arXiv subjects

Fengyuan Yang

Publications and source records attributed to Fengyuan Yang.

At least 19 recordsLinked to original sources

arXiv2026

Intelligent Reflecting Surfaces for THz Communications: Fundamentals, Key Solutions, and System Prototyping

Intelligent reflecting surfaces (IRSs) have emerged as a cost-effective technology for terahertz (THz) communications by enabling programmable control of the wireless environment. This paper provides a comprehensive overview of IRSs-aided THz communications, covering hardware designs, advanced signal processing techniques, and practical deployment strategies. It first examines key THz reconfigurable metasurface architectures, including electronic, optical, phase-change material, and micro-electromechanical systems (MEMS)-based implementations, highlighting their reconfiguration mechanisms and challenges. Then, fundamental effects including near field and beam squint in wideband THz systems are analyzed, along with their impacts on system performance. The paper further explores conventional and beam-squint-assisted channel estimation methods, innovative beam management strategies, and deployment considerations across large- and small-scale scenarios. Practical experiments at 220 gigahertz (GHz) validate the effectiveness of IRS in improving signal strength and communication reliability for both single-user and multi-user setups.

eess.SP↗

arXiv2026

Dislocation-templated antiferromagnetic domains in epitaxial NiO

Controlling antiferromagnetic domains is essential for spintronics, yet deterministic manipulation remains challenging due to their lack of net magnetization. Here, we utilize scanning electron microscopy electron channeling contrast imaging (ECCI) to demonstrate a robust structural memory effect in epitaxial NiO/MgO(001), where antiferromagnetic twin-domain walls (DWs) are deterministically pinned at the nanoscale by interface dislocation networks. Thermal cycling across the Neel temperature reveals that while DW contrast completely vanishes in the paramagnetic phase, the features re-emerge at identical spatial locations upon cooling. Diffraction-vector-dependent ECCI demonstrates that domain contrast stems from localized rhombohedral magnetostrictive strain fields. By tracking a film thickness series from 23 to 60 nm, we resolve an explicit transition in oxide relaxation mechanics. A primary slip system initiates strain relaxation via interface misfit dislocations (MDs) tracking along <100>. At greater thicknesses, rising critical strain prompts threading segments to cross-slip onto secondary or higher-index planes, depositing a wavy network of zig-zag MD lines deviated toward <110>. Quantitative image analysis reveals that DW area fractions directly track the local density and spatial configuration of the evolving MD networks, providing a framework for defect-engineering antiferromagnetic textures using one-dimensional defects.

cond-mat.mtrl-sci↗

arXiv2026

Rational Communication Shapes Morphological Composition

Human languages expand vocabularies by combining existing morphemes rather than inventing arbitrary forms. Communicative efficiency shapes lexical systems at multiple levels (Gibson et al., 2019), yet morphological composition -- combining morphemes through compounding or affixation -- has rarely been modeled as a historically situated speaker choice among competing morpheme sequences, leaving unanswered why a language settles on one morpheme combination over other plausible alternatives. We ask whether a trade-off between listener recoverability and speaker production cost can predict attested compositions over contemporaneously available alternatives. Here we show, within the Rational Speech Act (RSA) framework (Frank & Goodman, 2012; Goodman & Frank, 2016) using a time-indexed lexicon constructed from Corpus of Historical American English (COHA) and Corpus of Contemporary American English (COCA), that across 4323 naturally occurring English compounds and derivations spanning 1820--2019, attested compositions are systematically ranked above unattested alternatives generated from contemporaneously available morphemes. Models integrating semantic informativeness with production cost outperform semantic-only and cost-only baselines on Mean Reciprocal Rank (MRR) and top-k accuracy (Acc@k), with the advantage of the Pragmatic Speaker model ($S_1$) over the semantic-only baseline growing as the candidate set expands, where meaning alone leaves morphological choice underdetermined. These findings suggest that lexicalization reflects a communicative trade-off between expressiveness and efficiency, extending rational accounts of communication from utterance-level choice to the internal structure of words.

cs.CL↗

arXiv2026

Sub-Nanosecond Electrical Pulse Switching of an Easy Plane Antiferromagnetic Insulator

Electrical switching of antiferromagnets (AFM) is critical for AFM spintronics. However, electrical pulse-induced Neel vector reorientation in AFM insulators, while predicted to occur at much faster timescales than ferromagnetic switching, has only been demonstrated in the quasi-DC regime. Here we report reliable current-induced AFM switching in Pt/$α$-Fe$_2$O$_3$ bilayers using electrical pulses with various durations spanning three orders of magnitude down to 0.3 ns. Together with COMSOL simulations of temperature distributions in our samples for various pulse widths, our results suggest that thermally-assisted spin-orbit torque likely play an important role for sub-ns pulses. This work demonstrates the viability of electrical switching of AFM spins using sub-ns pulses.

physics.app-ph↗

arXiv2026

ONE-SHOT: Compositional Human-Environment Video Synthesis via Spatial-Decoupled Motion Injection and Hybrid Context Integration

Recent advances in Video Foundation Models (VFMs) have revolutionized human-centric video synthesis, yet fine-grained and independent editing of subjects and scenes remains a critical challenge. Recent attempts to incorporate richer environment control through rigid 3D geometric compositions often encounter a stark trade-off between precise control and generative flexibility. Furthermore, the heavy 3D pre-processing still limits practical scalability. In this paper, we propose ONE-SHOT, a parameter-efficient framework for compositional human-environment video generation. Our key insight is to factorize the generative process into disentangled signals. Specifically, we introduce a canonical-space injection mechanism that decouples human dynamics from environmental cues via cross-attention. We also propose Dynamic-Grounded-RoPE, a novel positional embedding strategy that establishes spatial correspondences between disparate spatial domains without any heuristic 3D alignments. To support long-horizon synthesis, we introduce a Hybrid Context Integration mechanism to maintain subject and scene consistency across minute-level generations. Experiments demonstrate that our method significantly outperforms state-of-the-art methods, offering superior structural control and creative diversity for video synthesis. Our project has been available on: https://martayang.github.io/ONE-SHOT/.

cs.CV↗

arXiv2026

NarrativeLoom: Enhancing Creative Storytelling through Multi-Persona Collaborative Improvisation

Large Language Models show promise for AI-assisted storytelling, yet current tools often generate predictable, unoriginal narratives. To address this limitation, we present NarrativeLoom, a multi-persona co-creative system grounded in Campbell's Blind Variation and Selective Retention theory. NarrativeLoom deploys specialized AI personas to generate diverse narrative options (blind variation), while users act as creative directors to select and refine them (selective retention). We designed a controlled study with 50 participants and found that stories co-authored with NarrativeLoom were not only perceived by users as more novel and diverse but were also objectively rated by experts as significantly better across all Torrance Test creativity dimensions: fluency, flexibility, originality, and elaboration. Stories are significantly longer with richer settings and more dialogue. Writing expertise emerged as a moderator: novices benefited more from structured scaffolding. This demonstrates the value of theory-informed co-creative systems and the importance of adapting them to varying user expertise.

cs.HC↗

arXiv2025

Broad-Range Tuning of Ferroelectric Switching of LaxBi1-xFeO3 Epitaxial Films via Digital Doping using Off-Axis Co-Sputtering

To investigate the scope of ferroelectric behavior in La-substituted BiFeO3 films, LaxBi1-xFeO3 epitaxial films were synthesized using off-axis co-sputtering on SrTiO3(001) and DyScO3(110) substrates with a SrRuO3 bottom electrode layer. A digital-doping deposition method was used to enable precise control and continuous tuning of La concentration in high-quality LaxBi1-xFeO3 films across a wide range of x = 0.05-0.60, which was systematically investigated using piezoresponse force microscopy. Robust and reversible out-of-plane ferroelectric switching has been observed up to x = 0.35, while films with x $\geq$ 0.37 exhibit no measurable ferroelectric behavior, indicating a sharp ferroelectric-to-paraelectric phase transition between x = 0.35 and 0.37. This represents the highest reported La concentration in LaxBi1-xFeO3 films that retains ferroelectric ordering, highlighting opportunities to engineer ferroelectric and multiferroic properties in complex oxide heterostructures.

cond-mat.mtrl-sci↗

arXiv2025

Magneto-Optical Analysis of Magnetic Anisotropy in Ultrathin Tm$_{3}$Fe$_{5}$O$_{12}$/Pt Bilayers

Magnetic bilayers consisting of an epitaxially grown ferrimagnetic insulator and a heavy metal layer are attractive for spintronic application because of the opportunity for electric control and read-out of spin textures via spin orbit torque. Here, we investigate ultrathin thulium iron garnet (TmIG)/Pt bilayers when the TmIG layer thickness is 3 nm and below using a sensitive Sagnac magneto-optical Kerr effect technique. We compare the hysteresis loops from out-of-plane and in-plane applied magnetic fields. The preferred magnetization orientation evolves with the TmIG thickness and the presence of the Pt overlayer. We quantify the evolution of the magnetic anisotropy in these ultrathin films and find a significant change even when the TmIG thickness is varied by less than 1 nm. In these ultrathin films, the presence of a Pt overlayer changes the effective anisotropy field by more than a factor of 2, suggesting that the interfacial anisotropy at the Pt/TmIG interface plays a critical role in this regime.

cond-mat.mtrl-sci↗

arXiv2025

Coherent Spin Pumping Originated from Sub-Terahertz Néel Vector Dynamics in Easy Plane α-Fe2O3/Pt

We present a thorough study of spin-to-charge current interconversion in bulk and thin films of (0001) α-Fe2O3 /Pt heterostructures by means of all-optical polarization-controlled microwave excitation at sub-Terahertz frequencies. Our results demonstrate that coherent spin pumping is generated through excitations of both the acoustic and optical modes of antiferromagnetic resonance, provided that the corresponding selection rules are met for the relative orientation between the microwave magnetic field h_ac and the magnetic moment m_0 of the Hematite. In particular, our results unanimously show that while a microwave field with h_ac perpendicular to m_0 pumps a net spin angular momentum from the acoustic mode, spin pumping from the optical mode is only enabled when h_ac parallel to m_0, as expected from the selection rules imposed by the Neel vector dynamics. Our results support the current understanding of spin mixing conductance in antiferromagnetic/non-magnetic interfaces, contrary to recent reports where the absence of spin pumping from the optical mode in Hematite was interpreted as a cancellation effect between the diagonal and off-diagonal components of the spin mixing conductance. We also provide an explanation for the previously reported observations and show how the optical spin pumping actually vanishes for thin films, which we speculate being either due to an increased level of inhomogeneities or to insufficient film thickness for the optical mode to fully realize.

cond-mat.mes-hall↗

arXiv2024

Humans as Checkerboards: Calibrating Camera Motion Scale for World-Coordinate Human Mesh Recovery

Accurate camera motion estimation is essential for recovering global human motion in world coordinates from RGB video inputs. SLAM is widely used for estimating camera trajectory and point cloud, but monocular SLAM does so only up to an unknown scale factor. Previous works estimate the scale factor through optimization, but this is unreliable and time-consuming. This paper presents an optimization-free scale calibration framework, Human as Checkerboard (HAC). HAC innovatively leverages the human body predicted by human mesh recovery model as a calibration reference. Specifically, it uses the absolute depth of human-scene contact joints as references to calibrate the corresponding relative scene depth from SLAM. HAC benefits from geometric priors encoded in human mesh recovery models to estimate the SLAM scale and achieves precise global human motion estimation. Simple yet powerful, our method sets a new state-of-the-art performance for global human mesh estimation tasks, reducing motion errors by 50% over prior local-to-global methods while using 100$\times$ less inference time than optimization-based methods. Project page: https://martayang.github.io/HAC.

cs.CV↗

arXiv2024

Large spin-orbit torque in a-plane $α$-Fe$_{2}$O$_{3}$/Pt bilayers

Realization of efficient spin-orbit torque switching of the Néel vector in insulating antiferromagnets is a challenge, often complicated by spurious effects. Quantifying the spin-orbit torques in antiferromagnet/heavy metal heterostructures is an important first step towards this goal. Here, we employ magneto-optic techniques to study damping-like spin-orbit torque (DL-SOT) in a-plane $α$-Fe$_2$O$_3$ (hematite) with a Pt spin-orbit overlayer. We find that the DL-SOT efficiency is two orders of magnitude larger than reported in c- and r-plane hematite/Pt using harmonic Hall techniques. The large magnitude of DL-SOT is supported by direct imaging of current-induced motion of antiferromagnetic domains that happens at moderate current densities. Our study introduces a new method for quantifying spin-orbit torque in antiferromagnets with a small canted moment and identifies a-plane $α$-Fe$_2$O$_3$ as a promising candidate to realize efficient SOT switching.

cond-mat.mtrl-sci↗

arXiv2024

KITRO: Refining Human Mesh by 2D Clues and Kinematic-tree Rotation

2D keypoints are commonly used as an additional cue to refine estimated 3D human meshes. Current methods optimize the pose and shape parameters with a reprojection loss on the provided 2D keypoints. Such an approach, while simple and intuitive, has limited effectiveness because the optimal solution is hard to find in ambiguous parameter space and may sacrifice depth. Additionally, divergent gradients from distal joints complicate and deviate the refinement of proximal joints in the kinematic chain. To address these, we introduce Kinematic-Tree Rotation (KITRO), a novel mesh refinement strategy that explicitly models depth and human kinematic-tree structure. KITRO treats refinement from a bone-wise perspective. Unlike previous methods which perform gradient-based optimizations, our method calculates bone directions in closed form. By accounting for the 2D pose, bone length, and parent joint's depth, the calculation results in two possible directions for each child joint. We then use a decision tree to trace binary choices for all bones along the human skeleton's kinematic-tree to select the most probable hypothesis. Our experiments across various datasets and baseline models demonstrate that KITRO significantly improves 3D joint estimation accuracy and achieves an ideal 2D fit simultaneously. Our code available at: https://github.com/MartaYang/KITRO.

cs.CV↗

arXiv2024

Emergent Ferromagnetism at LaFeO3/SrTiO3 Interface Arising from Strain-induced Spin-State Transition

Creating new interfacial magnetic states with desired functionalities is attractive for fundamental studies and spintronics applications. The emergence of interfacial magnetic phases demands the fabrication of pristine interfaces and the characterization and understanding of atomic structure as well as electronic, magnetic, and orbital degrees of freedom at the interface. Here, we report a novel interfacial insulating ferromagnetic order in antiferromagnetic LaFeO3 grown on SrTiO3, characterized by a combination of electron microscopy and spectroscopy, magnetometry, and density functional theory. The epitaxial strain drives a spin-state disproportionation in the interfacial layer of LaFeO3, which leads to a checkerboard arrangement of low- and high-spin Fe3+ ions inside smaller and larger FeO6 octahedra, respectively. Ferromagnetism at the interface arises from superexchange interactions between the low- and high-spin Fe3+. The detailed understanding of creation of emergent magnetism illustrates the potential of designing and controlling orbital degrees of freedom at the interface to realize novel phases and functionalities for future spin-electronic applications.

cond-mat.mtrl-sci↗

arXiv2023

Single- and Multimagnon Dynamics in Antiferromagnetic $α$-Fe$_2$O$_3$ Thin Films

Understanding the spin dynamics in antiferromagnetic (AFM) thin films is fundamental for designing novel devices based on AFM magnon transport. Here, we study the magnon dynamics in thin films of AFM $S=5/2$ $α$-Fe$_2$O$_3$ by combining resonant inelastic x-ray scattering, Anderson impurity model plus dynamical mean-field theory, and Heisenberg spin model. Below 100 meV, we observe the thickness-independent (down to 15 nm) acoustic single-magnon mode. At higher energies (100-500 meV), an unexpected sequence of equally spaced, optical modes is resolved and ascribed to $ΔS_z = 1$, 2, 3, 4, and 5 magnetic excitations corresponding to multiple, noninteracting magnons. Our study unveils the energy, character, and momentum-dependence of single and multimagnons in $α$-Fe$_2$O$_3$ thin films, with impact on AFM magnon transport and its related phenomena. From a broader perspective, we generalize the use of L-edge resonant inelastic x-ray scattering as a multispin-excitation probe up to $ΔS_z = 2S$. Our analysis identifies the spin-orbital mixing in the valence shell as the key element for accessing excitations beyond $ΔS_z = 1$, and up to, e.g., $ΔS_z = 5$. At the same time, we elucidate the novel origin of the spin excitations beyond the $ΔS_z = 2$, emphasizing the key role played by the crystal lattice as a reservoir of angular momentum that complements the quanta carried by the absorbed and emitted photons.

cond-mat.str-el↗

arXiv2022

Strong On-Chip Microwave Photon-Magnon Coupling Using Ultra-low Damping Epitaxial Y3Fe5O12 Films at 2 Kelvin

Y3Fe5O12 is arguably the best magnetic material for magnonic quantum information science (QIS) because of its extremely low damping. We report ultralow damping at 2 K in epitaxial Y3Fe5O12 thin films grown on a diamagnetic Y3Sc2Ga3O12 substrate that contains no rare-earth elements. Using these ultralow damping YIG films, we demonstrate for the first time strong coupling between magnons in patterned YIG thin films and microwave photons in a superconducting Nb resonator. This result paves the road towards scalable hybrid quantum systems that integrate superconducting microwave resonators, YIG film magnon conduits, and superconducting qubits into on-chip QIS devices.

cond-mat.mtrl-sci↗

arXiv2022

Current-induced switching of thin film $α$-Fe$_2$O$_3$ devices imaged using a scanning single-spin microscope

Electrical switching of Néel order in an antiferromagnetic insulator is desirable as a basis for memory applications. Unlike electrically-driven switching of ferromagnetic order via spin-orbit torques, electrical switching of antiferromagnetic order remains poorly understood. Here we investigate the low-field magnetic properties of 30 nm thick, c-axis oriented $α$-Fe$_2$O$_3$ Hall devices using a diamond nitrogen-vacancy (NV) center scanning microscope. Using the canted moment of $α$-Fe$_2$O$_3$ as a magnetic handle on its Néel vector, we apply a saturating in-plane magnetic field to create a known initial state before letting the state relax in low field for magnetic imaging. We repeat this procedure for different in-plane orientations of the initialization field. We find that the magnetic field images are characterized by stronger magnetic textures for fields along $[\bar{1}\bar{1}20]$ and $[11\bar{2}0]$, suggesting that despite the expected 3-fold magneto-crystalline anisotropy, our $α$-Fe$_2$O$_3$ thin films have an overall in-plane uniaxial anisotropy. We also study current-induced switching of the magnetic order in $α$-Fe$_2$O$_3$. We find that the fraction of the device that switches depends on the current pulse duration, amplitude and direction relative to the initialization field. Specifically, we find that switching is most efficient when current is applied along the direction of the initialization field.

cond-mat.mtrl-sci↗

arXiv2022

Anisotropic Magnetoresistance and Nontrivial Spin Hall Magnetoresistance in Pt/$α$-Fe$_2$O$_3$ Bilayers

To date, magnetic proximity effect (MPE) has only been conclusively observed in ferromagnet (FM) based systems. We report the observation of anomalous Hall effect and anisotropic magnetoresistance in angular dependent magnetoresistance (ADMR) measurements in Pt on antiferromagnetic (AF) $α$-Fe$_2$O$_3$(0001) epitaxial films at 10 K, which provide evidence for the MPE. The Néel order of $α$-Fe$_2$O$_3$ and the induced magnetization in Pt show a unique ADMR compared with all other FM and AF systems. A macrospin response model is established and can explain the AF spin configuration and all main ADMR features in the Pt/$α$-Fe$_2$O$_3$ bilayers.

cond-mat.mtrl-sci↗

arXiv2022

Electrical Switching of Tristate Antiferromagnetic Néel Order in $α$-Fe$_{2}$O$_{3}$ Epitaxial Films

The ability to manipulate antiferromagnetic (AF) moments is a key requirement for the emerging field of antiferromagnetic spintronics. Electrical switching of bi-state AF moments has been demonstrated in metallic AFs, CuMnAs and Mn$_2$Au. Recently, current-induced "saw-tooth" shaped Hall resistance was reported in Pt/NiO bilayers, while its mechanism is under debate. Here, we report the first demonstration of convincing, non-decaying, step-like electrical switching of tri-state Néel order in Pt/$α$-Fe$_2$O$_3$ bilayers. Our experimental data, together with Monte-Carlo simulations, reveal the clear mechanism of the switching behavior of $α$-Fe$_2$O$_3$ Néel order among three stable states. We also show that the observed "saw-tooth" Hall resistance is due to an artifact of Pt, not AF switching, while the signature of AF switching is step-like Hall signals. This demonstration of electrical control of magnetic moments in AF insulator (AFI) films will greatly expand the scope of AF spintronics by leveraging the large family of AFIs.

cond-mat.mes-hall↗