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Spontaneous oscillations and geometric cutoff in confined bacterial swarms
Authors:
Bing Miao,
Lei-Han Tang
Abstract:
Self-organized dynamic patterns in dense active matter are striking manifestations of non-equilibrium physics. A prominent example is the macroscopic elliptical motion observed in quasi-2D bacterial suspensions, which has lacked a physical explanation. Here, we examine a minimal linear response framework coupling bacterial swimming dynamics with fluid flow, treating long-range hydrodynamic interac…
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Self-organized dynamic patterns in dense active matter are striking manifestations of non-equilibrium physics. A prominent example is the macroscopic elliptical motion observed in quasi-2D bacterial suspensions, which has lacked a physical explanation. Here, we examine a minimal linear response framework coupling bacterial swimming dynamics with fluid flow, treating long-range hydrodynamic interactions as a macroscopic communication channel. We demonstrate that microscopic swim motion, via Jeffery coupling, manifests as a ``phase-leading'' response to local shear flows. System-wide sustained oscillations, on the other hand, require both a critical bacterial density and strict geometric confinement. By analytically predicting the onset cell density and maximum film thickness, our model achieves excellent quantitative agreement with experiments, establishing a unified physical framework for self-organized periodic motion of elongated body in active fluids.
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Submitted 2 June, 2026; v1 submitted 26 March, 2026;
originally announced March 2026.
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Path-integrals and optimal paths for the fractional Ornstein-Uhlenbeck process
Authors:
Bing Miao,
Gleb Oshanin,
Luca Peliti
Abstract:
We derive the path-integral representation of the fractional Ornstein-Uhlenbeck process driven by Riemann-Liouville fractional Gaussian noise, for both the subdiffusive and superdiffusive regimes. We express the corresponding action, which is a quadratic functional of individual trajectories of the process, in two alternative but equivalent forms: either as a fractional integral or as a double int…
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We derive the path-integral representation of the fractional Ornstein-Uhlenbeck process driven by Riemann-Liouville fractional Gaussian noise, for both the subdiffusive and superdiffusive regimes. We express the corresponding action, which is a quadratic functional of individual trajectories of the process, in two alternative but equivalent forms: either as a fractional integral or as a double integral with a nonlocal kernel. Moreover, we determine in closed form the optimal (action-minimizing) paths conditioned to reach a prescribed point at a fixed time moment and discuss their behavior, which appears to be non-intuitive for subdiffusive processes in the presence of a strong confining potential.
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Submitted 1 December, 2025;
originally announced December 2025.
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Neo-Gibbsian Statistical Energetics with Applications to Nonequilibrium Cells
Authors:
Bing Miao,
Hong Qian,
Yong-Shi Wu
Abstract:
Generalization through novel interpretations of the inner logic of the century-old Gibbs' statistical thermodynamics is presented: i) Identifying $k_B\to 0$ as classical energetics, one directly derives a pair of thermodynamic variational formulae \[
F(T) = \min_{E\ge E_{min}}\Big\{E-TS(E) \Big\}
\,\text{ and }\
S(E) = \min_{T>0}\left\{\frac{E}{T}-\frac{F(T)}{T} \right\}, \] that dictate all…
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Generalization through novel interpretations of the inner logic of the century-old Gibbs' statistical thermodynamics is presented: i) Identifying $k_B\to 0$ as classical energetics, one directly derives a pair of thermodynamic variational formulae \[
F(T) = \min_{E\ge E_{min}}\Big\{E-TS(E) \Big\}
\,\text{ and }\
S(E) = \min_{T>0}\left\{\frac{E}{T}-\frac{F(T)}{T} \right\}, \] that dictate all the more familiar $1/T=d S(E)/d E$, $E=d\{F(T)/T\}/d(1/T)$, and $S(E)=-d F(T)/d T$ in equilibrium, which is maintained by a duality symmetry with one-to-one relation between $T^{\text{eq}}(E)=\arg\min_T\{E/T-F(T)/T\}$ and $E^{\text{eq}}(T)=\arg\min_E\{E-TS(E)\}$. ii) In contradistinction, taking derivative of the statistical free energy w.r.t. $T$, a mesoscopic energetics with fluctuations emerges: This yields two information entropy functions which historically appeared 50 years postdate Gibbs' theory. iii) Combining the above pair of inequalities yields an irreversible thermodynamic potential $ψ(T,E) \equiv \{E-F(T)\}/T-S(E)\ge 0$ for nonequilibrium states. The second law of thermodynamics as a universal principle reflects $ψ\ge 0$ due to a disagreement between $E$ and $T$ as a dual pair. Our theory provides a new energetics of living cells which are nonequilibrium, complex entities under constant $T$, pressure $p$ and chemical potential $μ$. $ψ$ provides a ``distance'' between statistical data from a large ensemble of cells and a set of intrinsic energetic parameters that encode the information within.
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Submitted 24 August, 2025;
originally announced August 2025.
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Solving Lyapunov equations for electrically driven ternary electrolytes -- application to long-range van der Waals interactions
Authors:
Guangle Du,
Bing Miao,
David S. Dean
Abstract:
Stochastic density functional theory (SDFT) has been widely used to study the out of equilibrium properties of electrolyte solutions. Examples include investigations of electrical conductivity -- both within and beyond linear response -- and modifications of thermal van der Waals interactions in driven electrolytes. Within the approximation scheme derived from linearizing SDFT for fluctuations aro…
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Stochastic density functional theory (SDFT) has been widely used to study the out of equilibrium properties of electrolyte solutions. Examples include investigations of electrical conductivity -- both within and beyond linear response -- and modifications of thermal van der Waals interactions in driven electrolytes. Within the approximation scheme derived from linearizing SDFT for fluctuations around mean densities, the steady state correlation functions between the $N$ ionic species are governed by linear Lyapunov equations of degree $N(N+1)/2$. Consequently, the system's complexity increases significantly when transitioning from binary to ternary electrolytes, and few analytical results exist for the latter. In this paper, we demonstrate how -- for the specific case of electrolytes -- the Lyapunov equations can be reduced to a system of $N$ linear equations. We apply this reduction to compute the long-range component of the van der Waals interaction between two slabs containing a ternary electrolyte under an applied electric field parallel to the slabs. Unlike the binary electrolyte case, we show that the resulting van der Waals interaction for a ternary electrolyte depends on the ionic species' diffusion coefficients, highlighting its inherently out of equilibrium nature.
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Submitted 19 May, 2025;
originally announced May 2025.
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Entropy Production in Non-Gaussian Active Matter: A Unified Fluctuation Theorem and Deep Learning Framework
Authors:
Yuanfei Huang,
Chengyu Liu,
Bing Miao,
Xiang Zhou
Abstract:
We present a general framework for deriving entropy production rates (EPRs) in active matter systems driven by non-Gaussian active fluctuations. Employing the probability-flow equivalence technique, we rigorously obtain an entropy production (EP) decomposition formula. We demonstrate that the EP, $Δs_\mathrm{tot}$, satisfies a detailed fluctuation theorem,…
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We present a general framework for deriving entropy production rates (EPRs) in active matter systems driven by non-Gaussian active fluctuations. Employing the probability-flow equivalence technique, we rigorously obtain an entropy production (EP) decomposition formula. We demonstrate that the EP, $Δs_\mathrm{tot}$, satisfies a detailed fluctuation theorem, $ρ_{\mathcal{R}}(Σ)/ρ_{\mathcal{R}}(-Σ)=e^Σ$, which holds for the distribution $ρ_{\mathcal{R}}(Σ)$ defined as the probability of observing a value $Σ$ of the quantity $\mathcal{R}\equiv Δs_\mathrm{tot}-B_\mathrm{act}$, where $B_\mathrm{act}$ is a path-dependent random variable associated with active fluctuations. Moreover, an integral fluctuation theorem, $\langle e^{- \mathcal{R} } \rangle = 1$, and the generalized second law of thermodynamics, $\langle Δs_\mathrm{tot} \rangle \ge \langle B_\mathrm{act} \rangle$, follow directly. Our results hold under steady-state conditions and can be straightforwardly extended to arbitrary initial states. In the limiting case where active fluctuations vanish, these theorems reduce to the established results of stochastic thermodynamics. Building on this theoretical foundation, we introduce a deep-learning-based methodology for efficiently computing the EP, utilizing the Lévy score we propose. To illustrate the validity of our approach, we apply it to two representative systems: a Brownian particle in a periodic active bath and an active polymer composed of an active Brownian cross-linker interacting with passive Brownian beads. Our work provides a unified framework for analyzing EP in active matter and offers practical computational tools for investigating complex nonequilibrium behavior.
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Submitted 10 December, 2025; v1 submitted 9 April, 2025;
originally announced April 2025.
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Repulsive thermal van der Waals interaction in multi-species asymmetric electrolytes driven by external electric fields
Authors:
Guangle Du,
David S. Dean,
Bing Miao,
Rudolf Podgornik
Abstract:
It is well established that the long-range component of the thermal van der Waals interaction between two semi-infinite dielectrics becomes short-range when an electrolyte is present between them, this is the well known phenomenon of screening. In Phys. Rev. Lett, 133, 238002 (2024) it was shown that for a binary symmetric electrolyte, an electric field parallel to the dielectric boundaries disrup…
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It is well established that the long-range component of the thermal van der Waals interaction between two semi-infinite dielectrics becomes short-range when an electrolyte is present between them, this is the well known phenomenon of screening. In Phys. Rev. Lett, 133, 238002 (2024) it was shown that for a binary symmetric electrolyte, an electric field parallel to the dielectric boundaries disrupts screening and a long-range thermal repulsive interaction appears. At large applied fields this long-range repulsive interaction can be explained by the fact that the cations and anions have differing average drifts moving in opposite directions, leading to the correlation of charge density fluctuations between the two species to decouple. Here we extend these results to binary electrolytes which are asymmetric as well as electrolytes with more than two ionic species.
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Submitted 20 January, 2025;
originally announced January 2025.
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Emergence of Newtonian Deterministic Causality from Stochastic Motions in Continuous Space and Time
Authors:
Bing Miao,
Hong Qian,
Yong-Shi Wu
Abstract:
Since Newton's time, deterministic causality has been considered a crucial prerequisite in any fundamental theory in physics. In contrast, the present work investigates stochastic dynamical models for motion in one spatial dimension, in which Newtonian mechanics becomes an emergent property: We present a coherent theory in which a Hamilton-Jacobi equation (HJE) emerges in a description of the evol…
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Since Newton's time, deterministic causality has been considered a crucial prerequisite in any fundamental theory in physics. In contrast, the present work investigates stochastic dynamical models for motion in one spatial dimension, in which Newtonian mechanics becomes an emergent property: We present a coherent theory in which a Hamilton-Jacobi equation (HJE) emerges in a description of the evolution of entropy $-φ(x,t)=ε\log$(Probability) of a system under observation and in the limit of large information extent $ε^{-1}$ in homogeneous space and time. The variable $φ$ represents a non-random high-order statistical concept that is distinct from probability itself as $ε=0$; the HJE embodies an emergent law of deterministic causality in continuous space and time with an Imaginary Scale symmetry $(t,x,φ)\leftrightarrow (it,ix,-iφ)$. $φ(x,t)$ exhibits a nonlinear wave phenomenon with a mathematical singularity in finite time, overcoming which we introduce viscosity $ε(\partial^2φ/\partial x^2)$ and wave $iε(\partial^2 φ/\partial x^2)$ perturbations, articulating dissipation and conservation, which break the Imaginary Scale symmetry: They lead to the Brownian motion and Schrödinger's equation of motion, respectively. Last but not least, Lagrange's action in classical mechanics acquires an entropic interpretation and Hamilton's principle is established.
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Submitted 2 February, 2025; v1 submitted 4 June, 2024;
originally announced June 2024.
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Correlation decoupling of Casimir interaction in an electrolyte driven by external electric fields
Authors:
Guangle Du,
David S. Dean,
Bing Miao,
Rudolf Podgornik
Abstract:
It has been established for a long time that the long range van der Waals or thermal Casimir interaction between two semi-infinite dielectrics separated by a distance $H$ is screened by an intervening electrolyte. Here we show how this interaction is modified when an electric field of strength $E$ is applied parallel to the dielectric boundaries, leading to a non-equilibrium steady state with a cu…
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It has been established for a long time that the long range van der Waals or thermal Casimir interaction between two semi-infinite dielectrics separated by a distance $H$ is screened by an intervening electrolyte. Here we show how this interaction is modified when an electric field of strength $E$ is applied parallel to the dielectric boundaries, leading to a non-equilibrium steady state with a current. The presence of the field induces a long range thermal repulsive interaction, scaling just like the thermal Casimir interaction between dielectrics without the intervening electrolyte, {\em i.e.} as $1/H^3$. At small $E$ the effect is of order $E^2$ while at large fields it saturates to an $E$ independent value. We explain the results in terms of a decoupling mechanism between the charge density fluctuations of cations and anions at large applied fields.
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Submitted 21 January, 2025; v1 submitted 9 April, 2024;
originally announced April 2024.
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On Thermodynamic Information
Authors:
Bing Miao,
Hong Qian,
Yong-Shi Wu
Abstract:
Information based thermodynamic logic is revisited. It consists of two parts: Part A applies the modern theory of probability in which an arbitrary convex function φis employed as an analytic "device" to express information as statistical dependency contained in the topological sub-σ-algebra structure. Via thermo-doubling, Fenchel-Young equality (FYE) that consists of φ(x) and its conjugate ψ(y) e…
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Information based thermodynamic logic is revisited. It consists of two parts: Part A applies the modern theory of probability in which an arbitrary convex function φis employed as an analytic "device" to express information as statistical dependency contained in the topological sub-σ-algebra structure. Via thermo-doubling, Fenchel-Young equality (FYE) that consists of φ(x) and its conjugate ψ(y) establishes the notion of equilibrium between x and y through duality symmetry and the principle of maximum entropy/minimum free energy. Part B deals with a given set of repetitive measurements, where an inherent convex function emerges via the mathematics of large deviations. Logarithm-based Shannon entropy with φ(x)=-\log x figures prominently for i.i.d. sample statistics. Information can be a measure of the agreement between a statistical observation and its theoretical models. Maximum likelihood principle arises here and FYE provides a thermodynamic energetic narrative of recurrent data.
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Submitted 6 December, 2023;
originally announced December 2023.
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Anomalous Nernst effect induced terahertz emission in a single ferromagnetic film
Authors:
Zheng Feng,
Wei Tan,
Zuanming Jin,
Yi-Jia Chen,
Zhangfeng Zhong,
Liang Zhang,
Song Sun,
Jin Tang,
Yexing Jiang,
Po-Hsun Wu,
Jun Cheng,
Bingfeng Miao,
Haifeng Ding,
Dacheng Wang,
Yiming Zhu,
Liang Guo,
Sunmi Shin,
Guohong Ma,
Dazhi Hou,
Ssu-Yen Huang
Abstract:
By developing a bidirectional-pump terahertz (THz) emission spectroscopy, we reveal an anomalous Nernst effect (ANE) induced THz emission in a single ferromagnetic film. Based on the distinctive symmetry of the THz signals, ANE is unequivocally distinguished from the previously attributed ultrafast demagnetization and anomalous Hall effect mechanisms. A quantitative method is established to separa…
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By developing a bidirectional-pump terahertz (THz) emission spectroscopy, we reveal an anomalous Nernst effect (ANE) induced THz emission in a single ferromagnetic film. Based on the distinctive symmetry of the THz signals, ANE is unequivocally distinguished from the previously attributed ultrafast demagnetization and anomalous Hall effect mechanisms. A quantitative method is established to separate the different contributions, demonstrating a significant ANE contribution that even overwhelms other competing mechanisms. Our work not only clarifies the origin of the ferromagnetic-based THz emission, but also offers a fertile platform for investigating the ultrafast magnetism and THz spintronics.
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Submitted 16 June, 2023; v1 submitted 21 February, 2023;
originally announced February 2023.
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Topological linear magnetoresistivity and thermoconductivity induced by noncentrosymmetric Berry curvature
Authors:
Min-Xue Yang,
Hai-Dong Li,
Wei Luo,
Bingfeng Miao,
Wei Chen,
D. Y. Xing
Abstract:
The Berry curvature plays a key role in the magnetic transport of topological materials. Yet, it is not clear whether the Berry curvature by itself can give rise to universal transport phenomena with specific scaling behaviors. In this work, based on the semiclassical Boltzmann formalism and the symmetry analysis, we show that the noncentrosymmetric distribution of the Berry curvature generally re…
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The Berry curvature plays a key role in the magnetic transport of topological materials. Yet, it is not clear whether the Berry curvature by itself can give rise to universal transport phenomena with specific scaling behaviors. In this work, based on the semiclassical Boltzmann formalism and the symmetry analysis, we show that the noncentrosymmetric distribution of the Berry curvature generally results in linear magnetoresistivity and thermoconductivity both exhibiting the B-scaling behavior. We then study such kind of topological linear magnetoresistivity in the 2D MnBi2Te4 flakes and the 3D spin-orbit-coupled electron gas, the former showing good agreement with the experimental observations. The difference between our mechanism and the conventional anisotropic magnetoresistance is elucidated. Our theory proposes a universal scenario for the topological linear magnetoresistivity and thermoconductivity and predicts such effects to occur in various materials, which also provides a reasonable explanation for the recent observations of linear magnetoresistivity.
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Submitted 18 April, 2023; v1 submitted 15 December, 2022;
originally announced December 2022.
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Lieb lattices formed by real atoms on Ag(111) and their lattice constant dependent electronic properties
Authors:
Xiaoxia Li,
Qili Li,
Tongzhou Ji,
Ruige Yan,
Wenlin Fan,
Bingfeng Miao,
Liang Sun,
Gong Chen,
Weiyi Zhang,
Haifeng Ding
Abstract:
Scanning tunneling microscopy is a powerful tool to build artificial atomic structures even not exist in nature but possess exotic properties. We here constructed Lieb lattices with different lattice constants by real atoms, i.e., Fe atoms on Ag(111) and probed their electronic properties. We find a surprising long-range effective electron wavefunction overlap between Fe adatoms as it exhibits a 1…
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Scanning tunneling microscopy is a powerful tool to build artificial atomic structures even not exist in nature but possess exotic properties. We here constructed Lieb lattices with different lattice constants by real atoms, i.e., Fe atoms on Ag(111) and probed their electronic properties. We find a surprising long-range effective electron wavefunction overlap between Fe adatoms as it exhibits a 1/r2-dependence with the interatomic distance r instead of the theoretically predicted exponential one. Combining control experiments, tight-binding and Green's function calculations, we attribute the observed long-range overlap to be enabled by the surface state. Our findings not only enrich the understanding of the electron wavefunction overlap, but also provide a convenient platform to design and explore the artificial structures and future devices with real atoms.
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Submitted 2 May, 2022;
originally announced May 2022.
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Planar Hall effect induced spin rectification effect and its strong impact on spin pumping measurements
Authors:
Kang He,
Jun Cheng,
Man Yang,
Yihui Zhang,
Longqian Yu,
Qi Liu,
Liang Sun,
Bingfeng Miao,
Canming Hu,
Haifeng Ding
Abstract:
Spin pumping is a technique widely used to generate the pure spin current and characterize the spin-charge conversion in various systems. The reversing sign of the symmetric Lorentzian charge current with respect to opposite magnetic field is generally accepted as the key criterion to identify its pure spin current origin. However, we herein find that the rectified voltage due to the planar Hall e…
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Spin pumping is a technique widely used to generate the pure spin current and characterize the spin-charge conversion in various systems. The reversing sign of the symmetric Lorentzian charge current with respect to opposite magnetic field is generally accepted as the key criterion to identify its pure spin current origin. However, we herein find that the rectified voltage due to the planar Hall effect can exhibit similar spurious signal, complicating and even misleading the analysis. The distribution of microwave magnetic field and induction current has strong influence on the magnetic field symmetry and lineshape of the obtained signal. We further demonstrate a geometry where the spin-charge conversion and the rectified voltage can be readily distinguished with a straightforward symmetry analysis.
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Submitted 5 January, 2022; v1 submitted 19 November, 2021;
originally announced November 2021.
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Thermal Casimir interactions for higher derivative field Lagrangians: generalized Brazovskii models
Authors:
David S. Dean,
Bing Miao,
Rudolf Podgornik
Abstract:
We examine the Casimir effect for free statistical field theories which have Hamiltonians with second order derivative terms. Examples of such Hamiltonians arise from models of non-local electrostatics, membranes with non-zero bending rigidities and field theories of the Brazovskii type that arise for polymer systems. The presence of a second derivative term means that new types of boundary condit…
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We examine the Casimir effect for free statistical field theories which have Hamiltonians with second order derivative terms. Examples of such Hamiltonians arise from models of non-local electrostatics, membranes with non-zero bending rigidities and field theories of the Brazovskii type that arise for polymer systems. The presence of a second derivative term means that new types of boundary conditions can be imposed, leading to a richer phenomenology of interaction phenomena. In addition zero modes can be generated that are not present in standard first derivative models, and it is these zero modes which give rise to long range Casimir forces. Two physically distinct cases are considered: (i) unconfined fields, usually considered for finite size embedded inclusions in an infinite fluctuating medium, here in a two plate geometry the fluctuating field exists both inside and outside the plates, (ii) confined fields, where the field is absent outside the slab confined between the two plates. We show how these two physically distinct cases are mathematically related and discuss a wide range of commonly applied boundary conditions. We concentrate our analysis to the critical region where the underlying bulk Hamiltonian has zero modes and show that very exotic Casimir forces can arise, characterised by very long range effects and oscillatory behavior that can lead to strong metastability in the system.
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Submitted 22 February, 2020;
originally announced February 2020.
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Path integrals for higher derivative actions
Authors:
David S. Dean,
Bing Miao,
Rudi Podgornik
Abstract:
We consider Euclidean path integrals with higher derivative actions, including those that depend quadratically on acceleration, velocity and position. Such path integrals arise naturally in the study of stiff polymers, membranes with bending rigidity as well as a number of models for electrolytes. The approach used is based on the relation between quadratic path integrals and Gaussian fields and w…
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We consider Euclidean path integrals with higher derivative actions, including those that depend quadratically on acceleration, velocity and position. Such path integrals arise naturally in the study of stiff polymers, membranes with bending rigidity as well as a number of models for electrolytes. The approach used is based on the relation between quadratic path integrals and Gaussian fields and we also show how it can be extended to the evaluation of even higher order path integrals.
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Submitted 1 November, 2019; v1 submitted 20 June, 2019;
originally announced June 2019.
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Anatomy of electrical signals and dc-voltage lineshape in spin torque ferromagnetic resonance
Authors:
Yin Zhang,
Q. Liu,
B. F. Miao,
H. F. Ding,
X. R. Wang
Abstract:
The electrical detection of spin torque ferromagnetic resonance (st-FMR) is becoming a popular method for measuring the spin-Hall angle of heavy metals (HM). However, various sensible analysis on the same material with either the same or different experimental setups yielded different spin-Hall angles with large discrepancy, indicating some missing ingredients in our current understanding of st-FM…
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The electrical detection of spin torque ferromagnetic resonance (st-FMR) is becoming a popular method for measuring the spin-Hall angle of heavy metals (HM). However, various sensible analysis on the same material with either the same or different experimental setups yielded different spin-Hall angles with large discrepancy, indicating some missing ingredients in our current understanding of st-FMR. Here we carry out a careful analysis of electrical signals of the st-FMR in a HM/ferromagnet (HM/FM) bilayer with an arbitrary magnetic anisotropy. The FM magnetization is driven by two radio-frequency (rf) forces: the rf Oersted field generated by an applied rf electric current and the so called rf spin-orbit torque from the spin current flowing perpendicularly from the HM to the FM due to the spin-Hall effect. By using the universal form of the dynamic susceptibility matrix of magnetic materials at the st-FMR, the electrical signals originated from the anisotropic magnetoresistance, anomalous Hall effect and inverse spin-Hall effect are analysed and dc-voltage lineshape near the st-FMR are obtained. Angle-dependence of dc-voltage is given for two setups. A way of experimentally extracting the spin-Hall angle of a HM is proposed.
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Submitted 2 November, 2018;
originally announced November 2018.
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Highly-efficient spintronic terahertz emitter enabled by metal-dielectric photonic crystal
Authors:
Zheng Feng,
Rui Yu,
Yu Zhou,
Hai Lu,
Wei Tan,
Hu Deng,
Quancheng Liu,
Zhaohui Zhai,
Liguo Zhu,
Jianwang Cai,
Bingfeng Miao,
Haifeng Ding
Abstract:
Spintronic terahertz (THz) emitter provides the advantages such as apparently broader spectrum, significantly lower cost, and more flexibility in compared with the commercial THz emitters, and thus attracts great interests recently. In past few years, efforts have been made in optimizing the material composition and structure geometry, and the conversion efficiency has been improved close to that…
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Spintronic terahertz (THz) emitter provides the advantages such as apparently broader spectrum, significantly lower cost, and more flexibility in compared with the commercial THz emitters, and thus attracts great interests recently. In past few years, efforts have been made in optimizing the material composition and structure geometry, and the conversion efficiency has been improved close to that of ZnTe crystal. One of the drawbacks of the current designs is the rather limited laser absorption - more than 50% energy is wasted and the conversion efficiency is thus limited. Here, we theoretically propose and experimentally demonstrate a novel device that fully utilizes the laser intensity and significantly improves the conversion efficiency. The device, which consists of a metal-dielectric photonic crystal structure, utilizes the interference between the multiple scattering waves to simultaneously suppress the reflection and transmission of the laser, and to reshape the laser field distributions. The experimentally detected laser absorption and THz generations show one-to-one correspondence with the theoretical calculations. We achieve the strongest THz pulse emission that presents a 1.7 times improvement compared to the currently designed spintronic emitter. This work opens a new pathway to improve the performance of spintronic THz emitter from the perspective of optics.
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Submitted 9 July, 2018;
originally announced July 2018.
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Electrical Detection of Direct and Alternating Spin Current Injected from a Ferromagnetic Insulator into a Ferromagnetic Metal
Authors:
P. Hyde,
Lihui Bai,
D. M. J. Kumar,
B. W. Southern,
S. Y. Huang,
B. F. Miao,
C. L. Chien,
C. -M. Hu
Abstract:
We report room temperature electrical detection of spin injection from a ferromagnetic insulator (YIG) into a ferromagnetic metal (Permalloy, Py). Non-equilibrium spins with both static and precessional spin polarizations are dynamically generated by the ferromagnetic resonance of YIG magnetization, and electrically detected by Py as dc and ac spin currents, respectively. The dc spin current is el…
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We report room temperature electrical detection of spin injection from a ferromagnetic insulator (YIG) into a ferromagnetic metal (Permalloy, Py). Non-equilibrium spins with both static and precessional spin polarizations are dynamically generated by the ferromagnetic resonance of YIG magnetization, and electrically detected by Py as dc and ac spin currents, respectively. The dc spin current is electrically detected via the inverse spin Hall effect of Py, while the ac spin current is converted to a dc voltage via the spin rectification effect of Py which is resonantly enhanced by dynamic exchange interaction between the ac spin current and the Py magnetization. Our results reveal a new path for developing insulator spintronics, which is distinct from the prevalent but controversial approach of using Pt as the spin current detector.
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Submitted 17 October, 2013;
originally announced October 2013.
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Electronically Guided Self Assembly within Quantum Corrals
Authors:
R. X. Cao,
B. F. Miao,
Z. F. Zhong,
L. Sun,
B. You,
W. Zhang,
D. Wu,
An Hu,
S. D. Bader,
H. F. Ding
Abstract:
A grand challenge of nanoscience is to master the control of structure and properties in order to go beyond present day functionality. The creation of nanostructures via atom manipulation by means of a scanning probe represents one of the great achievements of the nano era. Here we build on this achievement to self-assemble nanostructures within quantum corrals. The structuring is guided by the qu…
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A grand challenge of nanoscience is to master the control of structure and properties in order to go beyond present day functionality. The creation of nanostructures via atom manipulation by means of a scanning probe represents one of the great achievements of the nano era. Here we build on this achievement to self-assemble nanostructures within quantum corrals. The structuring is guided by the quantum confinement of the electronic density of a silver metallic substrate within the corrals. We experimentally demonstrate different self-organized Gd atomic structures confined within 30-nm circular and triangular Fe quantum corrals. This approach enables the creation of model systems to explore and understand new nanomaterials and device prototypes.
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Submitted 6 September, 2012;
originally announced September 2012.