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The preparation of two-dimensional magnetic materials is a key process to their applications and the study of their structure and morphology plays an important role in the growth of high-quality thin films. Here, the growth, structure, and morphology of Cr1+δTe2 films grown by molecular beam epitaxy on mica with variations of Te/Cr flux ratio, growth temperature, and film thickness have been systematically investigated by scanning tunneling microscopy, reflection high-energy electron diffraction, scanning electron microscope, and X-ray photoelectron spectroscopy. We find that a structural change from multiple phases to a single phase occurs with the increase in growth temperature, irrespective of the Cr/Te flux ratios, which is attributed to the desorption difference of Te atoms at different temperatures, and that the surface morphology of the films grown at relatively high growth temperatures (≥ 300 °C) exhibits a quasi-hexagonal mesh-like structure, which consists of nano-islands with bending surface induced by the screw dislocations, as well as that the films would undergo a growth-mode change from 2D at the initial stage in a small film thickness (2 nm) to 3D at the later stage in thick thicknesses (12 nm and 24 nm). This work provides a general model for the study of pseudo-layered materials grown on flexible layered substrates.

Preparation of atomic reconstructions and tracking its dynamic-evolutionary pathways for some polar surfaces of ionic crystals are essential in surface science but remain a formidable challenge. Mainly by scanning tunneling microscopy, we investigate various reconstructions as well as their dynamic-evolutionary pathways on ZnO(0001) surface as a prototypical ionic crystal, which have been successfully prepared by introducing Ga surface segregation. We observe three complex pathways from an initial disorder to finally well-ordered surface with (2×8) reconstruction undergoing complicated atom desorption, missing and moving dynamic processes, one of which is “disorder → [disorder + (√3 × √3)R30°] → [(2 × 2)] → zigzag arrangement → [(2 × 8)]”. The atomic reconstructions are proposed to originate from the modification of empty states of dangling bonds of the surface by surface segregation. Our findings provide a general model for preparing plentifully atomic reconstructions and revealing dynamic-evolutionary pathways on complex polar surfaces of ionic crystals.

Signaling proteins are composed of conserved protein interaction domains that serve as allosteric regulatory elements of enzymatic or binding activities. The ubiquitous, structurally conserved cyclic nucleotide binding (CNB) domain is found covalently linked to proteins with diverse folds that perform multiple biological functions. Given that the structures of cAMP-bound CNB domains in different proteins are very similar, it remains a challenge to determine how this domain allosterically regulates such diverse protein functions and folds. Instead of a structural perspective, we focus our attention on the energy landscapes underlying the CNB domains and their responses to cAMP binding. We show that optical tweezers is an ideal tool to investigate how cAMP binding coupled to interdomain interactions remodel the energy landscape of the regulatory subunit of protein kinase A (PKA), which harbors two CNB domains. We mechanically manipulate and probe the unfolding and refolding behavior of the CNB domains as isolated structures or selectively as part of the PKA regulatory subunit, and in the presence and absence of cAMP. Optical tweezers allows us to dissect the changes in the energy landscape associated with cAMP binding, and to examine the allosteric interdomain interactions triggered by the cyclic nucleotide. This single molecule approach can be used to study other modular, multidomain signaling proteins found in nature.

Via exploring the spin dynamics and transport properties at interfaces of magnetic material/non-magnetic metal bilayers, spintronics advanced many techniques on generation, detection, and manipulation of spin currents, which laid down a foundation for designing spintronic devices. New ideas and methods for manipulating spin are required in the spintronics community. Merging with cavity quantum electrodynamics, magnetic resonance in ferromagnets inside of a microwave cavity, realizes a strong magnon-microwave coupling at room temperature, opening an avenue to manipulate spin and spin current for the spintronics community. Spin-microwave coupling strength was significantly improved by replacing a few spins in a paramagnetic spin system with magnetization in ferromagnetic materials. Thus, a strongly coupled magnon-microwave system offers a hybrid quantum platform with many measures to tune the coupled system, such as an exchange magnetic field, an anisotropy field, controlled coupling strength, controlled damping parameters, and so on. Many devices were proposed and demonstrated with potential applications. In this review, we briefly introduce the concept and mechanism of magnon-microwave coupling, a classical electrodynamical coupling model for the coupling, spin currents produced by the coupled magnon, and manipulation of the spin current via the strong coupling. In ferromagnets, magnons can couple to a microwave mode as a magnon-polariton propagating in the materials. The strongly coupled magnon-microwave system is a magnon-polariton in a cavity where the microwave was confined as a resonance mode with a high quality factor. Using the Landau-Lifshitz-Gilbert equation and Maxwell equations, we introduce the classical electrodynamical coupling model and reveal that the magnon is driven by a torque produced by the microwave magnetic field on the magnetization and the microwave is feedback via Faraday’s law. Therefore, the coupling strength of the magnon-microwave system can be controlled by changing the torque. Magnon-microwave coupling is experimentally studied using many techniques, such as microwave transmission, Brillouin light scattering, Faraday rotation measurement, and spin pumping electrical detection. Spin pumping is well explored in the spintronics community as a spin current produced by magnon and detected as a voltage via inverse spin Hall effect in a novel metal. Combining with microwave transmission of the coupled microwave subsystem, spin pumping electrical detection by directly detecting the spin current produced by the magnon subsystem in the coupled system, illustrates a more complete profile of the coupled magnon-microwave system. In addition, the strongly coupled magnon-microwave system offers a new technique to manipulate spin currents. We experimentally demonstrate that spin currents produced by the strongly coupled system are correlated with each other mediated by the microwave cavity, and can be manipulated remotely. Two almost identical magnet samples are used to couple to a cavity and the coupling strengths between each magnet and the cavity are tunable individually. By using electrical detection to locally detect each magnet sample respectively, we find that the spin currents produced by two magnet samples are coherently correlated. By tuning the coupling strength of one magnet sample to the cavity, the spin current produced by the second magnet sample is manipulated distantly over a few centimeters, which is far longer than the distance of spin-orbit interaction or exchange interaction. This distant control is only limited by the coherence length of the microwave and the dimension of the cavity. This flexibility opens the door to improve spin current generation and manipulation for cavity spintronic devices.

Cyclic-nucleotide binding (CNB) domains are structurally and evolutionarily conserved signaling modules that regulate proteins with diverse folds and functions. Despite a wealth of structural information, the mechanisms by which CNB domains couple cyclic-nucleotide binding to conformational changes involved in signal transduction remain unknown. Here we combined single-molecule and computational approaches to investigate the conformation and folding energetics of the two CNB domains of the regulatory subunit of protein kinase A (PKA). We found that the CNB domains exhibit different conformational and folding signatures in the apo state, when bound to cAMP, or when bound to the PKA catalytic subunit, underscoring their ability to adapt to different binding partners. Moreover, we show while the two CNB domains have near-identical structures, their thermodynamic coupling signatures are divergent, leading to distinct cAMP responses and differential mutational effects. Specifically, we demonstrate mutation W260A exerts local and allosteric effects that impact multiple steps of the PKA activation cycle. Taken together, these results highlight the complex interplay between folding energetics, conformational dynamics, and thermodynamic signatures that underlies structurally conserved signaling modules in response to ligand binding and mutational effects.

Novel spintronic devices with low power consumption, nonvolatility, and high storage density are highly desired to meet the rapid development of modern information storage and communication technology, which poses a great challenge to both material and device researches. To overcome this challenge, our group has focused our research on the following two aspects. On one hand, we have explored novel magnetoresistance effects in a variety of materials and devices, aiming to get a deep understanding about the spin dependent transport and obtain an effective control of spin-dependent transport. On the other hand, we have tried to control the magnetoresistance based on multi-physical field effects, aiming to obtain spintronic prototype devices that can be used for multi-state data storage. Regarding the novel magnetoresistance explorations, this article will introduce: (1) The negative magnetoresistance in amorphous condensed magnetic semiconductors. The spin dependent variable range hopping model is proposed, which can quantitatively explain the temperature and magnetic field dependent transport behavior in the condensed magnetic semiconductors. In addition, this model provides an alternative way to detect the spin polarization ratio of the magnetic semiconductors. (2) The positive magnetoresistance in single-crystal CoZnO magnetic semiconductors. By quantitative analysis of the transport properties of CoZnO films, it is observed that the positive magnetoresistance in the “hard gap” regime is the result of the carrier wavefunction shrinkage under applied magnetic field. (3) The rectification magnetoresistance in non-magnetic Schottky heterojunctions and the tunneling rectification magnetoresistance in magnetic tunnel junctions. A brand new rectification magnetoresistance is observed in nonmagnetic Al/Ge Schottky heterojunctions: The application of a pure small sinusoidal alternating current to the nonmagnetic Schottky heterojunctions can generate a significant direct-current voltage, and this rectification voltage strongly varies with the external magnetic field. Moreover, by using CoO-ZnO composite tunneling barrier, the charge-related rectification and spin-dependent tunneling magnetoresistance are integrated into the Co/CoO-ZnO/Co magnetic tunneling junctions to realize the tunneling rectification magnetoresistance. The observation of rectification magnetoresistance and tunneling rectification magnetoresistance not only adds new members to the magnetoresistance family, but also provides a promising way to control the devices’ properties by using alternating current. In terms of multistate data storage application, this review will introduce: (1) The electrical and magnetic field controllable 4 resistance states in oxide heterojunctions. In Co/CoO-ZnO/Co magnetic tunneling junctions, by integrating the electrical field induced resistance switching and the magnetic field induced tunneling magnetoresistance effects, four nonvolatile resistance states are demonstrated. (2) The remanent magnetization controllable 10 resistance states in magnetic heterojunctions. Here, a general remanent magnetism engineering method is proposed for realizing multiple reliable magnetic and resistance states, not depending on a specific material or device structure. Especially, as a proof-of-concept demonstration, ten states of nonvolatile memory based on the manipulation of ferromagnetic remanent magnetization have been revealed in both Co/Pt magnetic multilayers with strong perpendicular magnetic anisotropy and MgO-based magnetic tunneling junctions at room temperature. (3) The spin-orbit torque controllable 10 resistance states in single-layer magnetic alloy. A repeatable bulk spin-orbit torque switching of the perpendicularly magnetized CoPt alloy single-layer films is realized by introducing a composition gradient in the thickness direction to break the inversion symmetry. Moreover, a ten states nonvolatile memory is illustrated solely by changing the electrical current to control the multi-domain states of the CoPt alloy.

Material functionalities strongly depend on the stoichiometry, crystal structure, and homogeneity. Here we demonstrate an approach of amorphous nonstoichiometric inhomogeneous oxides to realize tunable ferromagnetism and electrical transport at room temperature. In order to verify the origin of the ferromagnetism, we employed a series of structural, chemical, and electronic state characterizations. Combined with electron microscopy and transport measurements, synchrotron-based grazing incident wide angle X-ray scattering, soft X-ray absorption and circular dichroism clearly reveal that the room-temperature ferromagnetism originates from the In0.23Co0.77O1−v amorphous phase with a large tunable range of oxygen vacancies. The room-temperature ferromagnetism is tunable from a high saturation magnetization of 500 emu cm−3 to below 25 emu cm−3, with the evolving electrical resistivity from 5 × 103 μΩ cm to above 2.5 × 105 μΩ cm. Inhomogeneous nano-crystallization emerges with decreasing oxygen vacancies, driving the system towards non-ferromagnetism and insulating regime. Our work unfolds the novel functionalities of amorphous nonstoichiometric inhomogeneous oxides, which opens up new opportunities for developing spintronic materials with superior magnetic and transport properties.

How to electrically control magnetic properties of a magnetic material is promising towards spintronic applications, where the investigation of carrier doping effects on antiferromagnetic (AFM) materials remains challenging due to their zero net magnetization. In this work, we found electron doping dependent variation of magnetic orders of a two-dimensional (2D) AFM insulator NiPS3, where doping concentration is tuned by intercalating various organic cations into the van der Waals gaps of NiPS3 without introduction of defects and impurity phases. The doped NiPS3 shows an AFM-ferrimagnetic (FIM) transition at doping level of 0.2-0.5 electrons/cell and a FIM-AFM transition at doping level of >= 0.6 electrons/cell. We propose that the found phenomenon is due to competition between Stoner exchange dominated inter-chain ferromagnetic order and super-exchange dominated inter-chain AFM order at different doping level. Our studies provide a viable way to exploit correlation between electronic structures and magnetic properties of 2D magnetic materials for realization of magnetoelectric effect., 18 pages, 7 figures

We report an unconventional carrier-dependent anomalous Hall effect (AHE) with a quadratic scaling relation in epitaxial films of a ferromagnetic semiconductor (ZnCo)O with a high Co concentration. We show the co-existence of AHE together with the nonlinear ordinary Hall effect (NLHE) and the separation of NLHE by using a two-conducting channels model in the expression of Hall resistivity. We found that the NLHE depends strongly on both temperature and carrier density n and dominates at low temperature when n

Programmable magnetic field-free manipulation of perpendicular magnetization switching is essential for the development of ultralow-power spintronic devices. However, the magnetization in a centrosymmetric single-layer ferromagnetic film cannot be switched directly by passing an electrical current in itself. Here, we demonstrate a repeatable bulk spin-orbit torque (SOT) switching of the perpendicularly magnetized CoPt alloy single-layer films by introducing a composition gradient in the thickness direction to break the inversion symmetry. Experimental results reveal that the bulk SOT-induced effective field on the domain walls leads to the domain walls motion and magnetization switching. Moreover, magnetic field-free perpendicular magnetization switching caused by SOT and its switching polarity (clockwise or counterclockwise) can be reversibly controlled in the IrMn/Co/Ru/CoPt heterojunctions based on the exchange bias and interlayer exchange coupling. This unique composition gradient approach accompanied with electrically controllable SOT magnetization switching provides a promising strategy to access energy-efficient control of memory and logic devices., A major challenge of spintronics is achieving magnetic field free electrical control of magnetisation. Here, Xie et al. achieve perpendicular magnetisation switching in a CoPt alloy, breaking inversion symmetry by varying the composition of the alloy in the growth direction.

We study a partner selection problem for virtual manufacturing enterprises facing an uncertain environment. We propose a new method of using the grey system theory to account for uncertainties in a project's start time, completion time, transportation time, as well as cost. We first develop the concepts of delivery time agreement index and cost agreement index, and then formulate a multi-objective partner selection problem that maximizes the minimum delivery time agreement index, the average delivery time agreement index and the cost agreement index. A chaotic particle swarm optimization (CPSO) algorithm is developed. Extensive computational results show that the proposed CPSO method outperforms the standard PSO in providing quality solutions more reliably.

In designing spintronic devices, control of spin-current transport at the interface of a magnetic material and a normal metal is key. In general, spin current in metallic materials is limited to the nanometer scale by the spin diffusion length. Using an ionic-gating technique, this study experimentally demonstrates control of the spin current due to spin pumping in a yttrium-iron-garnet/Pt bilayer using a gate voltage. This result helps to better understand spin transfer at magnetic-insulator/heavy-metal interfaces, and therefore enables improved spintronic devices.

The Rabi oscillations of a coupled spin-photon system are experimentally studied using time domain microwave transmission measurements. An external magnetic bias field is applied to control the amplitude and frequency of Rabi oscillations, which are a measure of the coherent spin-photon energy exchange and coupling strength respectively. The amplitude and frequency control is described in the time domain as the transient response of a two-level spin-photon system. This approach reveals the link between steady state and transient behaviour of the cavity-magnon-polariton, which is necessary to interpret time domain cavity-spintronic experiments. This transient model also allows us to understand and quantify the polariton mode composition, which can be controlled by the bias field.

We consider a real-time emergency medical service (EMS) vehicle patient transportation problem in which vehicles are assigned to patients so they can be transported to hospitals during an emergency. The objective is to minimize the total travel time of all vehicles while satisfying two types of time window constraints. The first requires each EMS vehicle to arrive at a patient’s location within a specified time window. The second requires the vehicle to arrive at the designated hospital within another time window. We allow an EMS vehicle to serve up to two patients instead of just one. The problem is shown to be NP-complete. We, therefore, develop a simulated annealing (SA) heuristic for efficient solution in real-time. A column generation algorithm is developed for determining a tight lower bound. Numerical results show that the proposed SA heuristic provides high-quality solutions in much less CPU time, when compared to the general-purpose solver. Therefore, it is suitable for implementation in a real-time decision support system, which is available via a web portal ( www.rtdss.org ).

A systematic study of the electrodynamic coupling between the ferromagnetic resonance (FMR) and the cavity mode of a microwave cavity is presented. The nature of the FMR and cavity modes, described by their resonance position and line width, is measured and compared with a classical model based on the Landau–Lifshitz–Gilbert equation and an RLC circuit, which explicitly implement Faraday’s and Ampere’s laws. The relationship between the coupling gap, which can be accessed experimentally, and the coupling strength, which is a fundamental property of the FMR/cavity system, is discussed on the basis of this model. A straightforward method is experimentally developed to control the coupling gap. The capability of using such a tunable cavity-FMR coupling in combination with spin pumping could provide us with new technologies that utilize the light-matter interaction to control spin current in cavity spintronics.

Spin transfer torque (STT) driven by a charge current plays a key role in magnetization switching in heavy-metal/ferromagnetic-metal structures. The STT efficiency defined by the ratio between the effective field due to STT and the current density, is required to be improved to reduce energy compulsions in the STT-based spintronic devices. In this work, using the harmonic Hall measurement method, we experimentally studied the STT efficiency in platinum(Pt)/FM structures as a function of the Pt thickness. We found that the STT efficiency strongly depends on the Pt thickness and reaches a maximum value of 4.259 mT/($10^6$A/$cm^{2}$) for the 1.8-nm-thickness Pt sample. This result indicates that competition between spin Hall effect (SHE) and Rashba effect as well as spin diffusion process across the Pt layer determines the Pt thickness for the maximum STT efficiency. We demonstrated the role played by the spin diffusion besides the spin current generation mechanisms in improvement of the STT efficiency, which is helpful in designing STT-based devices., Comment: 6 pages 4 figures

Protein kinases are dynamic molecular switches that sample multiple conformational states. The regulatory subunit of PKA harbors two cAMP-binding domains [cyclic nucleotide-binding (CNB) domains] that oscillate between inactive and active conformations dependent on cAMP binding. The cooperative binding of cAMP to the CNB domains activates an allosteric interaction network that enables PKA to progress from the inactive to active conformation, unleashing the activity of the catalytic subunit. Despite its importance in the regulation of many biological processes, the molecular mechanism responsible for the observed cooperativity during the activation of PKA remains unclear. Here, we use optical tweezers to probe the folding cooperativity and energetics of domain communication between the cAMP-binding domains in the apo state and bound to the catalytic subunit. Our study provides direct evidence of a switch in the folding-energy landscape of the two CNB domains from energetically independent in the apo state to highly cooperative and energetically coupled in the presence of the catalytic subunit. Moreover, we show that destabilizing mutational effects in one CNB domain efficiently propagate to the other and decrease the folding cooperativity between them. Taken together, our results provide a thermodynamic foundation for the conformational plasticity that enables protein kinases to adapt and respond to signaling molecules.

Strong coupling in cavity-magnon systems has shown great potential for use in spintronics and information processing technologies due to the low damping rates and long coherence times. Although such systems are conceptually similar to those coupled by magnon-polaritons (MPs), the link between magnon-cavity coupling and MPs has not been explicitly defined. In this work we establish such a connection by studying the frequency-wavevector dispersion of a strongly coupled magnon-cavity system, using a height-adjustable microwave cavity, and by modelling the observed behaviour through the system's effective permeability. A polariton gap between the upper and lower coupled modes of the magnon-cavity system is defined, and is seen to be dependent on the system's effective filling factor. This gap is equal to the MP polariton gap in the limit where filling factor = 1, corresponding to the removal of the microwave cavity. Thus, our work clarifies the connection between magnon-cavity and MP coupling, improving our understanding of magnon-photon interactions in coupled systems.

Using electrical detection of a strongly coupled spin-photon system comprised of a microwave cavity mode and two magnetic samples, we demonstrate the long distance manipulation of spin currents. This distant control is not limited by the spin diffusion length, instead depending on the interplay between the local and global properties of the coupled system, enabling systematic spin current control over large distance scales (several centimeters in this work). This flexibility opens the door to improved spin current generation and manipulation for cavity spintronic devices., Comment: 5 pages, 3 figures

We experimentally studied a strongly coupled magnon-photon system via microwave transmission measurements. An anti-resonance, i.e. the suppression of the microwave transmission, is observed, indicating a relative phase change between the magnon response and the driving microwave field. We show that this anti-resonance feature can be used to interpret the phase evolution of the coupled magnon-microwave system and apply this technique to reveal the phase evolution of magnon dark modes. Our work provides a standard procedure for the phase analysis of strongly coupled systems, enabling the phase characterization of each subsystem, and can be generally applied to other strongly coupled systems., 6 pages, 3 figures

This work was supported by the National Science Foundation of China (Grant Nos. 11434006, 11774199, and 51871112), the National Basic Research Program of China (Grant No. 2015CB921502), the 111 ProjectB13029, and the Taishan Scholar Program of Shandong Province. H.Z. was supported by the King Abdullah University of Science and Technology (KAUST) during his visit to KAUST. X.X.Z. acknowledges the support from KAUST.

This paper addresses the toll pricing problem in which the objective is to minimize the number of required toll facilities in a traffic network. The problem is shown to be NP-hard. To obtain a solution in a reasonable time, an effective metaheuristic algorithm is developed. The algorithm uses a local search technique in which the neighborhood function employs the dynamic slope scaling procedure to deal with the fixed charge nature of the objective function. Numerical results from 50 randomly generated and three real networks are reported.

We address a toll pricing problem in which the objective is to minimize the number of required toll facilities in a transportation network while inducing drivers to make the most efficient collective use of the network. We formulate the problem as a mixed-integer programming model and propose a solution method using combinatorial Benders cuts. Computational study of real networks as well as randomly generated networks indicates that our proposed method is efficient in obtaining provably optimal solutions for networks with small to medium sizes.

We experimentally and theoretically investigate the microwave transmission line shape of the cavity-magnon-polariton (CMP) created by inserting a low damping magnetic insulator into a high quality 3D microwave cavity. While fixed field measurements are found to have the expected Lorentzian characteristic, at fixed frequencies the field swept line shape is in general asymmetric. Such fixed frequency measurements demonstrate that microwave transmission can be used to access magnetic characteristics of the CMP, such as the field line width $\Delta H$. By developing an effective oscillator model of the microwave transmission we show that these line shape features are general characteristics of harmonic coupling. At the same time, at the classical level the underlying physical mechanism of the CMP is electrodynamic phase correlation and a second model based on this principle also accurately reproduces the experimental line shape features. In order to understand the microscopic origin of the effective coupled oscillator model and to allow for future studies of CMP phenomena to extend into the quantum regime, we develop a third, microscopic description, based on a Green's function formalism. Using this method we calculate the transmission spectra and find good agreement with the experimental results., Comment: 12 pages, 6 figures

We use electrical detection, in combination with microwave transmission, to investigate both resonant and non-resonant magnon-photon coupling at room temperature. Spin pumping in a dynamically coupled magnon-photon system is found to be distinctly different from previous experiments. Characteristic coupling features such as modes anti-crossing, line width evolution, peculiar line shape, and resonance broadening are systematically measured and consistently analyzed by a theoretical model set on the foundation of classical electrodynamic coupling. Our experimental and theoretical approach pave the way for pursuing microwave coherent manipulation of pure spin current via the combination of spin pumping and magnon-photon coupling., Comment: 5 pages, 3 figures

Spin rectification in a single crystal Fe/Au/Fe sandwich is electrically detected for collinear and non-collinear magnetization and external magnetic field configurations. The line shape, line width and signal polarity are analysed. The spin rectication theory has been much extended by taking the magneto-crystalline anisotropy and shape anisotropy into account, which explained non-collinear resonances and agrees very well with experimental data. Thus, a comprehensive understanding of spin rectification in ferromagnetic metal was demonstrated in this work.

This article examines the problem of assigning individuals to teams to make the teams as similar as possible to each other across multiple attributes. This may be complicated by a variety of constraints, including restrictions on whether specific individuals can or should be assigned to the same team. The problem arises in multiple contexts, including youth recreation leagues and academic programs or courses with mandated project groups. A model for the problem is proposed and various solution approaches are investigated, including mixed-integer programming and several heuristics. Supplementary materials are available for this article. Go to the publisher’s online edition of IIE Transactions for datasets, additional tables, detailed proofs, etc.

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., 5 pages, 4 figures

We develop a method for universally resolving the important issue of separating spin pumping (SP) from spin rectification (SR) signals in bilayer spintronics devices. This method is based on the characteristic distinction of SP and SR, as revealed in their different angular and field symmetries. It applies generally for analyzing charge voltages in bilayers induced by the ferromagnetic resonance (FMR), independent of FMR line shape. Hence, it solves the outstanding problem that device specific microwave properties restrict the universal quantification of the spin Hall angle in bilayer devices via FMR experiments. Furthermore, it paves the way for directly measuring the nonlinear evolution of spin current generated by spin pumping. The spin Hall angle in a Py/Pt bilayer is thereby directly measured as 0.021$\pm$0.015 up to a large precession cone angle of about 20$^{\circ}$., 5 pages, 4 figures

We experimentally realize an indirect coupling between two cavity modes via strong coupling with ferromagnetic resonance in Yttrium Iron Garnet. We find that some indirectly coupled modes of this system can have a higher microwave transmission than the individual uncoupled modes. Using a coupled harmonic oscillator model, the influence of the oscillation phase difference between the two cavity modes on the nature of the indirect coupling is revealed. The properties of the indirectly coupled modes can be controlled using an external magnetic field or by tuning the cavity height. The relation between cavity transmission and the relative phase difference between cavity modes should be useful for developing tunable optical devices and improved information processing technologies.

Clinic of University of Louisville is a relatively new medical clinic which attempts to stem the epidemic of childhood obesity. The main problem addressed by this research is the no show rate (nearly 50%) of the clinic. There are two goals in this project. One is to increase the staff utilization; the other is to decrease the waiting time. We study two potential methods to solve this problem. One involves using multiple resources for every visit; the other involves overbooking the patients. One simulation model is an overbooking model in which the interarrival times are controlled for each type of patients. By increasing arrival rate of patients, the waiting time, the total number of served patients and the utilization of staff are increased. We need to trade off in order to choose the best arrival rate for the clinic. The second model involves using multiple resources for every visit. We also change the interarrival time for patients in order to estimate the best values for these inputs.

We report direct observation of the strong exciton-photon coupling in ZnO tapered whispering gallery (WG) microcavity at room temperature. By scanning excitations along the tapered arm of ZnO tetrapod using micro-photoluminescence spectrometer with different polarizations, we observed a transition from the pure WG optical modes in the weak interaction regime to the excitonic polariton in the strong coupling regime. The experimental observations are well described by using the plane wave model including excitonic polariton dispersion relation. This provides a direct mapping of the polariton dispersion, and thus a comprehensive picture for coupling of different excitons with differently polarized WG modes., 16 pages, 3 figures, 1 table

In the absence of any external applied magnetic field, we have found that a magnetic tunnel junction (MTJ) can produce a significant output direct voltage under microwave radiation at frequencies, which are far from the ferromagnetic resonance condition, and this voltage signal can be increase by at least an order of magnitude by applying a direct current bias. The enhancement of the microwave detection can be explained by the nonlinear resistance/conductance of the MTJs. Our estimation suggests that optimized MTJs should achieve sensitivities for non-resonant broadband microwave detection of about 5,000 mV/mW.