Showing 1–50 of 113 results for author: Zhu, M

Experimental Realization of Thermal Reservoirs with Tunable Temperature in a Trapped-Ion Spin-Boson Simulator

Authors: Visal So, Mingjian Zhu, Midhuna Duraisamy Suganthi, Abhishek Menon, George Tomaras, Roman Zhuravel, Han Pu, Guido Pagano

Abstract: We propose and demonstrate an experimental scheme to engineer thermal baths with independently tunable temperatures and dissipation rates for the motional modes of a trapped-ion system. This approach enables robust thermal-state preparation and quantum simulations of open-system dynamics in bosonic and spin-boson models at well-controlled finite temperatures. We benchmark our protocol by experimen… ▽ More We propose and demonstrate an experimental scheme to engineer thermal baths with independently tunable temperatures and dissipation rates for the motional modes of a trapped-ion system. This approach enables robust thermal-state preparation and quantum simulations of open-system dynamics in bosonic and spin-boson models at well-controlled finite temperatures. We benchmark our protocol by experimentally realizing out-of-equilibrium dynamics of a charge-transfer model at different temperatures. We observe that, when the process occurs at a higher temperature, the transfer rate spectrum broadens, with reduced rates at small donor-acceptor energy gaps and enhanced rates at large gaps. We then employ our scheme to study local-temperature effects in a two-mode vibrationally assisted exciton transfer system, where we observe thermally activated interference pathways for excitation transfer. △ Less

Submitted 11 November, 2025; originally announced November 2025.

Comments: 7 + 2 + 5 pages, 4 + 4 + 5 figures

Non-altermagnetic spin texture in MnTe

Authors: Meng Zeng, Pengfei Liu, Ming-Yuan Zhu, Naifu Zheng, Xiang-Rui Liu, Yu-Peng Zhu, Tian-Hao Shao, Yu-Jie Hao, Xiao-Ming Ma, Gexing Qu, Rafał Kurleto, Dawid Wutke, Rong-Hao Luo, Yue Dai, Xiaoqian Zhang, Koji Miyamoto, Kenya Shimada, Taichi Okuda, Kiyohisa Tanaka, Yaobo Huang, Qihang Liu, Chang Liu

Abstract: Recently, altermagnets have emerged as promising candidates in spintronics, uniquely combining large spin-polarized electronic states with zero net magnetization. A prominent example is $α$-MnTe, whose altermagnetic spin splitting, i.e., the degeneracy lift in momentum space induced by collinear magnetic order, has been experimentally observed. However, the direct evidence of its $g$-wave spin pol… ▽ More Recently, altermagnets have emerged as promising candidates in spintronics, uniquely combining large spin-polarized electronic states with zero net magnetization. A prominent example is $α$-MnTe, whose altermagnetic spin splitting, i.e., the degeneracy lift in momentum space induced by collinear magnetic order, has been experimentally observed. However, the direct evidence of its $g$-wave spin polarization, the key property for altermagnetic spintronics, is thus far lacking. By combining high-resolution spin- and angle-resolved photoemission spectroscopy (SARPES) with first-principles calculations, we reveal a $k_z$-independent, Rashba-like spin texture in $α$-MnTe. Our results indicate that the observed spin polarization is primarily governed by spin-orbit coupling, whereas the magnetic order contributes to the splitting of energy bands but plays a much less dominant role in spin polarization due to the multi-domain nature. From this result, we further establish a way to prescreen altermagnet candidates that favor the formation of large antiferromagnetic domains based on symmetry analysis. Our work elucidates the interplay between magnetic order and spin-orbit coupling in governing spin polarization in altermagnet candidates, and thereby advances the materials design paradigm for spin-functional devices. △ Less

Submitted 4 November, 2025; originally announced November 2025.

Comments: 19 pages, 4 figures

Longitudinal transport spin polarization of spin degenerate antiferromagnets

Authors: Meng Zhu, Jianting Dong, Xinlu Li, Jiahao Shentu, Yizhuo Song, Evgeny Y. Tsymbal, Jia Zhang

Abstract: A vital goal in spintronics is the efficient electrical generation of spin currents, a pursuit that has recently focused on using antiferromagnets (AFMs) as spin current sources. It has been demonstrated that antiferromagnets with broken PT symmetry (parity + time reversal) can efficiently generate longitudinal and transverse spin currents. At the same time, it has been generally thought that anti… ▽ More A vital goal in spintronics is the efficient electrical generation of spin currents, a pursuit that has recently focused on using antiferromagnets (AFMs) as spin current sources. It has been demonstrated that antiferromagnets with broken PT symmetry (parity + time reversal) can efficiently generate longitudinal and transverse spin currents. At the same time, it has been generally thought that antiferromagnets with PT symmetry (PT-AFMs) forbid the longitudinal spin polarization due to their spin-degenerate band structure. Here, in contrast to this common expectation, we show, using theoretical analysis based on magnetic point group symmetry, that most PT-AFMs can generate longitudinal spin currents due to spin-orbit coupling. Using density-functional theory, we calculate the longitudinal spin conductivity of representative PT-AFMs, L10-MnPt and Mn2Au, and show that its magnitude is comparable to that of their PT-broken counterparts. Our symmetry-enabled classification of antiferromagnets and theoretical results for the longitudinal spin conductivity in representative PT-AFMs expands our understanding of spin transport and shows the possibility of robust spin-current generation in a broad range of spin-degenerate antiferromagnets. △ Less

Submitted 5 October, 2025; originally announced October 2025.

Probing the Critical Point (CritPt) of AI Reasoning: a Frontier Physics Research Benchmark

Authors: Minhui Zhu, Minyang Tian, Xiaocheng Yang, Tianci Zhou, Lifan Yuan, Penghao Zhu, Eli Chertkov, Shengyan Liu, Yufeng Du, Ziming Ji, Indranil Das, Junyi Cao, Yufeng Du, Jiabin Yu, Peixue Wu, Jinchen He, Yifan Su, Yikun Jiang, Yujie Zhang, Chang Liu, Ze-Min Huang, Weizhen Jia, Yunkai Wang, Farshid Jafarpour, Yong Zhao , et al. (39 additional authors not shown)

Abstract: While large language models (LLMs) with reasoning capabilities are progressing rapidly on high-school math competitions and coding, can they reason effectively through complex, open-ended challenges found in frontier physics research? And crucially, what kinds of reasoning tasks do physicists want LLMs to assist with? To address these questions, we present the CritPt (Complex Research using Integr… ▽ More While large language models (LLMs) with reasoning capabilities are progressing rapidly on high-school math competitions and coding, can they reason effectively through complex, open-ended challenges found in frontier physics research? And crucially, what kinds of reasoning tasks do physicists want LLMs to assist with? To address these questions, we present the CritPt (Complex Research using Integrated Thinking - Physics Test, pronounced "critical point"), the first benchmark designed to test LLMs on unpublished, research-level reasoning tasks that broadly covers modern physics research areas, including condensed matter, quantum physics, atomic, molecular & optical physics, astrophysics, high energy physics, mathematical physics, statistical physics, nuclear physics, nonlinear dynamics, fluid dynamics and biophysics. CritPt consists of 71 composite research challenges designed to simulate full-scale research projects at the entry level, which are also decomposed to 190 simpler checkpoint tasks for more fine-grained insights. All problems are newly created by 50+ active physics researchers based on their own research. Every problem is hand-curated to admit a guess-resistant and machine-verifiable answer and is evaluated by an automated grading pipeline heavily customized for advanced physics-specific output formats. We find that while current state-of-the-art LLMs show early promise on isolated checkpoints, they remain far from being able to reliably solve full research-scale challenges: the best average accuracy among base models is only 5.7%, achieved by GPT-5 (high), moderately rising to around 10% when equipped with coding tools. Through the realistic yet standardized evaluation offered by CritPt, we highlight a large disconnect between current model capabilities and realistic physics research demands, offering a foundation to guide the development of scientifically grounded AI tools. △ Less

Submitted 20 November, 2025; v1 submitted 30 September, 2025; originally announced September 2025.

Comments: 39 pages, 6 figures, 6 tables

Direct determination of antiferroelectric-to-ferroelectric phase transition pathways in PbZrO$_3$ with Operando Electron Microscopy

Authors: Menglin Zhu, Michael Xu, Louis Alaerts, Hao Pan, Colin Gilgenbach, Geoffroy Hautier, Lane W. Martin, James M. LeBeau

Abstract: Under a sufficiently high applied electric field, a non-polar antiferroelectric material, such as \ce{PbZrO3}, can undergo a rapid transformation to a polar ferroelectric phase. While this behavior is promising for energy storage and electromechanical applications, a complete understanding of the atomic-scale mechanisms governing the phase transition remain elusive. Here, we employ \textit{operand… ▽ More Under a sufficiently high applied electric field, a non-polar antiferroelectric material, such as \ce{PbZrO3}, can undergo a rapid transformation to a polar ferroelectric phase. While this behavior is promising for energy storage and electromechanical applications, a complete understanding of the atomic-scale mechanisms governing the phase transition remain elusive. Here, we employ \textit{operando} scanning transmission electron microscopy electric field biasing to directly resolve the antiferroelectric-to-ferroelectric transition pathway in \ce{PbZrO3} thin films under device-relevant conditions. Atomic-resolution imaging reveals a multi-step transition that includes several metastable phases. Complementary nano-beam electron diffraction and atomic scale analysis further show that this pathway and its end states can be modulated, leading to the formation of a \quotes{dead layer} near the substrate with suppressed switching behavior. Taking advantage of this depth-dependent heterogeneity, dynamic phase transformations are observed between coexisting antiferroelectric and metastable ferroelectric phases. At this dynamic transition front, repeated phase interconversion is shown to be driven by competing internal (due to substrate clamping and extended defects) and external fields, allowing the relative energies of intermediate phases to be compared as a function of electric field. This work highlights the critical role of local energetics in phase stability and provides key experimental insights into field-induced phase transitions, guiding the design of antiferroelectric-based devices. △ Less

Submitted 8 September, 2025; originally announced September 2025.

Nonperturbative Semiclassical Spin Dynamics for Ordered Quantum Magnets

Authors: Hao Zhang, Tianyue Huang, Allen O. Scheie, Mengze Zhu, Tao Xie, N. Murai, S. Ohira-Kawamura, Andrey Zheludev, Andreas M. Läuchli, Cristian D. Batista

Abstract: In ordered quantum magnets where interactions between elementary excitations dominate over their kinetic energy, perturbative approaches often fail, making non-perturbative methods essential to capture spectral features such as bound states and the redistribution of weight within excitation continua. Although an increasing number of experiments report anomalous spin excitation continua in such sys… ▽ More In ordered quantum magnets where interactions between elementary excitations dominate over their kinetic energy, perturbative approaches often fail, making non-perturbative methods essential to capture spectral features such as bound states and the redistribution of weight within excitation continua. Although an increasing number of experiments report anomalous spin excitation continua in such systems, their microscopic interpretation remains an open challenge. Here, we investigate the spin dynamics of the triangular-lattice antiferromagnet in its 1/3-plateau phase using two complementary non-perturbative approaches: exact diagonalization in a truncated Hilbert space for a gas of elementary excitations (THED) and matrix product state (MPS) simulations. Alongside cross-validation between these methods, we benchmark our results against inelastic neutron scattering (INS) data. The THED analysis confirms the presence of two-magnon bound states and identifies the anomalous scattering continuum observed in both MPS and INS as a two-magnon resonance, arising from hybridization between the bound state and the two-magnon continuum. Furthermore, THED reveals bound states overlapping with the continuum, enriching the interpretation of continuum anomalies. More broadly, THED provides a robust framework for investigating anomalous spin excitation continua and bound-state effects in other materials with gapped spectra. Its combination of accuracy and computational efficiency makes it a powerful tool for extracting reliable microscopic models in semiclassical regimes. △ Less

Submitted 28 August, 2025; originally announced August 2025.

Comments: 9 + 14 pages, 5 + 12 figures

Operando Electron Microscopy of Nanoscale Electronic Devices on Non-Conductive Substrates

Authors: Menglin Zhu, Michael Xu, Zishen Tian, Colin Gilgenbach, Daniel Drury, Bridget R. Denzer, Ching-Che Lin, Deokyoung Kang, Lane W. Martin, James M. LeBeau

Abstract: Achieving operating conditions comparable to ``bulk'' electronic devices, such as thin film capacitors, during \textit{operando} electron microscopy remains challenging, particularly when devices are grown on non-conductive substrates. Limited precision of focused ion beam milling for sample preparation often necessitates the use of conductive substrates or artificially thick layers that differ fr… ▽ More Achieving operating conditions comparable to ``bulk'' electronic devices, such as thin film capacitors, during \textit{operando} electron microscopy remains challenging, particularly when devices are grown on non-conductive substrates. Limited precision of focused ion beam milling for sample preparation often necessitates the use of conductive substrates or artificially thick layers that differ from actual device architectures. These modifications can alter native strain, electrostatic boundary conditions, and ultimately device response. Here, we present a generic and versatile workflow for \textit{operando} biasing of thin-film capacitors in the (scanning) transmission electron microscope, including sample fabrication and device operation. By introducing a patterned insulating barrier adjacent to the bulk-characterized capacitors, our approach enables sample preparation without altering the original film structure. As a case study, we apply the method to a piezoelectric thin-film capacitor grown on an insulating substrate, and demonstrate that it preserves the boundary-condition-sensitive domain switching at the atomic scale under applied electric fields. Overall, the process can help to establish a foundation for systematic \textit{operando} studies of complex thin-film systems under representative bulk testing geometries. △ Less

Submitted 17 August, 2025; originally announced August 2025.

The doping evolution of the charge density wave and charge density fluctuations in La$_{2-x}$Sr$_x$CuO$_4$

Authors: Charles C. Tam, Mengze Zhu, Maud C. Barthélemy, Lauren J. Cane, Oliver J. Lipscombe, Stefano Agrestini, Jaewon Choi, Mirian Garcia-Fernandez, Ke-Jin Zhou, Stephen M. Hayden

Abstract: Cuprate superconductors show various collective charge correlations that are intimately connected with their electronic properties. In particular, charge order in the form of an incommensurate charge density wave (CDW) order with an in-plane wavevector $δ_{\text{CDW}} \approx $ 0.23--0.35~r.l.u. appears to be universally present. In addition to CDW, dynamic charge density fluctuations (CDF) are al… ▽ More Cuprate superconductors show various collective charge correlations that are intimately connected with their electronic properties. In particular, charge order in the form of an incommensurate charge density wave (CDW) order with an in-plane wavevector $δ_{\text{CDW}} \approx $ 0.23--0.35~r.l.u. appears to be universally present. In addition to CDW, dynamic charge density fluctuations (CDF) are also present with wavevectors comparable to $δ_{\text{CDW}}$. CDFs are present up to $\sim300\;$K and have relatively short correlation lengths of $ξ\sim 20$\;Å. Here we use Cu-$L_3$ and O-$K$ resonant inelastic X-ray scattering (RIXS) to study the doping dependence of CDW and CDFs in La$_{2-x}$Sr$_x$CuO$_4$. We fit our data with (quasi)elastic peaks resulting from the CDW and up to four inelastic modes associated with oxygen phonons that can be strongly coupled to the CDFs. Our analysis allows us to separate the charge correlations into three components: the CDW with wavevector $δ_{4a-\text{CDW}} \approx 0.24$ and two CDF components with $δ_{4a-\text{CDF}} \approx 0.24$ and $δ_{3a-\text{CDF}} \approx 0.30$. We find that for $T \approx T_c$ the CDW coexists with the CDFs for dopings near $x=p \sim 1/8$. The $4a$-CDW disappears beyond $x=0.16$ and the $4a$-CDF beyond $x=0.19$, leaving only a weak $3a$-CDF at the highest doping studied, $x=0.22$. Our data suggest that low-energy charge fluctuations exist up to doping $x=0.19=p^{\star}$, where the pseudogap disappears, however, we find no evidence that they are associated with a quantum critical point. △ Less

Submitted 12 August, 2025; originally announced August 2025.

Spin-flop-like transition as quantum critical point in Cs$_2$RuO$_4$

Authors: S. D. Nabi, M. Zhu, K. Yu. Povarov, D. G. Mazzone, J. Lass, Y. Wu, Z. Yan, S. Gvasaliya, A. Zheludev

Abstract: We report thermodynamic, neutron diffraction, and inelastic neutron scattering measurements on Cs$_2$RuO$_4$, a member of the celebrated family of frustrated magnets Cs$_2$MX$_4$ (M = Cu, Co, X = Br, Cl). Unlike the previously studied members, it is based on $4d$ transition metal ions with $S=1$. Mapping out the $H-T$ magnetic phase diagram reveals an unusual continuous spin-flop-like phase transi… ▽ More We report thermodynamic, neutron diffraction, and inelastic neutron scattering measurements on Cs$_2$RuO$_4$, a member of the celebrated family of frustrated magnets Cs$_2$MX$_4$ (M = Cu, Co, X = Br, Cl). Unlike the previously studied members, it is based on $4d$ transition metal ions with $S=1$. Mapping out the $H-T$ magnetic phase diagram reveals an unusual continuous spin-flop-like phase transition associated with a quantum critical point within the antiferromagnetically ordered phase. A quantitative analysis of the complex magnetic excitation spectrum measured in zero field allows us to derive a model magnetic Hamiltonian for this compound. Its main feature is a frustration of magnetic anisotropy on a level that is much higher than in any of the previously studied species. This frustration naturally explains the peculiar phase transition observed. △ Less

Submitted 21 October, 2025; v1 submitted 26 July, 2025; originally announced July 2025.

Comments: 12 pages, 12 figures

Journal ref: Phys. Rev. B 112, 134436 (2025)

Quantum Simulation of Charge and Exciton Transfer in Multi-mode Models using Engineered Reservoirs

Authors: Visal So, Midhuna Duraisamy Suganthi, Mingjian Zhu, Abhishek Menon, George Tomaras, Roman Zhuravel, Han Pu, Peter G. Wolynes, José N. Onuchic, Guido Pagano

Abstract: Quantum simulation offers a route to study open-system molecular dynamics in non-perturbative regimes by programming the interactions among electronic, vibrational, and environmental degrees of freedom on similar energy scales. Trapped-ion systems possess this capability, with their native spins, phonons, and tunable dissipation integrated within a single platform. Here, we demonstrate an open-sys… ▽ More Quantum simulation offers a route to study open-system molecular dynamics in non-perturbative regimes by programming the interactions among electronic, vibrational, and environmental degrees of freedom on similar energy scales. Trapped-ion systems possess this capability, with their native spins, phonons, and tunable dissipation integrated within a single platform. Here, we demonstrate an open-system quantum simulation of charge and exciton transfer in a multi-mode linear vibronic coupling model. Employing tailored spin-phonon interactions alongside reservoir engineering techniques, we emulate a system with two dissipative vibrational modes coupled to donor and acceptor electronic sites and follow its non-equilibrium dynamics. We continuously tune the system from the charge transfer (CT) regime to the vibrationally assisted exciton transfer (VAET) regime by controlling the vibronic coupling strengths. We find that degenerate modes enhance CT and VAET rates at large energy gaps, while non-degenerate modes activate slow-mode pathways that reduce the energy-gap dependence, thus enlarging the window for efficient transfer. These results show that the presence of one additional vibration introduces interfering vibrationally assisted pathways and reshapes non-perturbative quantum excitation transfer. Our work establishes a scalable and hardware-efficient route to simulating chemically relevant, many-mode vibronic processes with engineered environments, guiding the design of next-generation organic photovoltaics and molecular electronics. △ Less

Submitted 15 September, 2025; v1 submitted 28 May, 2025; originally announced May 2025.

Comments: 10 + 8 pages, 5 + 7 figures, 1 table

phaser: A unified and extensible framework for fast electron ptychography

Authors: Colin Gilgenbach, Menglin Zhu, James M. LeBeau

Abstract: We present \code{phaser}, an open-source Python package that provides a unified interface to both conventional and gradient descent-based ptychographic algorithms. Features such as mixed-state probe, probe position correction, and multislice ptychography make experimental reconstructions practical and robust. Reconstructions are specified in a declarative format and can be run from a command line,… ▽ More We present \code{phaser}, an open-source Python package that provides a unified interface to both conventional and gradient descent-based ptychographic algorithms. Features such as mixed-state probe, probe position correction, and multislice ptychography make experimental reconstructions practical and robust. Reconstructions are specified in a declarative format and can be run from a command line, Jupyter notebook, or web interface. Multiple computational backends are supported to provide maximum flexibility. With the JAX computational backend, a six-fold improvement in iteration speed is achieved over a widely used package implemented in MATLAB, fold\_slice/PtychoShelves. We report reconstruction success for a variety of experimental datasets, and detail the effects of regularization on convergence and reconstruction quality. The software promises to speed the application and development of ptychographic methods for materials science. △ Less

Submitted 17 July, 2025; v1 submitted 20 May, 2025; originally announced May 2025.

General Phase Segregation and Phase Pinning Effects in Ln-doped Lead Halide Perovskite with Dual-wavelength Lasing

Authors: Junyu He, Jun Luo, Weihao Zheng, Biyuan Zheng, Mengjian Zhu, Jiahao Liu, Tingzhao Fu, Jing Wu, Zhihong Zhu, Fang Wang, Xiujuan Zhuang

Abstract: Lead halide perovskites (LHPs) exhibit outstanding optoelectronic properties, making them highly promising for applications in various optoelectronics devices. However, rapid ion migration in LHPs not only undermines device stability but also hinders the development of multi-band composite structures, which are crucial to advancing perovskite bandgap engineering and unlocking novel applications. H… ▽ More Lead halide perovskites (LHPs) exhibit outstanding optoelectronic properties, making them highly promising for applications in various optoelectronics devices. However, rapid ion migration in LHPs not only undermines device stability but also hinders the development of multi-band composite structures, which are crucial to advancing perovskite bandgap engineering and unlocking novel applications. Here, we introduce a novel and general strategy involving both phase segregation and phase pinning by doping Er$^{3+}$ into CsPb(X$_x$Y$_{1-x}$)$_3$ (X, Y = Cl, Br, I) microplates via a simple one-step chemical vapor deposition method. The ion migration is effectively suppressed and a variety of stable multi-band composite structures are demonstrated, with diverse dual-band photoluminescence emissions covering the red, green, and blue spectral bands. The corresponding high-performance dual-wavelength lasers have also been fabricated, confirming the stability and high crystalline quality of these multi-band composite structures. In addition, this strategy is extended to the doping of various lanthanide ion and the incorporation of different mixed halides into LHPs. As a result, a series of multi-band composite structures based on LHPs and corresponding dual-wavelength lasers are developed, thereby validating the generality of this strategy. Theoretical calculations clarify the phase segregation and phase pinning mechanism in these LHPs. Our work not only facilitates the stability design of LHPs but also significantly advances the bandgap engineering, thereby contributing to the expansion of their potential applications in the optoelectronic future. △ Less

Submitted 18 April, 2025; originally announced April 2025.

Comments: 22 pages, 5 figures

Hallmarks of terahertz magnon currents in an antiferromagnetic insulator

Authors: Hongsong Qiu, Oliver Franke, Yuanzhe Tian, Zdeněk Kašpar, Reza Rouzegar, Oliver Gueckstock, Ji Wu, Maguang Zhu, Biaobing Jin, Yongbing Xu, Tom S. Seifert, Di Wu, Piet W. Brouwer, Tobias Kampfrath

Abstract: The efficient transport of spin angular momentum is expected to play a crucial role in future spintronic devices, which potentially operate at frequencies reaching the terahertz range. Antiferromagnetic insulators exhibit significant potential for facilitating ultrafast pure spin currents by terahertz magnons. Consequently, we here use femtosecond laser pulses to trigger ultrafast spin currents ac… ▽ More The efficient transport of spin angular momentum is expected to play a crucial role in future spintronic devices, which potentially operate at frequencies reaching the terahertz range. Antiferromagnetic insulators exhibit significant potential for facilitating ultrafast pure spin currents by terahertz magnons. Consequently, we here use femtosecond laser pulses to trigger ultrafast spin currents across antiferromagnetic NiO thin films in Py|NiO|Pt stacks, where permalloy (Py) and Pt serve as spin-current source and detector respectively. We find that the spin current pulses traversing NiO reach a velocity up to 40 nm/ps and experience increasing delay and broadening as the NiO thickness is increased. We can consistently explain our observations by ballistic transport of incoherent magnon. Our approach has high potential to characterize terahertz magnon transport in magnetic insulators with any kind of magnetic order. △ Less

Submitted 10 April, 2025; originally announced April 2025.

Probing Rate-Dependent Liquid Shear Viscosity Using Combined Machine Learning and Non-Equilibrium Molecular Dynamics

Authors: Hongyu Gao, Minghe Zhu, Jia Ma, Marc Honecker, Kexian Li

Abstract: Accurately measuring liquid dynamic viscosity across a wide range of shear rates, from the linear-response to shear-thinning regimes, presents significant experimental challenges due to limitations in resolving high shear rates and controlling thermal effects. In this study, we integrated machine learning (ML) with non-equilibrium molecular dynamics (NEMD) simulations to address these challenges.… ▽ More Accurately measuring liquid dynamic viscosity across a wide range of shear rates, from the linear-response to shear-thinning regimes, presents significant experimental challenges due to limitations in resolving high shear rates and controlling thermal effects. In this study, we integrated machine learning (ML) with non-equilibrium molecular dynamics (NEMD) simulations to address these challenges. A supervised artificial neural network (ANN) model was developed to predict viscosity as a function of shear rate, normal pressure, and temperature, effectively capturing the complex interplay among these variables. The model reveals distinct trends in shear viscosity, characterized by the shear-thinning exponent, and highlights non-monotonic behavior in the radius of gyration components, reflecting molecular morphological changes driven by rate-dependent volume expansion. Notably, temperature effects diminish at higher shear rates, where molecular alignment and spacing dominate the response to shear. By implementing the 'fix npt/sllod' command in LAMMPS, we achieve precise constant-pressure control in NEMD simulations, ensuring accurate representation of system dynamics. This study demonstrates the potential of ML-enhanced NEMD for efficient and accurate viscosity prediction, providing a robust framework for future research in complex fluid dynamics and material design. △ Less

Submitted 25 March, 2025; originally announced March 2025.

Critical spin fluctuations across the superconducting dome in La$_{2-x}$Sr$_{x}$CuO$_4$

Authors: Jacopo Radaelli, Oliver J. Lipscombe, Mengze Zhu, J. Ross Stewart, Aavishkar A. Patel, Subir Sachdev, Stephen M. Hayden

Abstract: Overdoped cuprate superconductors are strange metals above their superconducting transition temperature. In such materials, the electrical resistivity has a strong linear dependence on temperature ($T$) and electrical current is not carried by electron quasiparticles as in conventional metals. Here we demonstrate that the strange metal behaviour co-exists with strongly temperature-dependent critic… ▽ More Overdoped cuprate superconductors are strange metals above their superconducting transition temperature. In such materials, the electrical resistivity has a strong linear dependence on temperature ($T$) and electrical current is not carried by electron quasiparticles as in conventional metals. Here we demonstrate that the strange metal behaviour co-exists with strongly temperature-dependent critical spin fluctuations showing dynamical scaling across the cuprate phase diagram. Our neutron scattering observations and the strange metal behaviour are consistent with a spin density wave quantum phase transition in a metal with spatial disorder in the tuning parameter. Numerical computations using a theory of spin density waves in a disordered metal yield an extended `Griffiths phase' with scaling properties in agreement with experimental observations. Thus we establish that low-energy spin excitations and spatial disorder are central to the strange metal behaviour. △ Less

Submitted 26 November, 2025; v1 submitted 17 March, 2025; originally announced March 2025.

Inefficiency of orbital Hall effect on the spin torque in transition metal/ferromagnet bilayers

Authors: Yizhuo Song, Jialin Tian, Fanxing Zheng, Jianting Dong, Meng Zhu, Jia Zhang

Abstract: Current induced spin torque is essential and crucial in spintronics. In this work, we systematically investigate the spin torque in transition metal(TM)/ferromagnet(FM) bilayers by using first-principles calculations and taking into account the phonon scattering at room temperature. To examine the spin and orbital Hall contribution, the studied transition metals include 5d heavy metals Pt, W, Au a… ▽ More Current induced spin torque is essential and crucial in spintronics. In this work, we systematically investigate the spin torque in transition metal(TM)/ferromagnet(FM) bilayers by using first-principles calculations and taking into account the phonon scattering at room temperature. To examine the spin and orbital Hall contribution, the studied transition metals include 5d heavy metals Pt, W, Au as well as 3d light metals Ti, V, Cr, Cu etc. We found that in TM/CoFe bilayers with typical 3d and 5d transition metals, the spin torque on CoFe mainly originates from spin Hall mechanism with the magnitude and sign of damping like torque efficiency consistent with the spin Hall conductivity. In TM/Ni bilayers, the spin torque is contributed by three mechanisms including spin and orbital Hall current in TM, as well as self-torque in Ni. The orbital Hall contribution in TM is accompanied by noteworthy opposite self spin torque in Ni, which leads to inapparent torque efficiency in Ti/Ni and V/Ni bilayers. For TM(5d heavy metal)/Ni bilayers, the spin torque induced by orbital Hall and self-torque in Ni nearly cancel each other, which makes the spin torque on Ni still align with that of the spin Hall effect in TM. Our work reveals much less efficient contribution of orbital Hall than spin Hall effect on the spin torque in transition metal/ferromagnet bilayers. △ Less

Submitted 28 March, 2025; v1 submitted 2 March, 2025; originally announced March 2025.

Abnormal Normal State and Pressure-driven Reentrant Superconductivity in the Heavy $d$-electron Superconductor Rh$_{17}$S$_{15}$

Authors: Xiaofeng Xu, J. Y. Nie, C. Q. Xu, Z. M. Zhu, Xiangzhuo Xing, Y. L. Huang, C. T. Zhang, N. Zuo, C. C. Zhao, Z. Y. Zhang, W. Zhou, W. H. Jiao, S. Xu, Q. Zhang, Zhu-An Xu, X. B. Liu, Dong Qian, Shiyan Li

Abstract: Superconductivity beyond the conventional Bardeen-Cooper-Schrieffer (BCS) framework often emerges out of a normal state that is accompanied by exotic magnetism and thereby displays many exceptional transport and thermodynamic properties. Here we report that the normal state of the heavy $d$-electron superconductor Rh$_{17}$S$_{15}$ is characterized by a weak \textit{ferromagnetism} that persists u… ▽ More Superconductivity beyond the conventional Bardeen-Cooper-Schrieffer (BCS) framework often emerges out of a normal state that is accompanied by exotic magnetism and thereby displays many exceptional transport and thermodynamic properties. Here we report that the normal state of the heavy $d$-electron superconductor Rh$_{17}$S$_{15}$ is characterized by a weak \textit{ferromagnetism} that persists up to room temperature. We show that the broad hump in its resistivity likely results from the Kondo interaction of the conduction electrons with this novel magnetism. By applying pressure, superconductivity is fully suppressed first. In the high-pressure regime, however, we observe a second dome of superconductivity with its maximum $T_c$ greater than the ambient pressure value, highlighting the possible \textit{unconventional} superconductivity in this heavy $d$-electron sulfide. △ Less

Submitted 17 February, 2025; originally announced February 2025.

Comments: 4 figures

Journal ref: Phys. Rev. B 111, L161113 (2025)

Hedgehog-like spin texture in Sb-doped MnBi$_2$Te$_4$

Authors: Meng Zeng, Shu Mo, Ke Zhang, Yu-Jie Hao, Yu-Peng Zhu, Xiang-Rui Liu, Cheng Zhang, Ming-Yuan Zhu, Shiv Kumar, Takuma Iwata, Koji Miyamoto, Taichi Okuda, Kenya Shimada, Kenta Kuroda, Xiao-Ming Ma, Chang Liu

Abstract: We employ spin- and angle-resolved photoemission spectroscopy and circular-dichroism ARPES to systematically investigate the spin texture of Sb-doped MnBi$_2$Te$_4$. Our results display a hedgehog-like spin texture in this system which is signified by reversed-orienting out-of-plane spins at the Dirac gap. Our finding reveals the presence of time-reversal symmetry breaking, implying the possibilit… ▽ More We employ spin- and angle-resolved photoemission spectroscopy and circular-dichroism ARPES to systematically investigate the spin texture of Sb-doped MnBi$_2$Te$_4$. Our results display a hedgehog-like spin texture in this system which is signified by reversed-orienting out-of-plane spins at the Dirac gap. Our finding reveals the presence of time-reversal symmetry breaking, implying the possibility for realization of high-temperature quantum anomalous Hall effect. △ Less

Submitted 10 February, 2025; originally announced February 2025.

Comments: 12 pages, 4 figures

Journal ref: Phys. Rev. Research 7, L032021 (2025)

Nonrelativistic spin-splitting multiferroic antiferromagnet and compensated ferrimagnet with zero net magnetization

Authors: Jianting Dong, Kun Wu, Meng Zhu, Fanxing Zheng, Xinlu Li, Jia Zhang

Abstract: Spin-splitting antiferromagnets with spin-polarized band structures in momentum space have garnered intensive research attention due to their zero net magnetic moments, ultras fast spin dynamics as conventional antiferromagnets, and spin-polarized transport properties akin to ferromagnets, making them promising candidates for antiferromagnetic spintronics. However, unlike spin-torque switching of… ▽ More Spin-splitting antiferromagnets with spin-polarized band structures in momentum space have garnered intensive research attention due to their zero net magnetic moments, ultras fast spin dynamics as conventional antiferromagnets, and spin-polarized transport properties akin to ferromagnets, making them promising candidates for antiferromagnetic spintronics. However, unlike spin-torque switching of ferromagnets by electric current, efficient electric control of spin-splitting antiferromagnetic order remains challenges. In this work, we identify prototypes of multiferroic spin-splitting antiferromagnets, including BiFeO3, Fe2Mo3O8 and compensated ferrimagnet GaFeO3 with ferroelectric polarization as well as spin-polarized electronic structures. We establish design principles for the spin-splitting multiferroic antiferromagnets and compensated ferrimagnets, elucidating the band symmetry features in Brillouin zone. We demonstrate that the spin polarization in spin-splitting magnets, despite of zero net magnetic moment, can be switched by ferroelectric polarization, providing an efficient means of controlling the antiferromagnetic order. Our work may inspire future development of novel multiferroic functional magnets with zero magnetic moments and pave the way for their applications in magnetoelectric spintronic devices. △ Less

Submitted 6 January, 2025; originally announced January 2025.

Spin Hall effect in 3d ferromagnetic metals for field-free switching of perpendicular magnetization: A first-principles investigation

Authors: Fanxing Zheng, Jianting Dong, Yizhuo Song, Meng Zhu, Xinlu Li, Jia Zhang

Abstract: Ferromagnetic metals, with the potential to generate spin current with unconventional spin polarization via the spin Hall effect, offer promising opportunities for field-free switching of perpendicular magnetization and for the spin-orbit torque devices. In this study, we investigate two distinct spin Hall mechanisms in 3d ferromagnetic metals including spin-orbit coupling driven spin Hall effect… ▽ More Ferromagnetic metals, with the potential to generate spin current with unconventional spin polarization via the spin Hall effect, offer promising opportunities for field-free switching of perpendicular magnetization and for the spin-orbit torque devices. In this study, we investigate two distinct spin Hall mechanisms in 3d ferromagnetic metals including spin-orbit coupling driven spin Hall effect in Fe, Co, Ni and their alloys, and non-relativistic spin Hall effect arising from anisotropic spin-polarized transport by taking L10-MnAl as an example. By employing first-principles calculations, we examine the temperature and alloy composition dependence of spin Hall conductivity in Fe, Co, Ni and their alloys. Our results reveal that the spin Hall conductivities with out-of-plane spin polarization in 3d ferromagnetic metals are at the order of 1000 \frac{\hbar}{2e} \left( Ω\, \text{cm} \right)^{-1} at 300 K, but with a relatively low spin Hall angles around 0.01~0.02 due to the large longitudinal conductivity. For L10-MnAl(101), the non-relativistic spin Hall conductivity can reach up to 10000\frac{\hbar}{2e} \left( Ω\, \text{cm} \right)^{-1}, with a giant spin Hall angle around 0.25 at room temperature. By analyzing the magnetization switching process, we demonstrate deterministic switching of perpendicular magnetization without an external magnetic field by using 3d ferromagnetic metals as spin current sources. Our work may provide an unambiguous understanding on spin Hall effect in ferromagnetic metals and pave the way for their potential applications in related spintronic devices. △ Less

Submitted 1 January, 2025; originally announced January 2025.

Wannier states and spin supersolid physics in the triangular antiferromagnet K$_2$Co(SeO$_3$)$_2$

Authors: M. Zhu, Leandro M. Chinellato, V. Romerio, N. Murai, S. Ohira-Kawamura, Christian Balz, Z. Yan, S. Gvasaliya, Yasuyuki Kato, C. D. Batista, A. Zheludev

Abstract: We combine ultra-high-resolution inelastic neutron scattering and quantum Monte Carlo simulations to study thermodynamics and spin excitations in the spin-supersolid phase of the triangular lattice XXZ antiferromagnet K$_2$Co(SeO$_3$)$_2$ under zero and non-zero magnetic field. BKT transitions signaling the onset of Ising and supersolid order are clearly identified, and the Wannier entropy is expe… ▽ More We combine ultra-high-resolution inelastic neutron scattering and quantum Monte Carlo simulations to study thermodynamics and spin excitations in the spin-supersolid phase of the triangular lattice XXZ antiferromagnet K$_2$Co(SeO$_3$)$_2$ under zero and non-zero magnetic field. BKT transitions signaling the onset of Ising and supersolid order are clearly identified, and the Wannier entropy is experimentally recovered just above the supersolid phase. At low temperatures, with an experimental resolution of about 23 $μ$eV, no discrete coherent magnon modes are resolved within a broad scattering continuum. Alongside gapless excitations, a pseudo-Goldstone mode with a 0.06 meV gap is observed. A second, higher-energy continuum replaces single-spin-flip excitations of the Ising model. Under applied fields, the continuum evolves into coherent spin waves, with Goldstone and pseudo-Goldstone sectors responding differently. The experiments and simulations show excellent quantitative agreement. △ Less

Submitted 7 July, 2025; v1 submitted 27 December, 2024; originally announced December 2024.

Comments: 18 + 6 pages, 18 + 5 figures

Journal ref: npj Quantum Mater. 10, 74 (2025)

Half-Metallicity in Triangulene-based Superatomic Graphene

Authors: Yukang Ding, Tingfeng Zhang, Xiuqin Lu, Yunlong Xia, Zengfu Ou, Ye Chen, Wenya Zhai, Donghui Guo, Fengkun Chen, Meifang Zhu, Zhengfei Wang, Jingcheng Li

Abstract: The discovery of two-dimensional (2D) magnets has opened up new possibilities for miniaturizing spintronic devices to the monolayer limit. 2D half-metals, capable of conducting fully spin-polarized currents when spin-orbit coupling is minimal, provide a key advantage in improving device performance. Extensive theoretical research has been carried out to discover 2D half-metals, yet their realizati… ▽ More The discovery of two-dimensional (2D) magnets has opened up new possibilities for miniaturizing spintronic devices to the monolayer limit. 2D half-metals, capable of conducting fully spin-polarized currents when spin-orbit coupling is minimal, provide a key advantage in improving device performance. Extensive theoretical research has been carried out to discover 2D half-metals, yet their realization remains elusive. Here we report the bottom-up synthesis of superatomic graphene and the demonstration of its half-metallic properties. The produced graphene half-metal is fabricated through an on-surface synthetic approach with phosphorus-doped triangulene as its building block. Scanning tunneling microscopy measurements reveal its metallic band structures and identify its ferromagnetism through magnon excitation under varying magnetic fields. Density functional theory simulations accurately capture its half-metallic characteristics, uncovering the origin of spin-polarized bands from the p$_x,_y$-like orbital of superatomic graphene. Our work demonstrates intrinsic 2D carbon magnetism, paving the way for harnessing its advantages in spintronics. △ Less

Submitted 6 November, 2024; v1 submitted 1 November, 2024; originally announced November 2024.

Comments: Further evidence are needed for the claim of the paper

Sensitivity of Multislice Electron Ptychography to Point Defects: A Case Study in SiC

Authors: Aaditya Bhat, Colin Gilgenbach, Junghwa Kim, Michael Xu, Menglin Zhu, James M. LeBeau

Abstract: Here, we evaluate multislice electron ptychography as a tool to carry out depth-resolved atomic resolution characterization of point defects, using silicon carbide as a case study. Through multislice electron scattering simulations and multislice ptychographic reconstructions, we investigate the phase contrast arising from individual silicon vacancies, antisite defects, and a wide range of substit… ▽ More Here, we evaluate multislice electron ptychography as a tool to carry out depth-resolved atomic resolution characterization of point defects, using silicon carbide as a case study. Through multislice electron scattering simulations and multislice ptychographic reconstructions, we investigate the phase contrast arising from individual silicon vacancies, antisite defects, and a wide range of substitutional transition metal dopants (V\textsubscript{Si} to W\textsubscript{Si}) and potential detectability. Simulating defect types, positions, and microscope conditions, we show that isolated point defects can be located within a unit cell along the sample's depth. The influence of electron energy, dose, defocus, and convergence semi-angle is also explored to determine their role in governing defect contrast. These results guide experiments aiming to analyze point defects with multislice electron ptychography. △ Less

Submitted 13 May, 2025; v1 submitted 11 September, 2024; originally announced September 2024.

Bridging experiment and theory of relaxor ferroelectrics at the atomic scale with multislice electron ptychography

Authors: Menglin Zhu, Michael Xu, Yubo Qi, Colin Gilgenbach, Jieun Kim, Jiahao Zhang, Bridget R. Denzer, Lane W. Martin, Andrew M. Rappe, James M. LeBeau

Abstract: Introducing structural and/or chemical heterogeneity into otherwise ordered crystals can dramatically alter material properties. Lead-based relaxor ferroelectrics are a prototypical example, with decades of investigation having connected chemical and structural heterogeneity to their unique properties. While theory has pointed to the formation of an ensemble of ``slush''-like polar domains, the la… ▽ More Introducing structural and/or chemical heterogeneity into otherwise ordered crystals can dramatically alter material properties. Lead-based relaxor ferroelectrics are a prototypical example, with decades of investigation having connected chemical and structural heterogeneity to their unique properties. While theory has pointed to the formation of an ensemble of ``slush''-like polar domains, the lack of direct, spatially resolved volumetric data comparable to simulations presents a significant challenge in measuring the spatial distribution and correlation of local chemistry and structure with the physics underlying relaxor behavior. Here, we address this challenge through three-dimensional volumetric characterization of the prototypical relaxor ferroelectric \ce{0.68Pb(Mg$_{1/3}$Nb$_{2/3}$)O3-0.32PbTiO$_3$} using multislice electron ptychography. Direct comparison with molecular dynamics simulations reveals the intimate relationship between the polar structure and unit-cell level charge imbalance induced by chemical disorder. Further, polar nanodomains are maintained through local correlations arising from residual short-range chemical order. Acting in concert with the chemical heterogeneities, it is also shown that compressive strain enhances out-of-plane correlations and ferroelectric-like order without affecting the in-plane relaxor-like structure. Broadly, these findings provide a pathway to enable detailed atomic scale understanding for hierarchical control of polar domains in relaxor ferroelectric materials and devices, and also present significant opportunities to tackle other heterogeneous systems using complementary theoretical and experimental studies. △ Less

Submitted 21 August, 2024; originally announced August 2024.

CMOS-Compatible Ultrathin Superconducting NbN Thin Films Deposited by Reactive Ion Sputtering on 300 mm Si Wafer

Authors: Zihao Yang, Xiucheng Wei, Pinku Roy, Di Zhang, Ping Lu, Samyak Dhole, Haiyan Wang, Nicholas Cucciniello, Nag Patibandla, Zhebo Chen, Hao Zeng, Quanxi Jia, Mingwei Zhu

Abstract: We report a milestone in achieving large-scale, ultrathin (~5 nm) superconducting NbN thin films on 300 mm Si wafers using a high-volume manufacturing (HVM) industrial physical vapor deposition (PVD) system. The NbN thin films possess remarkable structural uniformity and consistently high superconducting quality across the entire 300 mm Si wafer, by incorporating an AlN buffer layer. High-resoluti… ▽ More We report a milestone in achieving large-scale, ultrathin (~5 nm) superconducting NbN thin films on 300 mm Si wafers using a high-volume manufacturing (HVM) industrial physical vapor deposition (PVD) system. The NbN thin films possess remarkable structural uniformity and consistently high superconducting quality across the entire 300 mm Si wafer, by incorporating an AlN buffer layer. High-resolution X-ray diffraction and transmission electron microscopy analyses unveiled enhanced crystallinity of (111)-oriented δ-phase NbN with the AlN buffer layer. Notably, NbN films deposited on AlN-buffered Si substrates exhibited a significantly elevated superconducting critical temperature (~2 K higher for the 10 nm NbN) and a higher upper critical magnetic field or Hc2 (34.06 T boost in Hc2 for the 50 nm NbN) in comparison with those without AlN. These findings present a promising pathway for the integration of quantum-grade superconducting NbN films with the existing 300 mm CMOS Si platform for quantum information applications. △ Less

Submitted 10 August, 2024; originally announced August 2024.

Journal ref: Materials 2023, 16, 7468

Self-consistent expansion and field-theoretic renormalization group for a singular nonlinear diffusion equation with anomalous scaling

Authors: Minhui Zhu, Nigel Goldenfeld

Abstract: The method of self-consistent expansions is a powerful tool for handling strong coupling problems that might otherwise be beyond the reach of perturbation theory, providing surprisingly accurate approximations even at low order. First applied in its embryonic form to fully-developed turbulence, it has subsequently been successfully applied to a variety of problems that include polymer statistics,… ▽ More The method of self-consistent expansions is a powerful tool for handling strong coupling problems that might otherwise be beyond the reach of perturbation theory, providing surprisingly accurate approximations even at low order. First applied in its embryonic form to fully-developed turbulence, it has subsequently been successfully applied to a variety of problems that include polymer statistics, interface dynamics and high order perturbation theory for the anharmonic oscillator. Here we show that the self-consistent expansion can be applied to singular perturbation problems arising in the theory of partial differential equations. We demonstrate its application to Barenblatt's nonlinear diffusion equation for porous media filtration, where the long-time asymptotics exhibits anomalous dimensions that can be systematically calculated using the perturbative renormalization group. We find that even the first order self-consistent expansion improves the approximation of the anomalous dimension obtained by the first-order perturbative renormalization group, especially in the strong coupling regime. We also develop a field-theoretic framework for deterministic partial differential equations to facilitate the application of self-consistent expansions to other dynamic systems, and illustrate its application using the example of Barenblatt's equation. The scope of our results on the combination of renormalization group and self-consistent expansions is limited to partial differential equations whose long-time asymptotics is controlled by incomplete similarity. However, our work suggests that these methods could be applied to a broader suite of singular perturbation problems such as boundary layer theory, multiple scales analysis and matched asymptotic expansions, for which excellent approximations using renormalization group methods alone are already available. △ Less

Submitted 13 January, 2025; v1 submitted 26 June, 2024; originally announced June 2024.

Comments: 14 pages, 1 figure

Observation of floating surface state in obstructed atomic insulator candidate NiP$_2$

Authors: Xiang-Rui Liu, Ming-Yuan Zhu, Yuanwen Feng, Meng Zeng, Xiao-Ming Ma, Yu-Jie Hao, Yue Dai, Rong-Hao Luo, Kohei Yamagami, Yi Liu, Shengtao Cui, Zhe Sun, Jia-Yu Liu, Zhengtai Liu, Mao Ye, Dawei Shen, Bing Li, Chang Liu

Abstract: Obstructed atomic insulator is recently proposed as an unconventional material, in which electric charge centers localized at sites away from the atoms. A half-filling surface state would emerge at specific interfaces cutting through these charge centers and avoid intersecting any atoms. In this article, we utilized angle-resolved photoemission spectroscopy and density functional theory calculatio… ▽ More Obstructed atomic insulator is recently proposed as an unconventional material, in which electric charge centers localized at sites away from the atoms. A half-filling surface state would emerge at specific interfaces cutting through these charge centers and avoid intersecting any atoms. In this article, we utilized angle-resolved photoemission spectroscopy and density functional theory calculations to study one of the obstructed atomic insulator candidates, NiP$_2$. A floating surface state with large effective mass that is isolated from all bulk states is resolved on the (100) cleavage plane, distinct from previously reported surface states in obstructed atomic insulators that are merged into bulk bands. Density functional theory calculation results elucidate that this floating surface state is originated from the obstructed Wannier charge centers, albeit underwent surface reconstruction that splits the half-filled obstructed surface state. Our findings not only shed lights on the spectroscopy study of obstructed atomic insulators and obstructed surface states, but also provide possible route for development of new catalysts. △ Less

Submitted 16 June, 2024; v1 submitted 8 June, 2024; originally announced June 2024.

Comments: 21 pages, 5 figures

Journal ref: npj Quantum Materials 9, 85 (2024)

Crystal facet orientation and temperature dependence of charge and spin Hall effects in noncollinear antiferromagnet: A first-principles investigation

Authors: Meng Zhu, Xinlu Li, Fanxing Zheng, Jianting Dong, Ye Zhou, Kun Wu, Jia Zhang

Abstract: Noncollinear antiferromagnets (nc-AFMs) have attracted increasing research attention in spintronics due to their unique spin structures and fascinating charge and spin transport properties. By using first-principles calculations, we comprehensively investigate the charge and spin Hall effects in representative noncollinear antiferromagnet Mn3Pt. Our study reveals that the Hall effects in nc-AFMs a… ▽ More Noncollinear antiferromagnets (nc-AFMs) have attracted increasing research attention in spintronics due to their unique spin structures and fascinating charge and spin transport properties. By using first-principles calculations, we comprehensively investigate the charge and spin Hall effects in representative noncollinear antiferromagnet Mn3Pt. Our study reveals that the Hall effects in nc-AFMs are critically dependent on the crystal facet orientation and temperature. For (001) orientated Mn3Pt, each charge and spin Hall conductivity element is comprised of both time reversal odd (T-odd) and even (T-even) contribution, associated with longitudinal conductivity, which leads to sizable and highly anisotropic Hall conductivity. The temperature dependence of charge and spin Hall conductivity has been elucidated by considering both phonon and spin disorder scattering. The scaling relations between Hall conductivity and longitudinal conductivity have also been investigated. The existence of prominent spin Hall effect in nc-AFMs may generate spin current with Sz spin polarization, which is advantageous for field free switching of perpendicular magnetization. Our work may provide unambiguous understanding on the charge and spin transport in noncollinear antiferromagnets and pave their way for applications in antiferromagnetic spintronics. △ Less

Submitted 26 May, 2024; originally announced May 2024.

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

Authors: Menglin Zhu, Joseph Lanier, Sevim Polat Genlik, Jose G. Flores, Victor da Cruz Pinha Barbosa, Mohit Randeria, Patrick M. Woodward, Maryam Ghazisaeidi, Fengyuan Yang, Jinwoo Hwang

Abstract: 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 i… ▽ More 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. △ Less

Submitted 21 May, 2024; originally announced May 2024.

Observation of Spin Splitting in Room-Temperature Metallic Antiferromagnet CrSb

Authors: Meng Zeng, Ming-Yuan Zhu, Yu-Peng Zhu, Xiang-Rui Liu, Xiao-Ming Ma, Yu-Jie Hao, Pengfei Liu, Gexing Qu, Yichen Yang, Zhicheng Jiang, Kohei Yamagami, Masashi Arita, Xiaoqian Zhang, Tian-Hao Shao, Yue Dai, Kenya Shimada, Zhengtai Liu, Mao Ye, Yaobo Huang, Qihang Liu, Chang Liu

Abstract: Recently, unconventional antiferromagnets that enable the splitting of electronic spins have been theoretically proposed and experimentally realized, where the magnetic sublattices containing moments pointing at different directions are connected by a novel set of symmetries. Such spin splitting (SS) is substantial, $k$-dependent, and independent of the spin-orbit coupling strength, making these m… ▽ More Recently, unconventional antiferromagnets that enable the splitting of electronic spins have been theoretically proposed and experimentally realized, where the magnetic sublattices containing moments pointing at different directions are connected by a novel set of symmetries. Such spin splitting (SS) is substantial, $k$-dependent, and independent of the spin-orbit coupling strength, making these magnets promising materials for antiferromagnetic spintronics. Here, combined with angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations, we perform a systematic study on CrSb, a metallic spin-split antiferromagnet candidate with $T_N$ = 703 K. Our data reveals the electronic structure of CrSb along both out-of-plane and in-plane momentum directions, which renders anisotropic $k$-dependent SS and agrees well with the calculational results. The magnitude of such SS reaches up to at least 0.8 eV at non-high-symmetry momentum points, which is significantly higher than the largest known SOC-induced SS. This compound expands the choice of materials in the field of antiferromagnetic spintronics and is likely to stimulate subsequent investigations of high-efficiency spintronic devices that are functional at room temperature. △ Less

Submitted 21 May, 2024; originally announced May 2024.

Comments: 14 pages, 4 figures

Journal ref: Advanced Science 2024, 2406529

Unconventional Unidirectional Magnetoresistance in vdW Heterostructures

Authors: I-Hsuan Kao, Junyu Tang, Gabriel Calderon Ortiz, Menglin Zhu, Sean Yuan, Rahul Rao, Jiahan Li, James H. Edgar, Jiaqiang Yan, David G. Mandrus, Kenji Watanabe, Takashi Taniguchi, Jinwoo Hwang, Ran Cheng, Jyoti Katoch, Simranjeet Singh

Abstract: Electrical readout of magnetic states is a key to realize novel spintronics devices for efficient computing and data storage. Unidirectional magnetoresistance (UMR) in bilayer systems, consisting of a spin source material and a magnetic layer, refers to a change in the longitudinal resistance upon the reversal of magnetization, which typically originates from the interaction of spin-current and ma… ▽ More Electrical readout of magnetic states is a key to realize novel spintronics devices for efficient computing and data storage. Unidirectional magnetoresistance (UMR) in bilayer systems, consisting of a spin source material and a magnetic layer, refers to a change in the longitudinal resistance upon the reversal of magnetization, which typically originates from the interaction of spin-current and magnetization at the interface. Because of UMR s linear dependence on applied charge current and magnetization, it can be used to electrically read the magnetization state. However, in conventional spin source materials, the spin polarization of an electric field induced spin current is restricted to be in the film plane and hence the ensuing UMR can only respond to the in plane component of the magnetization. On the other hand, magnets with perpendicular magnetic anisotropy (PMA) are highly desired for magnetic memory and spin-logic devices, while the electrical read out of PMA magnets through UMR is critically missing. Here, we report the discovery of an unconventional UMR in bilayer heterostructures of a topological semimetal (WTe2) and a PMA ferromagnetic insulator (Cr2Ge2Te6, CGT), which allows to electrically read the up and down magnetic states of the CGT layer by measuring the longitudinal resistance. Our theoretical calculations based on a tight binding model show that the unconventional UMR originates from the interplay of crystal symmetry breaking in WTe2 and magnetic exchange interaction across the WTe2 and CGT interface. Combining with the ability of WTe2 to obtain magnetic field free switching of the PMA magnets, our discoveries open an exciting pathway to achieve two terminal magnetic memory devices that operate solely on the spin orbit torque and UMR, which is critical for developing next-generation non volatile and low power consumption data storage technologies. △ Less

Submitted 17 May, 2024; originally announced May 2024.

Trapped-Ion Quantum Simulation of Electron Transfer Models with Tunable Dissipation

Authors: Visal So, Midhuna Duraisamy Suganthi, Abhishek Menon, Mingjian Zhu, Roman Zhuravel, Han Pu, Peter G. Wolynes, José N. Onuchic, Guido Pagano

Abstract: Electron transfer is at the heart of many fundamental physical, chemical, and biochemical processes essential for life. The exact simulation of these reactions is often hindered by the large number of degrees of freedom and by the essential role of quantum effects. Here, we experimentally simulate a paradigmatic model of molecular electron transfer using a multispecies trapped-ion crystal, where t… ▽ More Electron transfer is at the heart of many fundamental physical, chemical, and biochemical processes essential for life. The exact simulation of these reactions is often hindered by the large number of degrees of freedom and by the essential role of quantum effects. Here, we experimentally simulate a paradigmatic model of molecular electron transfer using a multispecies trapped-ion crystal, where the donor-acceptor gap, the electronic and vibronic couplings, and the bath relaxation dynamics can all be controlled independently. By manipulating both the ground-state and optical qubits, we observe the real-time dynamics of the spin excitation, measuring the transfer rate in several regimes of adiabaticity and relaxation dynamics. Our results provide a testing ground for increasingly rich models of molecular excitation transfer processes that are relevant for molecular electronics and light-harvesting systems. △ Less

Submitted 3 January, 2025; v1 submitted 16 May, 2024; originally announced May 2024.

Journal ref: Science Advances 10, eads8011 (2024)

Insights into Chemical and Structural Order at Planar Defects in a Functional Oxide Using Multislice Electron Ptychography

Authors: Menglin Zhu, Michael Xu, Yu Yun, Liyan Wu, Or Shafir, Colin Gilgenbach, Lane W. Martin, Ilya Grinberg, Jonathan E. Spanier, James M. LeBeau

Abstract: Switchable order parameters in ferroic materials are essential for functional electronic devices, yet disruptions of the ordering can take the form of planar boundaries or defects that exhibit distinct properties. Characterizing the structure of these boundaries is challenging due to their confined size and three-dimensional nature. Here, a chemical anti-phase boundary in the highly ordered double… ▽ More Switchable order parameters in ferroic materials are essential for functional electronic devices, yet disruptions of the ordering can take the form of planar boundaries or defects that exhibit distinct properties. Characterizing the structure of these boundaries is challenging due to their confined size and three-dimensional nature. Here, a chemical anti-phase boundary in the highly ordered double perovskite \ce{Pb2MgWO6} is investigated using multislice electron ptychography. The boundary is revealed to be inclined along the electron beam direction with a finite width of chemical intermixing. Additionally, regions at and near the boundary exhibit antiferroelectric-like displacements, contrasting with the predominantly paraelectric matrix. Spatial statistics and density functional theory calculations further indicate that despite their higher energy, chemical anti-phase boundaries form due to kinetic constraints during growth, with extended antiferroelectric-like distortions induced by the chemically frustrated environment in the proximity of the boundary. The three-dimensional imaging provides critical insights into the interplay between local chemistry and the polar environment, elucidating the role of anti-phase boundaries and their associated confined structural distortions and offering new opportunities for engineering ferroic thin films. △ Less

Submitted 3 October, 2024; v1 submitted 7 March, 2024; originally announced March 2024.

Shear-enhanced Liquid Crystal Spinning of Conjugated Polymer Fibers

Authors: Hao Jiang, Chi-yuan Yang, Deyu Tu, Zhu Chen, Wei Huang, Liang-wen Feng, Hengda Sun, Hongzhi Wang, Simone Fabiano, Meifang Zhu, Gang Wang

Abstract: Conjugated polymer fibers can be used to manufacture various soft fibrous optoelectronic devices, significantly advancing wearable devices and smart textiles. Recently, conjugated polymer-based fibrous electronic devices have been widely used in energy conversion, electrochemical sensing, and human-machine interaction. However, the insufficient mechanical properties of conjugated polymer fibers, t… ▽ More Conjugated polymer fibers can be used to manufacture various soft fibrous optoelectronic devices, significantly advancing wearable devices and smart textiles. Recently, conjugated polymer-based fibrous electronic devices have been widely used in energy conversion, electrochemical sensing, and human-machine interaction. However, the insufficient mechanical properties of conjugated polymer fibers, the difficulty in solution processing semiconductors with rigid main chains, and the challenges in large-scale continuous production have limited their further development in the wearable field. We regulated the pi - pi stacking interactions in conjugated polymer molecules below their critical liquid crystal concentration by applying fluid shear stress. We implemented secondary orientation, leading to the continuous fabrication of anisotropic semiconductor fibers. This strategy enables conjugated polymers with rigid backbones to synergistically enhance the mechanical and semiconductor properties of fibers through liquid crystal spinning. Furthermore, conjugated polymer fibers, exhibiting excellent electrochemical performance and high mechanical strength (600 MPa) that essentially meet the requirements for industrialized preparation, maintain stability under extreme temperatures, radiation, and chemical reagents. Lastly, we have demonstrated logic circuits using semiconductor fiber organic electrochemical transistors, showcasing its application potential in the field of wearable fabric-style logic processing. These findings confirm the importance of the liquid crystalline state and solution control in optimizing the performance of conjugated polymer fibers, thus paving the way for developing a new generation of soft fiber semiconductor devices. △ Less

Submitted 6 March, 2024; v1 submitted 5 March, 2024; originally announced March 2024.

Continuum excitations in a spin-supersolid on a triangular lattice

Authors: M. Zhu, V. Romerio, N. Steiger, S. D. Nabi, N. Murai, S. Ohira-Kawamura, K. Yu. Povarov, Y. Skourski, R. Sibille, L. Keller, Z. Yan, S. Gvasaliya, A. Zheludev

Abstract: Magnetic, thermodynamic, neutron diffraction and inelastic neutron scattering are used to study spin correlations in the easy-axis XXZ triangular lattice magnet K2Co(SeO3)2. Despite the presence of quasi-2D "supersolid" magnetic order, the low-energy excitation spectrum contains no sharp modes and is instead a broad and structured multi-particle continuum. Applying a weak magnetic field drives the… ▽ More Magnetic, thermodynamic, neutron diffraction and inelastic neutron scattering are used to study spin correlations in the easy-axis XXZ triangular lattice magnet K2Co(SeO3)2. Despite the presence of quasi-2D "supersolid" magnetic order, the low-energy excitation spectrum contains no sharp modes and is instead a broad and structured multi-particle continuum. Applying a weak magnetic field drives the system into an m = 1/3 fractional magnetization plateau phase and restores sharp spin wave modes. To some extent, the behavior at zero field can be understood in terms of spin wave decay. However, the presence of clear excitation minima at the M-points of the Brillouin zone suggest that the spinon language may provide a more adequate description, and signals a possible proximity to a Dirac spin liquid state. △ Less

Submitted 20 August, 2024; v1 submitted 29 January, 2024; originally announced January 2024.

Journal ref: Phys. Rev. Lett. 133, 186704 (2024)

Hydrogen-induced tunable remanent polarization in a perovskite nickelate

Authors: Yifan Yuan, Michele Kotiuga, Tae Joon Park, Yuanyuan Ni, Arnob Saha, Hua Zhou, Jerzy T. Sadowski, Abdullah Al-Mahboob, Haoming Yu, Kai Du, Minning Zhu, Sunbin Deng, Ravindra S. Bisht, Xiao Lyu, Chung-Tse Michael Wu, Peide D. Ye, Abhronil Sengupta, Sang-Wook Cheong, Xiaoshan Xu, Karin M. Rabe, Shriram Ramanathan

Abstract: Materials with field-tunable polarization are of broad interest to condensed matter sciences and solid-state device technologies. Here, using hydrogen (H) donor doping, we modify the room temperature metallic phase of a perovskite nickelate NdNiO3 into an insulating phase with both metastable dipolar polarization and space-charge polarization. We then demonstrate transient negative differential ca… ▽ More Materials with field-tunable polarization are of broad interest to condensed matter sciences and solid-state device technologies. Here, using hydrogen (H) donor doping, we modify the room temperature metallic phase of a perovskite nickelate NdNiO3 into an insulating phase with both metastable dipolar polarization and space-charge polarization. We then demonstrate transient negative differential capacitance in thin film capacitors. The space-charge polarization caused by long-range movement and trapping of protons dominates when the electric field exceeds the threshold value. First-principles calculations suggest the polarization originates from the polar structure created by H doping. We find that polarization decays within ~1 second which is an interesting temporal regime for neuromorphic computing hardware design, and we implement the transient characteristics in a neural network to demonstrate unsupervised learning. These discoveries open new avenues for designing novel ferroelectric materials and electrets using light-ion doping. △ Less

Submitted 20 November, 2023; originally announced November 2023.

Comments: 13 pages, 5 figures

Temporal credit assignment for one-shot learning utilizing a phase transition material

Authors: Alessandro R. Galloni, Yifan Yuan, Minning Zhu, Haoming Yu, Ravindra S. Bisht, Chung-Tse Michael Wu, Christine Grienberger, Shriram Ramanathan, Aaron D. Milstein

Abstract: Design of hardware based on biological principles of neuronal computation and plasticity in the brain is a leading approach to realizing energy- and sample-efficient artificial intelligence and learning machines. An important factor in selection of the hardware building blocks is the identification of candidate materials with physical properties suitable to emulate the large dynamic ranges and var… ▽ More Design of hardware based on biological principles of neuronal computation and plasticity in the brain is a leading approach to realizing energy- and sample-efficient artificial intelligence and learning machines. An important factor in selection of the hardware building blocks is the identification of candidate materials with physical properties suitable to emulate the large dynamic ranges and varied timescales of neuronal signaling. Previous work has shown that the all-or-none spiking behavior of neurons can be mimicked by threshold switches utilizing phase transitions. Here we demonstrate that devices based on a prototypical metal-insulator-transition material, vanadium dioxide (VO2), can be dynamically controlled to access a continuum of intermediate resistance states. Furthermore, the timescale of their intrinsic relaxation can be configured to match a range of biologically-relevant timescales from milliseconds to seconds. We exploit these device properties to emulate three aspects of neuronal analog computation: fast (~1 ms) spiking in a neuronal soma compartment, slow (~100 ms) spiking in a dendritic compartment, and ultraslow (~1 s) biochemical signaling involved in temporal credit assignment for a recently discovered biological mechanism of one-shot learning. Simulations show that an artificial neural network using properties of VO2 devices to control an agent navigating a spatial environment can learn an efficient path to a reward in up to 4 fold fewer trials than standard methods. The phase relaxations described in our study may be engineered in a variety of materials, and can be controlled by thermal, electrical, or optical stimuli, suggesting further opportunities to emulate biological learning. △ Less

Submitted 29 September, 2023; originally announced October 2023.

Comments: 37 pages, 5 figures, 6 supplementary figures

Anatomy of spin Hall effect in ferromagnetic metals

Authors: Fanxing Zheng, Jianting Dong, Xinlu Li, Meng Zhu, Ye Zhou, Jia Zhang

Abstract: The spin Hall effect in nonmagnetic materials has been intensively studied and became one of the most crucial spin-charge conversion mechanism in spintronics. However, the spin Hall effect in ferromagnetic metals has been less investigated and remains unclear. In this work, we investigate the spin Hall effect in representative ferromagnetic alloy by using first-principles calculations. We first cl… ▽ More The spin Hall effect in nonmagnetic materials has been intensively studied and became one of the most crucial spin-charge conversion mechanism in spintronics. However, the spin Hall effect in ferromagnetic metals has been less investigated and remains unclear. In this work, we investigate the spin Hall effect in representative ferromagnetic alloy by using first-principles calculations. We first clarify the spin Hall effect into three different types including conventional (CSHE), spin anomalous (SAHE) and magnetic spin Hall effect (MSHE) and then calculate the corresponding spin Hall conductivity and spin Hall angle for (Fe, Co, Ni)Pt, NiFe and CoFe alloy. We find the above three spin Hall mechanisms do coexist in ferromagnetic metals. Particularly, for Pt-based ferromagnetic alloy, a sizable conventional and magnetic spin Hall angles comparable to that of Pt have been predicted. The remarkable unconventional spin Hall effect in ferromagnetic metal may enrich the spin-charge conversion phenomena. For instance, the spin current generated by remarkable MSHE with out-of-plane spin-polarization should be helpful for field-free switching of perpendicular magnetization through spin-orbit torque effect. This work may stimulate future studies on the spin Hall effect in ferromagnetic metals and pave their promising applications for spin-charge conversion devices in spintronics. △ Less

Submitted 6 August, 2023; originally announced August 2023.

Microelectronic Morphogenesis: Progress towards Artificial Organisms

Authors: John S. McCaskill, Daniil Karnaushenko, Minshen Zhu, Oliver G. Schmidt

Abstract: Microelectronic morphogenesis is the creation and maintenance of complex functional structures by microelectronic information within shape-changing materials. Only recently has in-built information technology begun to be used to reshape materials and their functions in three dimensions to form smart microdevices and microrobots. Electronic information that controls morphology is inheritable like i… ▽ More Microelectronic morphogenesis is the creation and maintenance of complex functional structures by microelectronic information within shape-changing materials. Only recently has in-built information technology begun to be used to reshape materials and their functions in three dimensions to form smart microdevices and microrobots. Electronic information that controls morphology is inheritable like its biological counterpart, genetic information, and is set to open new vistas of technology leading to artificial organisms when coupled with modular design and self-assembly that can make reversible microscopic electrical connections. Three core capabilities of cells in organisms, self-maintenance (homeostatic metabolism utilizing free energy), self-containment (distinguishing self from non-self), and self-reproduction (cell division with inherited properties), once well out of reach for technology, are now within the grasp of information-directed materials. Construction-aware electronics can be used to proof-read and initiate game-changing error correction in microelectronic self-assembly. Furthermore, non-contact communication and electronically supported learning enable one to implement guided self-assembly and enhance functionality. This article reviews the fundamental breakthroughs that have opened the pathway to this prospective path, analyzes the extent and way in which the core properties of life can be addressed and discusses the potential and indeed necessity of such technology for sustainable high technology in society. △ Less

Submitted 3 July, 2023; v1 submitted 29 June, 2023; originally announced June 2023.

Comments: Perspective and review on an emerging field. 29 pages, 7 figures, 163 references, 3 supplementary movies available. Journal submission in progress

ACM Class: I.2.9; J.3; J.7; B.1.0; B.7.1

Journal ref: Adv. Mater. 2023, 35, 2306344

Interplay between atomic fluctuations and charge density waves in La$_{2-x}$Sr$_{x}$CuO$_{4}$

Authors: L. Shen, V. Esposito, N. G. Burdet, M. Zhu, A. N. Petsch, T. P. Croft, S. P. Collins, Z. Ren, F. Westermeier, M. Sprung, S. M. Hayden, J. J. Turner, E. Blackburn

Abstract: In the cuprate superconductors, the spatial coherence of the charge density wave (CDW) state grows rapidly below a characteristic temperature $T_\mathrm{CDW}$, the nature of which is debated. We have combined a set of x-ray scattering techniques to study La$_{1.88}$Sr$_{0.12}$CuO$_{4}$ ($T_\mathrm{CDW}$~$\approx$~80\,K) to shed light on this discussion. We observe the emergence of a crystal struct… ▽ More In the cuprate superconductors, the spatial coherence of the charge density wave (CDW) state grows rapidly below a characteristic temperature $T_\mathrm{CDW}$, the nature of which is debated. We have combined a set of x-ray scattering techniques to study La$_{1.88}$Sr$_{0.12}$CuO$_{4}$ ($T_\mathrm{CDW}$~$\approx$~80\,K) to shed light on this discussion. We observe the emergence of a crystal structure, which is consistent with the CDW modulation in symmetry, well above $T_\mathrm{CDW}$. This global structural change also induces strong fluctuations of local atomic disorder in the intermediate temperature region. At $T_\mathrm{CDW}$, the temperature dependence of this structure develops a kink, while the atomic disorder is minimized. We find that the atomic relaxation dynamics cross over from a cooperative to an incoherent response at $T_\mathrm{CDW}$. These results reveal a rich interplay between the CDWs and atomic fluctuations of distinct spatio-temporal scales. For example, the CDW coherence is enhanced on quasi-elastic timescales by incoherent atomic relaxation. △ Less

Submitted 24 April, 2023; originally announced April 2023.

Observation of plaid-like spin splitting in a noncoplanar antiferromagnet

Authors: Yu-Peng Zhu, Xiaobing Chen, Xiang-Rui Liu, Yuntian Liu, Pengfei Liu, Heming Zha, Gexing Qu, Caiyun Hong, Jiayu Li, Zhicheng Jiang, Xiao-Ming Ma, Yu-Jie Hao, Ming-Yuan Zhu, Wenjing Liu, Meng Zeng, Sreehari Jayaram, Malik Lenger, Jianyang Ding, Shu Mo, Kiyohisa Tanaka, Masashi Arita, Zhengtai Liu, Mao Ye, Dawei Shen, Jörg Wrachtrup , et al. (5 additional authors not shown)

Abstract: Spatial, momentum and energy separation of electronic spins in condensed matter systems guides the development of novel devices where spin-polarized current is generated and manipulated. Recent attention on a set of previously overlooked symmetry operations in magnetic materials leads to the emergence of a new type of spin splitting, enabling giant and momentum-dependent spin polarization of energ… ▽ More Spatial, momentum and energy separation of electronic spins in condensed matter systems guides the development of novel devices where spin-polarized current is generated and manipulated. Recent attention on a set of previously overlooked symmetry operations in magnetic materials leads to the emergence of a new type of spin splitting, enabling giant and momentum-dependent spin polarization of energy bands on selected antiferromagnets. Despite the ever-growing theoretical predictions, the direct spectroscopic proof of such spin splitting is still lacking. Here, we provide solid spectroscopic and computational evidence for the existence of such materials. In the noncoplanar antiferromagnet MnTe$_2$, the in-plane components of spin are found to be antisymmetric about the high-symmetry planes of the Brillouin zone, comprising a plaid-like spin texture in the antiferromagnetic (AFM) ground state. Such an unconventional spin pattern, further found to diminish at the high-temperature paramagnetic state, stems from the intrinsic AFM order instead of spin-orbit coupling (SOC). Our finding demonstrates a new type of quadratic spin texture induced by time-reversal breaking, placing AFM spintronics on a firm basis and paving the way for studying exotic quantum phenomena in related materials. △ Less

Submitted 4 January, 2024; v1 submitted 8 March, 2023; originally announced March 2023.

Comments: Version 3, 49 pages, 4 main figures, 13 extended data figures and 2 extended data tables. Nature in press (2024)

Journal ref: Nature 626, 523-528 (2024)

Tremendous tunneling magnetoresistance effects based on van der Waals room-temperature ferromagnet Fe$_3$GaTe$_2$ with highly spin-polarized Fermi surfaces

Authors: Xinlu Li, Meng Zhu, Yaoyuan Wang, Fanxing Zheng, Jianting Dong, Ye Zhou, Long You, Jia Zhang

Abstract: Recently, van der Waals (vdW) magnetic heterostructures have received increasing research attention in spintronics. However, the lack of room-temperature magnetic order of vdW material has largely impedes its development in practical spintronics devices. Inspired by the recently discovered vdW ferromagnet Fe3GaTe2, which has been shown to have magnetic order above room temperature and sizable perp… ▽ More Recently, van der Waals (vdW) magnetic heterostructures have received increasing research attention in spintronics. However, the lack of room-temperature magnetic order of vdW material has largely impedes its development in practical spintronics devices. Inspired by the recently discovered vdW ferromagnet Fe3GaTe2, which has been shown to have magnetic order above room temperature and sizable perpendicular magnetic anisotropy, we investigate the basic electronic structure and magnetic properties of Fe3GaTe2 as well as tunneling magnetoresistance effect in magnetic tunnel junctions (MTJs) with structure of Fe3GaTe2/Insulator/Fe3GaTe2 by using first-principles calculations. It is found that Fe3GaTe2 with highly spin-polarized Fermi surface ensures that such magnetic tunnel junctions may have prominent tunneling magnetoresistance effect at room temperature even comparable to existing conventional AlOx and MgO-based MTJs. Our results suggest that Fe3GaTe2-based MTJs may be the promising candidate for realizing long-waiting full magnetic vdW spintronic devices. △ Less

Submitted 17 November, 2022; originally announced November 2022.

Single crystal synthesis and low-lying electronic structure of V$_3$S$_4$

Authors: Yu-Jie Hao, Ming-Yuan Zhu, Xiao-Ming Ma, Chengcheng Zhang, Hongtao Rong, Qi Jiang, Yichen Yang, Zhicheng Jiang, Xiang-Rui Liu, Yupeng Zhu, Meng Zeng, Ruie Lu, Tianhao Shao, Xin Liu, Hu Xu, Zhengtai Liu, Mao Ye, Dawei Shen, Chaoyu Chen, Chang Liu

Abstract: We report successful growth of millimeter-sized high quality single crystals of V$_3$S$_4$, a candidate topological semimetal belonging to a low-symmetry space group and consisting of only low atomic number elements. Using density functional theory calculations and angle-resolved photoemission spectroscopy, we show that the nonmagnetic phase of monoclinic V$_3$S$_4$ hosts type-II Dirac-like quasip… ▽ More We report successful growth of millimeter-sized high quality single crystals of V$_3$S$_4$, a candidate topological semimetal belonging to a low-symmetry space group and consisting of only low atomic number elements. Using density functional theory calculations and angle-resolved photoemission spectroscopy, we show that the nonmagnetic phase of monoclinic V$_3$S$_4$ hosts type-II Dirac-like quasiparticles which opens a sizable gap due to spin orbit coupling, as well as theoretical multiple nodal lines that are eliminated also by spin orbit coupling. These results suggest that relativistic effects give rise to profound modifications of the topological properties even in compounds with low-weight elements. △ Less

Submitted 25 March, 2023; v1 submitted 9 August, 2022; originally announced August 2022.

Comments: 19 Pages, 3 Figures. To be published in Journal of Alloys and Compounds

Multiplication of freestanding semiconductor membranes from a single wafer by advanced remote epitaxy

Authors: Hyunseok Kim, Yunpeng Liu, Kuangye Lu, Celesta S. Chang, Kuan Qiao, Ki Seok Kim, Bo-In Park, Junseok Jeong, Menglin Zhu, Jun Min Suh, Yongmin Baek, You Jin Ji, Sungsu Kang, Sangho Lee, Ne Myo Han, Chansoo Kim, Chanyeol Choi, Xinyuan Zhang, Haozhe Wang, Lingping Kong, Jungwon Park, Kyusang Lee, Geun Young Yeom, Sungkyu Kim, Jinwoo Hwang , et al. (4 additional authors not shown)

Abstract: Freestanding single-crystalline membranes are an important building block for functional electronics. Especially, compounds semiconductor membranes such as III-N and III-V offer great opportunities for optoelectronics, high-power electronics, and high-speed computing. Despite huge efforts to produce such membranes by detaching epitaxial layers from donor wafers, however, it is still challenging to… ▽ More Freestanding single-crystalline membranes are an important building block for functional electronics. Especially, compounds semiconductor membranes such as III-N and III-V offer great opportunities for optoelectronics, high-power electronics, and high-speed computing. Despite huge efforts to produce such membranes by detaching epitaxial layers from donor wafers, however, it is still challenging to harvest epitaxial layers using practical processes. Here, we demonstrate a method to grow and harvest multiple epitaxial membranes with extremely high throughput at the wafer scale. For this, 2D materials are directly formed on III-N and III-V substrates in epitaxy systems, which enables an advanced remote epitaxy scheme comprised of multiple alternating layers of 2D materials and epitaxial layers that can be formed by a single epitaxy run. Each epilayer in the multi-stack structure is then harvested by layer-by-layer peeling, producing multiple freestanding membranes with unprecedented throughput from a single wafer. Because 2D materials allow peeling at the interface without damaging the epilayer or the substrate, wafers can be reused for subsequent membrane production. Therefore, this work represents a meaningful step toward high-throughput and low-cost production of single-crystal membranes that can be heterointegrated. △ Less

Submitted 7 April, 2022; originally announced April 2022.

Kinetically-controlled epitaxial growth of Fe$_3$GeTe$_2$ van der Waals ferromagnetic films

Authors: Wenyi Zhou, Alexander J. Bishop, Menglin Zhu, Igor Lyalin, Robert C. Walko, Jay A. Gupta, Jinwoo Hwang, Roland K. Kawakami

Abstract: We demonstrate that kinetics play an important role in the epitaxial growth of Fe$_3$GeTe$_2$ (FGT) van der Waals (vdW) ferromagnetic films by molecular beam epitaxy. By varying the deposition rate, we control the formation or suppression of an initial tellurium-deficient non-van der Waals phase (Fe$_3$Ge$_2$) prior to realizing epitaxial growth of the vdW FGT phase. Using cross-sectional scanning… ▽ More We demonstrate that kinetics play an important role in the epitaxial growth of Fe$_3$GeTe$_2$ (FGT) van der Waals (vdW) ferromagnetic films by molecular beam epitaxy. By varying the deposition rate, we control the formation or suppression of an initial tellurium-deficient non-van der Waals phase (Fe$_3$Ge$_2$) prior to realizing epitaxial growth of the vdW FGT phase. Using cross-sectional scanning transmission electron microscopy and scanning tunneling microscopy, we optimize the FGT films to have atomically smooth surfaces and abrupt interfaces with the Ge(111) substrate. The magnetic properties of our high quality material are confirmed through magneto-optic, magnetotransport, and spin-polarized STM studies. Importantly, this demonstrates how the interplay of energetics and kinetics can help tune the re-evaporation rate of chalcogen atoms and interdiffusion from the underlayer, which paves the way for future studies of van der Waals epitaxy. △ Less

Submitted 8 February, 2022; originally announced February 2022.

Comments: 18 pages, 4 figures

Journal ref: ACS Appl. Electron. Mater. 4, 3190 (2022)

Spin fluctuations associated with the collapse of the pseudogap in a cuprate superconductor

Authors: M. Zhu, D. J. Voneshen, S. Raymond, O. J. Lipscombe, C. C. Tam, S. M. Hayden

Abstract: Theories of the origin of superconductivity in cuprates are dependent on an understanding of their normal state which exhibits various competing orders. Transport and thermodynamic measurements on La$_{2-x}$Sr$_x$CuO$_4$ show signatures of a quantum critical point, including a peak in the electronic specific heat $C$ versus doping $p$, near the doping $p^{\star}$ where the pseudogap collapses. The… ▽ More Theories of the origin of superconductivity in cuprates are dependent on an understanding of their normal state which exhibits various competing orders. Transport and thermodynamic measurements on La$_{2-x}$Sr$_x$CuO$_4$ show signatures of a quantum critical point, including a peak in the electronic specific heat $C$ versus doping $p$, near the doping $p^{\star}$ where the pseudogap collapses. The fundamental nature of the fluctuations associated with this peak is unclear. Here we use inelastic neutron scattering to show that close to $T_c$ and near $p^{\star}$, there are very-low-energy collective spin excitations with characteristic energies $\hbar Γ\approx$~5 meV. Cooling and applying a 8.8~T magnetic field creates a mixed state with a stronger magnetic response below 10~meV. We conclude that the low-energy spin-fluctuations are due to the collapse of the pseudogap combined with an underlying tendency to magnetic order. We show that the large specific heat near $p^{\star}$ can be understood in terms of collective spin fluctuations. The spin fluctuations we measure exist across the superconducting phase diagram and may be related to the strange metal behaviour observed in overdoped cuprates. △ Less

Submitted 22 August, 2023; v1 submitted 27 January, 2022; originally announced January 2022.

Comments: Final author version

Journal ref: Nature Physics 19, 99 (2023)

Tunneling Magnetoresistance in Noncollinear Antiferromagnetic Tunnel Junctions

Authors: Jianting Dong, Xinlu Li, Gautam Gurung, Meng Zhu, Peina Zhang, Fanxing Zheng, Evgeny Y. Tsymbal, Jia Zhang

Abstract: Antiferromagnetic (AFM) spintronics has emerged as a subfield of spintronics driven by the advantages of antiferromagnets producing no stray fields and exhibiting ultrafast magnetization dynamics. The efficient method to detect an AFM order parameter, known as the Néel vector, by electric means is critical to realize concepts of AFM spintronics. Here, we demonstrate that non-collinear AFM metals,… ▽ More Antiferromagnetic (AFM) spintronics has emerged as a subfield of spintronics driven by the advantages of antiferromagnets producing no stray fields and exhibiting ultrafast magnetization dynamics. The efficient method to detect an AFM order parameter, known as the Néel vector, by electric means is critical to realize concepts of AFM spintronics. Here, we demonstrate that non-collinear AFM metals, such as Mn3Sn, exhibit a momentum dependent spin polarization which can be exploited in AFM tunnel junctions to detect the Néel vector. Using first-principles calculations based on density functional theory, we predict a tunneling magnetoresistance (TMR) effect as high as 300% in AFM tunnel junctions with Mn3Sn electrodes, where the junction resistance depends on the relative orientation of their Néel vectors and exhibits four non-volatile resistance states. We argue that the spin-split band structure and the related TMR effect can also be realized in other non-collinear AFM metals like Mn3Ge, Mn3Ga, Mn3Pt, and Mn3GaN. Our work provides a robust method for detecting the Néel vector in non-collinear antiferromagnets via the TMR effect, which may be useful for their application in AFM spintronic devices. △ Less

Submitted 27 March, 2022; v1 submitted 13 December, 2021; originally announced December 2021.

Radiation-hardened and Repairable MoS$_2$ Field Effect Devices with Polymer Solid Electrolyte Gates

Authors: Di Chen, Jiankun Li, Zheng Wei, Xinjian Wei, Maguang Zhu, Jing Liu, Guangyu Zhang, Zhiyong Zhang, Jian-Hao Chen

Abstract: As human activities expand into naturally or man-made radiation-prone environment, the need for radiation-hardened (Rad-Hard) electronic hardware surged. The state-of-the-art silicon-based and two-dimensional (2D) materials based Rad-Hard transistors can withstand up to 1 Mrad (Si) of total ionization dose (TID), while higher TID tolerance is being heatedly sought after. Here we present few-layer… ▽ More As human activities expand into naturally or man-made radiation-prone environment, the need for radiation-hardened (Rad-Hard) electronic hardware surged. The state-of-the-art silicon-based and two-dimensional (2D) materials based Rad-Hard transistors can withstand up to 1 Mrad (Si) of total ionization dose (TID), while higher TID tolerance is being heatedly sought after. Here we present few-layer MoS$_2$ Rad-Hard field-effect transistors (FETs) with polymer solid electrolyte (PSE) gate dielectrics. The MoS$_2$ PSE-FETs exhibit a TID tolerance of up to 3.75 Mrad (Si) at a dose rate of 523 rad (Si) s$^{-1}$ and can be repaired with a moderate thermal annealing at 100 $^{\circ}$C for 5 minutes. Combining the excellent intrinsic radiation tolerance and the reparability, the MoS$_2$ PSE-FETs reach a TID tolerance of up to 10 Mrad (Si). Complementary metal-oxide-semiconductor (CMOS)-like MoS$_2$ PSE-inverters have been built and show similar high radiation tolerance. Furthermore, the feasibility of wafer-scale Rad-Hard PSE-inverter array has been demonstrated using chemical vapor deposition (CVD) grown monolayer MoS$_2$. Our studies uncover the potential of 2D materials based PSE devices in future Rad-Hard integrated circuits (ICs). △ Less

Submitted 6 October, 2021; originally announced October 2021.

Comments: 20 pages, 12 figures

Journal ref: Adv. Electron. Mater. 2021,2100619

Current-Perpendicular-to-Plane Giant Magnetoresistance Effect in van der Waals Heterostructures

Authors: Xinlu Li, Yurong Su, Meng Zhu, Fanxing Zheng, Peina Zhang, Jia Zhang, Jing-Tao Lü

Abstract: Spin-dependent transport in a full van der Waals (vdW) giant magnetoresistance (GMR) junctions with the structure of Fe3GeTe2/XTe2/Fe3GeTe2 (X = Pt, Pd) has been investigated by using first-principles calculations. The ballistic conductance, magnetoresistance (MR) and resistance-area product (RA) have been calculated in a current-perpendicular-to-plane (CPP) geometry. A giant magnetoresistance of… ▽ More Spin-dependent transport in a full van der Waals (vdW) giant magnetoresistance (GMR) junctions with the structure of Fe3GeTe2/XTe2/Fe3GeTe2 (X = Pt, Pd) has been investigated by using first-principles calculations. The ballistic conductance, magnetoresistance (MR) and resistance-area product (RA) have been calculated in a current-perpendicular-to-plane (CPP) geometry. A giant magnetoresistance of around 2000% and RA less than 0.3 Ω μm2 have been found in the proposed vdW CPP GMR. In addition, the spin-orbit coupling effect on transport and anisotropy magnetoresistance (AMR) has also been investigated. The calculated AMR is found to be around 20% in Fe3GeTe2/trilayer-PdTe2/Fe3GeTe2 CPP GMR. Both GMR and AMR in the proposed vdW CPP GMR mainly originate from the bulk electronic structure properties of Fe3GeTe2. This work demonstrates a vdW CPP GMR with superior advantages including perpendicular magnetic anisotropy, large GMR, low RA as well as sizable AMR may stimulate future experimental explorations and should be appealing for their applications in spintronic devices including magnetic sensor and memory. △ Less

Submitted 6 October, 2021; originally announced October 2021.

Journal ref: Phys Rev Applied (2021)

Ferroelectric control of Néel vector in L10 type of antiferromagnetic films

Authors: Fanxing Zheng, Meng Zhu, Xinlu Li, Peina Zhang, Jiuzhao Liu, Jianting Dong, Jia Zhang

Abstract: How to efficiently manipulate the Néel vector of antiferromagnets (AFM) by electric methods is one of the major focuses in current antiferromagnetic spintronics. In this work, we investigated the ferroelectric control of magnetism in AFM L10-MnPt/BaTiO3 bilayers structures by using first-principles calculation. We studied the effect of ferroelectric polarization reversal on magnetic crystalline an… ▽ More How to efficiently manipulate the Néel vector of antiferromagnets (AFM) by electric methods is one of the major focuses in current antiferromagnetic spintronics. In this work, we investigated the ferroelectric control of magnetism in AFM L10-MnPt/BaTiO3 bilayers structures by using first-principles calculation. We studied the effect of ferroelectric polarization reversal on magnetic crystalline anisotropy (MCA) of L10-MnPt films with different interface structures. Our results predict a large perpendicular MCA in L10-MnPt films with Pt-O interface, while an in-plane MCA with Mn-O interface when they are interfaced with ferroelectric BaTiO3. In addition, the magnitude of MCA for both interfaces can be modulated efficiently by the polarization reversal of BaTiO3. The ferroelectric control of MCA has been analyzed based on second order perturbation theory, and it can be mainly attributed to the ferroelectric polarization driven redistribution of Pt-5d orbital occupation around Fermi energy. Especially, for Mn-O interface, the Néel vector can be switched between in-plane [100] and [110] directions, or even from in-plane to out-of-plane at certain film thickness by reversing ferroelectric polarization. Our results may provide a non-volatile concept for ferroelectric control of Néel vector in L10-antiferromagnets, which could stimulate experimental investigations on magnetoelectric effect of antiferromagnets and promote its applications in low-power consumption spintronic memory devices. △ Less

Submitted 6 October, 2021; originally announced October 2021.

Journal ref: Phys Rev B (2021)