Long-range Coupling Research Articles

Embedding atomic cobalt into graphene lattices to activate room-temperature ferromagnetism

Graphene is extremely promising for next-generation spintronics applications; however, realizing graphene-based room-temperature magnets remains a great challenge. Here, we demonstrate that robust room-temperature ferromagnetism with TC up to ∼400 K and saturation magnetization of 0.11 emu g−1 (300 K) can be achieved in graphene by embedding isolated Co atoms with the aid of coordinated N atoms. Extensive structural characterizations show that square-planar Co-N4 moieties were formed in the graphene lattices, where atomically dispersed Co atoms provide local magnetic moments. Detailed electronic structure calculations reveal that the hybridization between the d electrons of Co atoms and delocalized pz electrons of N/C atoms enhances the conduction-electron mediated long-range magnetic coupling. This work provides an effective means to induce room-temperature ferromagnetism in graphene and may open possibilities for developing graphene-based spintronics devices.

Spreading of correlations and entanglement in the long-range transverse Ising chain

Whether long-range interactions allow for a form of causality in non-relativistic quantum models remains an open question with far-reaching implications for the propagation of information and thermalization processes. Here, we study the out-of-equilibrium dynamics of the one-dimensional transverse Ising model with algebraic long-range exchange coupling. Using a state of the art tensor-network approach, complemented by analytic calculations and considering various observables, we show that a weak form of causality emerges, characterized by non-universal dynamical exponents. While the local spin and spin correlation causal edges are sub-ballistic, the causal region has a rich internal structure, which, depending on the observable, displays ballistic or super-ballistic features. In contrast, the causal region of entanglement entropy is featureless and its edge is always ballistic, irrespective of the interaction range. Our results shed light on the propagation of information in long-range interacting lattice models and pave the way to future experiments, which are discussed.

Critical behavior and anisotropic magnetocaloric effect of the quasi-one-dimensional hexagonal ferromagnet PrCrGe3

Critical properties and anisotropic magnetocaloric effect of hexagonal ferromagnet $\mathrm{Pr}\mathrm{Cr}{\mathrm{Ge}}_{3}$ single crystals were investigated. The critical exponents $\ensuremath{\beta}=0.352$ with a critical temperature ${T}_{C}=90.5\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ and $\ensuremath{\gamma}=1.026$ with ${T}_{C}=90.6\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ are obtained by the modified Arrott plot, whereas $\ensuremath{\delta}=3.98$ is deduced by a critical isotherm analysis. The critical exponents suggest a long-range magnetic coupling with the exchange distance decaying as $J(r)\ensuremath{\sim}{r}^{\ensuremath{-}4.6}$. Furthermore, the magnetic entropy change $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}$ reaches a maximum value around ${T}_{C}$, i.e., $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}\ensuremath{\sim}3.2(1.8)\phantom{\rule{0.28em}{0ex}}\mathrm{J}\phantom{\rule{0.28em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ with in-plane (out-of-plane) field change of 5 T, verifying large magnetic anisotropy. The rescaled $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}(T,H)$ plots collapse onto a universal curve independent of temperature and field, confirming a second-order magnetic phase transition and reliability of the obtained critical exponents.

Edge states enhanced by long-range hopping: An analytical study* *Project supported by the National Natural Science Foundation of China (Grant No. 11847061) and the Startup Program of Shanghai University of Engineering Science.

We analyze the behavior of edge states in long-range (LR) interacting systems. In terms of lattice model Hamiltonian with the LR coupling, we determine analytically the condition of existence of edge states within the transfer matrix method (TMM). The expressions we obtain are general and hold for any choice of the LR hopping. The reason why edge states can appear is the transfer matrix in the bulk different from that in the boundary layers. Our predictions are in good agreement with numerical results by exact diagonalization. Our result is helpful in solving novel edge states in one- and two-dimensional (2D) superconductors with LR hopping and pairing.

Synthesis and structural elucidation of a series of isoflavones-based on FPR antagonists

Synthesis and structural elucidation of a series of isoflavones-based on FPR antagonists

Lipopolysaccharide transport involves long-range coupling between cytoplasmic and periplasmic domains of the LptB2FGC extractor.

The cell surface of the Gram-negative cell envelope contains lipopolysaccharide (LPS) molecules, which form a permeability barrier against hydrophobic antibiotics. The LPS transport (Lpt) machine composed of LptB2FGCADE forms a proteinaceous trans-envelope bridge that allows for the rapid and specific transport of newly synthesized LPS from the inner membrane (IM) to the outer membrane (OM). This transport is powered from the IM by the ATP-binding cassette transporter LptB2FGC. The ATP-driven cycling between closed- and open-dimer states of the ATPase LptB2 is coupled to the extraction of LPS by the transmembrane domains LptFG. However, the mechanism by which LPS moves from a substrate-binding cavity formed by LptFG at the IM to the first component of the periplasmic bridge, the periplasmic β-jellyroll domain of LptF, is poorly understood. To better understand how LptB2FGC functions in Escherichia coli, we searched for suppressors of a defective LptB variant. We found that defects in LptB2 can be suppressed by both structural modifications to the core oligosaccharide of LPS and changes in various regions of LptFG, including a periplasmic loop in LptF that connects the substrate-binding cavity in LptFG to the periplasmic β-jellyroll domain of LptF. These novel suppressors suggest that interactions between the core oligosaccharide of LPS and periplasmic regions in the transporter influence the rate of LPS extraction by LptB2FGC. Together, our genetic data reveal a path for the bi-directional coupling between LptB2 and LptFG that extends from the cytoplasm to the entrance to the periplasmic bridge of the transporter.IMPORTANCEGram-negative bacteria are intrinsically resistant to many antibiotics due to the presence of lipopolysaccharide (LPS) at their cell surface. LPS is transported from its site of synthesis at the inner membrane to the outer membrane by the Lpt machine. Lpt proteins form a transporter that spans the entire envelope and is thought to function similarly to a PEZ candy dispenser. This trans-envelope machine is powered by the cytoplasmic LptB ATPase through a poorly understood mechanism. Using genetic analyses in Escherichia coli, we found that LPS transport involves long-ranging bi-directional coupling across cellular compartments between cytoplasmic LptB and periplasmic regions of the Lpt transporter. This knowledge could be exploited in developing antimicrobials that overcome the permeability barrier imposed by LPS.

Paramagnetism of carbyne nanocrystals

In terms of carbon-atom hybridization, well-established forms of carbon are diamond with three-dimensional sp3-hybridization and graphite with two-dimensional sp2-hybridization which have been known as the first and second carbons and utilized for millennia. In fact, there is the third carbon with one-dimensional sp-hybridization, i.e. so-called carbyne. Recently, nanocrystals of the third carbon have been synthesized in the laboratory and they are called white carbon because these synthesized carbyne nanocrystals (CNCs) look white powders. Here, for the first time, the paramagnetism of CNCs is reported. Experimental observations show notable paramagnetism but no magnetic ordering at any given temperature. The moment concentration is estimated to be one moment per approximately 10,000 carbon atoms. These magnetic moments are probably originated from the collective magnetism phenomenon, which is attributed to hydrogen atom adsorbed on the carbon chain and vacancy in CNCs according to density functional theory-based first principle calculations. The localized defect wave favors a spin-polarized ground state and forms a local magnetic moment, promoting a long-range magnetic coupling between local magnetic moment, finally, results in a collective magnetism. This understanding about magnetism and its origin in the sp-hybridized carbon material can be instructive to interpretation of magnetism of other carbon allotropes.

Long-Range Coupling between Kinesins Regulates Collective Motor Behavior

Coupling of motor proteins within large arrays drives muscle contraction, flagellar beating, chromosome segregation, and other biological processes. Short-range interaction mechanisms of motor coupling, such as steric crowding and mechanical linkage, have been well-studied. However, coupling mechanisms that act at longer length scales remain largely unexplored. Here we report evidence of long-range motor-motor coupling on microtubules at picomolar protein concentration, where short-range motor interactions are unlikely.

Long-Distance Ultrafast Spin Transfer over a Zigzag Carbon Chain Structure.

Using high-level abinitio quantum theory we suggest an optically induced subpicosecond spin-transfer scenario over 4.428nm, a distance which is directly comparable to the actual CMOS scale. The spin-density transfer takes place between two Ni atoms and over a 40-atom-long zigzag carbon chain. The suitable combination of the local symmetries of the participating carbon atoms and the global symmetry of the whole molecule gives rise to what we term the dynamical Goodenough-Kanamori rules, allowing the long-range coupling of the two Ni atoms. We also present local spin-flip scenarios, and compare spin flip and spin transfer with respect to their sensitivity against an external static magnetic gradient. Finally, we use two identical laser pulses, rather than a single one, which allows us to accurately control local (intrasite) vs global (intersite) processes, and we thus solve the problem of embedding individually addressable molecular nanologic elements in an integrated nanospintronic circuit. Our results underline the great potential of carbon chain systems as building and supporting blocks for designing future all-optical magnetic processing units.

Spin-wave dispersion and exchange stiffness in Nd2Fe14B and RFe11Ti ( R=Y,Nd,Sm ) from first-principles calculations

We theoretically investigate spin-wave dispersion in rare-earth magnet compounds by using first-principles calculations and a method we call the reciprocal-space algorithm (RSA). The value of the calculated exchange stiffness for Nd$_2$Fe$_{14}$B is within the range of reported experimental values. We find that the exchange stiffness is considerably anisotropic when only short-range exchange couplings are considered, whereas inclusion of long-range couplings weakens the anisotropy. In contrast, $R$Fe$_{11}$Ti ($R$=Y, Nd, Sm) shows large anisotropy in the exchange stiffness.

Kinetics of the two-dimensional long-range Ising model at low temperatures.

We study the low-temperature domain growth kinetics of the two-dimensional Ising model with long-range coupling J(r)∼r^{-(d+σ)}, where d=2 is the dimensionality. According to the Bray-Rutenberg predictions, the exponent σ controls the algebraic growth in time of the characteristic domain size L(t),L(t)∼t^{1/z}, with growth exponent z=1+σ for σ<1 and z=2 for σ>1. These results hold for quenches to a nonzero temperature T>0 below the critical temperature T_{c}. We show that, in the case of quenches to T=0, due to the long-range interactions, the interfaces experience a drift which makes the dynamics of the system peculiar. More precisely, we find that in this case the growth exponent takes the value z=4/3, independently of σ, showing that it is a universal quantity. We support our claim by means of extended Monte Carlo simulations and analytical arguments for single domains.

Various effects induced by local synchronization in neural networks

In the cerebral cortex, the large-scale synchronous firing of neurons can cause epilepsy, during which spiral waves can spontaneously occur. The relationship between the synchronous firing of a large number of neurons and the spontaneous generation of spiral waves is still unclear. In this paper, a two-dimensional neuronal network with the long-range coupling regions generated by adding long-range horizontal connections is constructed. The Morris-Lecar neuron model is used to study the propagation of waves in the two-dimensional neuronal network with the rectangular long-range coupling regions. Numerical simulation results show that the plan and target waves whose propagation directions are both parallel to that of the long-range coupling can lead the neurons to be excited synchronously in the long-range coupling region. This synchronous firing is accompanied by delayed firing of some neurons and premature firing of others. When the width of the long-range coupling region exceeds the critical width, all the neurons in the long-range coupling region delay firing. When the width of the long-range coupling region exceeds a maximum conduction width, the waves will not pass through the long-range coupling region. When the size of the rectangular region of the long-range coupling is selected appropriately, the synchronous excitation of neurons can cause network to present the backfiring effect and to have the selectivity of wave propagation direction. Furthermore, the selectivity of wave propagation direction is very sensitive to whether the neuron is in the stationary state and also to the change of coupling strength, so that the high frequency plane wave train can partially pass through the long-range coupling region whose width exceeds the maximum conduction width. So we can control whether the wave can pass through the long-range coupling region of a certain width by giving the neurons in the long-range coupling region a tiny perturbation. When one or two long-range coupling regions are constructed in the neural network and the size of the long-range coupling regions is selected appropriately, the self-sustaining plane wave, spiral wave and target wave can appear spontaneously in the network when the wave passes through the long-range coupling regions. The physical mechanisms behind those phenomena are also analyzed.

Chimeras on a social-type network

We consider a social-type network of coupled phase oscillators. Such a network consists of an active core of mutually interacting elements, and of a flock of passive units, which follow the driving from the active elements, but otherwise are not interacting. We consider a ring geometry with a long-range coupling, where active oscillators form a fluctuating chimera pattern. We show that the passive elements are strongly correlated. This is explained by negative transversal Lyapunov exponents.

Long-range exciton diffusion in a non-fullerene acceptor: approaching the incoherent limit

Low energetic disorder enables the accurate and high-speed prediction of exciton diffusion parameters in a non-fullerene acceptor.

A novel o-vanillin Fe(III) complex catalytically active in C-H oxidation: exploring the magnetic exchange interactions and spectroscopic properties with different DFT functionals.

The novel complex [FeIIICl(L)2(H2O)] (1) was synthesized by interaction of iron(III) chloride with ethanol solution of o-vanillin (HL) and characterized by IR, UV/Vis spectroscopy, thermogravimetry and single crystal X-ray diffraction analysis. The molecules of 1 in the solid state are joined into supramolecular dimeric units, where a set of strong hydrogen bonds predefines the structure of the dimer according to the "key-lock" principle. From the Hirshfield surface analysis the contribution of π⋯π stacking to the overall stabilization of the dimer was found to be negligible. Broken symmetry DFT calculations suggested the presence of long-range antiferromagnetic interactions (J = -0.12 cm-1 for H = -JS1S2 formalism) occurring through the Fe-O⋯O-Fe pathway, as evidenced by the studies of the model dimers where the water molecules were substituted by acetonitrile and acetone ones. The benchmark studies using a set of literature examples and various DFT functionals revealed the hybrid-GGA B3LYP as the best one for prediction of FeIII⋯FeIII antiferromagnetic exchange couplings of small magnitude. Magnetic susceptibility measurements confirmed antiferromagnetic coupling between the metal atoms in 1 with a coupling constant of -0.35 cm-1. Catalytic studies demonstrated that 1 acts as an efficient catalyst in the oxidation of cyclohexane with hydrogen peroxide in the presence of nitric acid promoter and under mild conditions (yield up to 37% based on the substrate), while tert-butylhydroperoxide (TBHP) and m-chloroperoxybenzoic acid (m-CPBA) as oxidants exhibit less efficiency. Combined UV/TDDFT studies evidence the structural rearrangement of 1 in acetonitrile with the formation of [FeIIICl(L)2(CH3CN)] species. The TDDFT benchmark using nine common DFT functionals and two model compounds (o-vanillin and [FeIII(H2O)6]3+ ion) support the hybrid meta-GGA M06-2X functional as the one most correctly predicting the excited state structure for the Fe(III) complexes, under the conditions studied.

Local inspection of magnetic properties in GdMnIn by measuring hyperfine interactions

GdMnIn is reported to crystallize in the hexagonal MgNi2-type structure presenting a spin-glass behavior with no magnetic order attributed to the triangular spin frustration of magnetic ions. In the present work, FC-ZFC magnetization, specific heat and AC susceptibility measurements along with the local magnetic exchange measured by hyperfine interactions at In sites are used to investigate the magnetic behavior in GdMnIn compound. The ZFC-FC magnetization curves exhibit an inflection which was ascribed to the antiferromagnetic transition at TN= 145 K. These curves also give an indication of thermomagnetic irreversibility at 118 K, which along with the absence of inflection in specific heat results might be associated to spin-glass behavior. Results of AC susceptibility and magnetic hyperfine field measured using 111In(111Cd) probe nuclei carried out by perturbed angular correlations (PAC) technique did not show evidence of spin-glass behavior. The thermomagnetic irreversibility in FC-ZFC curves along with results of hyerfine interactions suggest the presence of magneto-crystalline anisotropy effects and a weak long-range coupling in GdMnIn.

Heterotropic Roles of Divalent Cations in the Establishment of Allostery and Affinity Maturation of Integrin αXβ2

SummaryAllosteric activation and silencing of leukointegrins transpire through highly complex structural changes between and within domains, mediating integrin affinity and bidirectional allostery relay. However, the landscape of these conformational changes, which is essential for elaborating integrin dynamics on cell surfaces and designing leukointegrin specific small molecules, has not yet been mapped. Herein we combine biophysical approaches and cell-based affinity assays to fine-tune the conformational dynamism and adhesiveness of a leukocyte integrin, αXβ2, using its physiological cofactor Mg2+. Stepwise addition of Mg2+ revealed two mutually coupled events for the αXβ2 ligand-binding domain—called the αX I-domain—corresponding to allostery establishment and affinity maturation. Electrostatic alterations in the statistically co-evolved Mg2+-binding site establish long-range couplings, leading to pH and Mg2+-occupancy dependent bimodal stability change in the αX I-domain fold. The ligand-binding sensorgrams revealed composite affinity events for the αX I-domain accounting for the multiplicity of conformational states existing in the solution. This bi-faceted transition appears to progressively amalgamate the adhesiveness and allostery within the structural interconversion zone. This work highlights how the intrinsically flexible architecture endows a dynamic continuum to the αI-domain structure on the intact integrin platform, thereby progressively regulating allostery establishment and affinity maturation. This dynamic characteristic appears as a specialization of the αX I-domain and is consistent with its rapid equilibration between open and closed conformations, facilitating rapid upregulation of leukocyte adhesiveness and activation.

Cosmosporasides F–H, three new sugar alcohol conjugated acyclic sesquiterpenes from a Fusarium oxysporum fungus

Three new sugar alcohol conjugated acyclic sesquiterpenes, cosmosporasides F–H (1–3), were isolated from the fermented cultures of Fusarium oxysporum SC0002. Their structures were elucidated by extensive analysis of spectroscopic data, including 1H−13C long-range coupling constants (J C,H). Their antibacterial, cytotoxic and anti-inflammatory activities were evaluated.

Quasi-many-body localization of interacting fermions with long-range couplings

A number of experimental platforms for quantum simulations of disordered quantum matter, from dipolar systems to trapped ions, involve degrees of freedom which are coupled by power-law decaying hoppings or interactions, yet the interplay of disorder and interactions in these systems is far less understood than in their short-ranged counterpart. Here we consider a prototype model of interacting fermions with disordered long-ranged hoppings and interactions, and use the flow equation approach to map out its dynamical phase diagram as a function of hopping and interaction exponents. We demonstrate that the flow equation technique is ideally suited to problems involving long-range couplings due to its ability to accurately simulate very large system sizes. We show that, at large on-site disorder and for short-range interactions, a transition from a delocalized phase to a quasi many-body localized (MBL) phase exists as the hopping range is decreased. This quasi-MBL phase is characterized by intriguing properties such as a set of emergent conserved quantities which decay algebraically with distance. Surprisingly we find that a crossover between delocalized and quasi-MBL phases survives even in the presence of long-range interactions.

Magnesium Contact Ions Stabilize the Tertiary Structure of Transfer RNA: Electrostatics Mapped by Two-Dimensional Infrared Spectra and Theoretical Simulations.

Ions interacting with hydrated RNA play a central role in defining its secondary and tertiary structure. While spatial arrangements of ions, water molecules, and phosphate groups have been inferred from X-ray studies, the role of electrostatic and other noncovalent interactions in stabilizing compact folded RNA structures is not fully understood at the molecular level. Here, we demonstrate that contact ion pairs of magnesium (Mg2+) and phosphate groups embedded in local water shells stabilize the tertiary equilibrium structure of transfer RNA (tRNA). Employing dialyzed tRNAPhe from yeast and tRNA from Escherichia coli, we follow the population of Mg2+ sites close to phosphate groups of the ribose-phosphodiester backbone step by step, combining linear and nonlinear infrared spectroscopy of phosphate vibrations with molecular dynamics simulations and ab initio vibrational frequency calculations. The formation of up to six Mg2+/phosphate contact pairs per tRNA and local field-induced reorientations of water molecules balance the phosphate–phosphate repulsion in nonhelical parts of tRNA, thus stabilizing the folded structure electrostatically. Such geometries display limited sub-picosecond fluctuations in the arrangement of water molecules and ion residence times longer than 1 μs. At higher Mg2+ excess, the number of contact ion pairs per tRNA saturates around 6 and weakly interacting ions prevail. Our results suggest a predominance of contact ion pairs over long-range coupling of the ion atmosphere and the biomolecule in defining and stabilizing the tertiary structure of tRNA.