart progress in theory and modeling, material systems, skyrmion dynamics, and skyrmion technologies. By offering a consolidated vision, this Roadmap aims to guide both fundamental research and application-driven efforts, accelerating the transition of skyrmionics from conceptual breakthroughs toward practical technologies.

The development of low-noise, high-sensitivity magnetic sensors is essential for applications such as automotive systems, biomedical imaging, and magnetic microscopy. However, sensor performance has long been impeded by a fundamental constraint that noise and sensitivity increase concomitantly, which imposes a performance limit. Here, we show that this limit can be overcome by engineering spin-texture dynamics. While maintaining high sensitivity, the sensor noise is demonstrated to decrease inversely with enhanced spin-texture dynamics. Leveraging this mechanism, using synthetic ferrimagnets with accelerated spin-texture dynamics, low-noise and high-sensitivity anomalous-Hall sensors are constructed. With an active sensing area of 20×20  μm^{2}, the device demonstrates a field detectability of 15.7  nT/√Hz at 1 Hz, nearly an order of magnitude improvement over existing sensors based on ferromagnetic materials. Our results establish active control of spin textures as a general pathway to ultrasensitive, low-noise magnetic sensing platforms.

A magnetic heliknoton is the three-dimensional counterpart to the two-dimensional magnetic skyrmion, and serves as a pivotal topological soliton for extending topological magnetism into three dimensions. However, its experimental realization remains elusive. Here we report the controlled nucleation of a magnetic heliknoton in the chiral magnet FeGe at zero magnetic field, achieved through nanoscale current-pulse excitation. By combining angle-dependent quantitative electron holography with micromagnetic simulations, we resolve the three-dimensional spin texture of the heliknoton. In particular, the heliknoton exhibits current-driven collinear motion without the Hall effect. Our findings establish a readily accessible experimental platform for further exploration of three-dimensional topological solitons and highlight their potential for practical applications. Magnetic heliknotons are hopfions embedded in helical spin backgrounds. Current-induced nucleation and Hall-effect-free motion of isolated magnetic heliknotons is demonstrated in the chiral magnet FeGe.

Strain defect is crucial to the physical properties of solid materials. Among them, strain glass induced by defect engineering provides an important paradigm for nanoscale domain manipulation. Here, we propose purely mechanical moiré strain Skyrmions, a topologically protected elastic textures whose motion can be controlled by interlayer sliding and the chirality of the moiré bilayer. Using an empirical continuum elastic model combined with symmetry analysis, we demonstrate the Skyrmion lattice structure as the elastic ground state. Under interlayer sliding, these moiré strain Skyrmions exhibit the Skyrmion Hall effect of transverse motion, with a Hall angle determined by bilayer chirality and inversely proportional to the moiré twist angle. Our work establishes interlayer sliding as an efficient, low-energy control knob for topological excitations, offering a new paradigm for designing chiral-material-based information transport devices.

The classical field description of phonon spin relies on the invariance of a continuous elastic field under infinitesimal rotation. However, a local medium element in the continuous field may contain large numbers of vibrational particles at microscopic level, like for complex lattices with many atoms in a unit cell. We find this causes the phonon spin in real materials no longer a simple sum of each atom rotation, but a collective interference of many atoms, since phonons are phase-coherent vibrational modes across unit cells. We demonstrate the collective interference phonon spin manifested as the dipole moment rotating (DMR) of charge-polarized unit cell, by deriving the infrared circular dichroism (ICD) with phonon-photon interaction in complex lattices. We compare the DMR with the local atom rotation without interference, and exemplify their distinct ICD spectrum in a chiral lattice model and two realistic chiral materials. Detectable ICD measurements are proposed in quartz with Weyl phonon near Gamma point. Our study underlies the important role of collective interference and uncovers a deeper insight of phonon spin in real materials with complex lattices.

Computational spectroscopy with modulated light spectrum is especially well-suited for application scenarios where active illumination is needed. Most of the existing computational spectroscopy, however, uses ambient illumination and modulates the signal spectrum that is reflected or transmitted from objects, mainly because of the lack of a light source with effective spectrum modulation. Here, we present a novel computational spectrometer featuring light-source spectrum modulation achieved through polarization-induced nonlinear spectrum modulation, offering a compact and low-cost system apparatus. The modulated spectrum can evolve periodically by managing polarization-induced nonlinear phase as well as pump power, within the range from 1000 nm to 1100 nm. Combining wavelength multiplexing and compressed sensing, we can achieve a minimum spectral resolution of 0.2 nm, which is comparable to the commercial spectrometer. The utilized objects with sparse and non-sparse spectra are successfully reconstructed both in simulation and experiment, within an effective reconstruction spectral range from 1021 nm to 1077 nm.

Magnetic skyrmions are topologically protected spin textures with emergent particle-like behaviors. Their dynamics under external stimuli is of great interest and importance for topological physics and spintronics applications alike. So far, skyrmions are only found to move linearly in response to a linear drive, following the conventional model treating them as isolated quasiparticles. Here, by performing time and spatially resolved resonant elastic X-ray scattering of the insulating chiral magnet Cu2OSeO3, we show that for finite-sized skyrmion crystallites, a purely linear temperature gradient not only propels the skyrmions but also induces continuous rotational motion through a chiral lattice torque. Consequently, a skyrmion crystallite undergoes a rolling motion under a small gradient, while both the rolling speed and the rotational sense can be controlled. Our findings offer a new degree of freedom for manipulating these quasiparticles toward device applications and underscore the fundamental phase difference between the condensed skyrmion lattice and isolated skyrmions.

Nonlinear optical (NLO) effects in materials with band crossings have attracted significant research interests due to the divergent band geometric quantities around these crossings. Most current research has focused on band crossings between the valence and conduction bands. However, such crossings are absent in insulators, which are more relevant for NLO applications. In this Letter, we demonstrate that NLO effects can be significantly enhanced by band crossings within the valence or conduction bands, which we designate as "deep band crossings" (DBCs). As an example, in two dimensions, we show that shift conductivity can be substantially enhanced or even divergent due to a mirror-protected "deep Dirac nodal point." In three dimensions, we propose GeTe as an ideal material where shift conductivity is enhanced by "deep Dirac nodal lines." The ubiquity of this enhancement is further confirmed by high-throughput calculations. Other types of DBCs and NLO effects are also discussed. By engineering band crossings between arbitrary bands, our Letter offers a simple, practical, and universal way to enhance NLO effects.

Photomagnetic effects (PMEs), intrinsic to transition metals, arise from the interaction between light-induced angular momentum and electronic spin. These effects are suppressed in noble metals with high symmetry and electron density. Introducing chiral structures can induce photomagnetic-chiral anisotropy (PMChA) of metals by linking chirality and spin dynamics. However, a theoretical explanation remains elusive. Here, we investigated the mechanism of PMChA in tetrahelix-stacked chiral nanostructured Au chains (CNACs) using first-principles calculations. Nonequilibrium Green's function calculations reveal that chiral potentials enhance spin channel asymmetry by amplifying spin-orbit coupling (SOC)-induced spin splitting. Real-time time-dependent density functional theory simulations further identify SOC as the bridge connecting chiral spintronics to PMEs, where chirality-driven spin flips from asymmetric geometries generate opposing photomagnetic fields in materials of different handedness. These findings are consistent with experimental observations in chiral nanostructured gold films and provide theoretical guidance for designing metallic spintronic devices.