Exotic Coupling Research Articles

Temporally deuterogenic plasmonic vortices.

Over the past decade, orbital angular momentum has garnered considerable interest in the field of plasmonics owing to the emergence of surface-confined vortices, known as plasmonic vortices. Significant progress has been made in the generation and manipulation of plasmonic vortices, which broadly unveil the natures of plasmonic spin-orbit coupling and provide accessible means for light-matter interactions. However, traditional characterizations in the frequency domain miss some detailed information on the plasmonic vortex evolution process. Herein, an exotic spin-orbit coupling phenomenon is demonstrated. More specifically, we theoretically investigated and experimentally verified a temporally deuterogenic vortex mode, which can be observed only in the time domain and interferes destructively in the intensity field. The spatiotemporal evolution of this concomitant vortex can be tailored with different designs and incident beams. This work extends the fundamental understanding of plasmonic spin-orbit coupling and provides a unique optical force manipulation strategy, which may fuel plasmonic research and applications in the near future.

Creation of galaxy-shaped vortex relief structures in azo-polymers with petal-like beams.

We demonstrate the formation of surface relief structures in azo-polymers which exhibit multiple spiral arms, through irradiation of a rotating petal-like beam formed by the coherent superposition of Laguerre-Gaussian modes with opposite handedness. Intriguingly, the fabricated relief structures reflect full geometric parameters of the irradiated petal beam, such as handedness, topological charge, initial azimuthal phase and even ellipticity, corresponding to azimuthal and polar angles along equator and meridian planes of an orbital Poincaré sphere. The handedness, or direction of rotation, of the fabricated structures with multiple spiral arms could be controlled via the rotation and polarization directions of the irradiating laser field. This effect highlights an exotic coupling between the optical intensity gradient induced mass transport of the irradiated material and the spin angular momentum characteristics of the irradiating optical field. The azimuthal orientation of the surface relief structures could also be tuned by altering the initial relative phase between the coherently superposed Laguerre-Gaussian modes with opposite handedness, constituting the irradiating petal laser field. This work offers new insights into fundamental interactions which occur between light and matter, and we believe, will pave the way towards advanced technologies, such as ultrahigh density optical data storage.

Spin reorientation and magnetodielectric anomalies in FexO1+x (x = 2,3) thin films-effect of microwave radiations

Materials with remarkable magnetodielectric properties are promising candidates for multifunctional devices. Microwave assisted sol-gel method is adopted to synthesize iron oxide thin films under microwave irradiations of 180 W-1000 W. Ferromagnetic response of sols is observed at 360–450 W, 630 W and 720 W powers, while superparamagnetic behavior is obtained at 810 W-1000 W. Films prepared using sols synthesized at 180 W, 270 W and 540 W exhibit amorphous nature. α-Fe2O3 phase is observed at microwave power (MW) of 360 W-450 W. γ-Fe2O3 phase is observed at MW of 630 W and 720 W and Fe3O4 phase is observed at 810–1000 W. Highest saturation magnetization of 45.23emu/cm3, 248.403emu/cm3 and 419.43emu/cm3are observed for α-Fe2O3, γ-Fe2O3 and Fe3O4, respectively. The transition of Verwey in Fe3O4 thin film is observed at ∼ 115.2 K, whereas γ-Fe2O3 phase does not show any such variation. Further, α-Fe2O3 phase show spontaneous magnetization at low temperatures from FC/ZFC curves. Highest dielectric constant of ∼ 54.26, 84.19 and 121.34 (log f = 5.0) are observed for α-Fe2O3, γ-Fe2O3 and Fe3O4, respectively. Magnetodielectric coupling (MDE) of ∼ −3.9%, −5.1% and −7.5% is obtained for α-Fe2O3, γ-Fe2O3 and Fe3O4 thin films. Fe3O4 phase is found to exhibit peculiar MDE coupling with respect to other phases, revealing exotic magnteodielectric coupling anomalies.

Exotic Coupling Between Plasmonic Nanoparticles Through Geometric Configurations

Coupled plasmonic systems are of great interest and have many applications such as information processing and sensing. By choosing proper geometric configurations of coupled plasmonic systems, one can obtain various optical properties. However, some interesting and important effects could not be described by earlier methods. We develop an improved method for coupled plasmonic nanoparticle systems that maps geometric configurations to optical properties more accurately. With the improved method, we realize a low-loss cavity of metallic nanoparticles through a proper geometric configuration, and we find a limit to the loss in the metallic nano-cavity. We also use this method to realize an exceptional point and exceptional nexus in a hybrid plasmonic system. Finally, we predict asymmetric coupling, which leads to chirality and directional energy transfer.

Searching for lepton portal dark matter with colliders and gravitational waves

We study the lepton portal dark matter (DM) model in which the relic abundance is determined by the portal coupling among the Majorana fermion DM candidate χ, the singlet charged scalar mediator S± and the Standard Model (SM) right-handed lepton. The direct and indirect searches are not sensitive to this model. This article studies the lepton portal coupling as well as the scalar portal coupling (between S± and SM Higgs boson), as the latter is generally allowed in the Lagrangian. The inclusion of scalar portal coupling not only significantly enhances the LHC reach via the gg → h* → S+S− process, but also provides a few novel signal channels, such as the exotic decays and coupling devi- ations of the Higgs boson, offering new opportunities to probe the model. In addition, we also study the Drell-Yan production of S+S− at future lepton colliders, and find out that the scenario where one S± is off-shell can be used to measure the lepton portal coupling directly. In particular, we are interested in the possibility that the scalar potential triggers a first-order phase transition and hence provides the stochastic gravitational wave (GW) signals. In this case, the terrestrial collider experiments and space-based GW detectors serve as complementary approaches to probe the model.

Role of compensating current in the weak Josephson coupling regime: An extended study on excitonic Josephson junctions

Huang's experiment [Phys. Rev. Lett. $\bf 109$, 156802 (2012)] found, in the quantum Hall bilayer of the Corbino geometry, the interlayer tunneling currents at two edges are coupled to each other and one of two tunneling currents is referred to as the compensating current of the other. Our another work[arXiv:2006.15329] has explained this exotic coupling phenomenon as a result of excitonic Josephson effect induced by interlayer tunneling current. In this paper, we study the same setup -- excitonic Josephson junction -- but in the weak Josephson coupling regime, which occurs for large junction length. Interestingly, we find the compensating current drives the other edge to undergo a nonequilibrium phase transition from a superfluid to resistive state, which is signaled by an abrupt jump of the critical tunneling current. We also identify the critical exponent and furthermore offer more experimental prediction.

Quantum simulations of light-matter interactions in arbitrary coupling regimes

Light-matter interactions are an established field that is experiencing a renaissance in recent years due to the introduction of exotic coupling regimes. These include the ultrastrong and deep-strong coupling regimes, where the coupling constant is smaller and of the order of the frequency of the light mode, or larger than this frequency, respectively. In the past few years, quantum simulations of light-matter interactions in all possible coupling regimes have been proposed and experimentally realized, in quantum platforms such as trapped ions, superconducting circuits, cold atoms, and quantum photonics. We review this fledgling field, illustrating the benefits and challenges of the quantum simulations of light-matter interactions with quantum technologies.

Magneto-luminescent zinc/iron oxide core-shell nanoparticles with tunable magnetic properties

Abstract Core-shell nanospheres with tailorable magnetic properties and strong luminescence promise versatile and efficient biomedical and electronic applications. We report a low-cost sonochemical synthesis of ZnO/iron oxide core-shell nanostructures with tunable magnetic properties. The high-resolution transmission electron microscopy (HRTEM) illustrates the distinguished dispersity of the oxide nanoparticles, whereas elemental profiling using line scan data confirm the formation of the distinguished core and shell phases. Annealing in N2–H2 and Ar–H2 ambient alters the magnetic properties such as coercive field, saturation magnetization, and remnant magnetization within the inverse spinel iron oxide with space group Fd3m. Subtle structural changes between maghemite (γ-Fe2O3) and its reduced form, magnetite (Fe3O4), have been identified in the thin (0.5–3 nm) shell region of atomic dimensions. Structural composition including phase transitions and defect states are investigated using XRD, XPS, and Raman measurements. Coexistence of ferromagnetism (from the shell and characterized by magnetic measurements) and strong luminescence (from ZnO core and obtained from photoluminescence spectroscopy) at room temperature indicates exotic magneto-optical coupling, which is supported by the blue-shifted luminescence spectra. Our approach combining nanotechnology and solid-state chemistry opens a new frontier to the building of innovative nanomaterials for integration, especially multifunctional core-shell oxide nanomaterials.

Constraints on a Spin-Dependent Exotic Interaction between Electrons with Single Electron Spin Quantum Sensors.

A new laboratory bound on the axial-vector mediated interaction between electron spins at micrometer scale is established with single nitrogen-vacancy (NV) centers in diamond. A single crystal of p-terphenyl doped pentacene-d_{14} under laser pumping provides the source of polarized electron spins. Based on the measurement of polarization signal via nitrogen-vacancy centers, we set a constraint for the exotic electron-electron coupling g_{A}^{e}g_{A}^{e}, within the force range from 10 to 900 μm. The obtained upper bound of the coupling at 500 μm is |g_{A}^{e}g_{A}^{e}/4πℏc|≤1.8×10^{-19}, which is one order of magnitude more stringent than a previous experiment. Our result shows that the NV center can be a promising platform for searching for new particles predicted by theories beyond the standard model.

Progress and prospects of aberration-corrected STEM for functional materials

Aberration-corrected scanning transmission electron microscopy (STEM) provides real space imaging and spectroscopy at atomic resolution with a new level of sensitivity to structure, bonding, elemental valence and even dynamics. It has developed into the most powerful characterization and even fabrication platform for all materials, especially for functional materials with complex structural features that dynamically respond to external fields. Several representative examples of functional materials are shown, including piezoelectric and photoelectric materials, functional oxide interfaces, metal–organic framework (MOF)-derived transition metal oxide/phosphide catalysts and two-dimensional (2D) materials. In piezoelectric systems, atomic-resolution polarization mapping by Z-contrast imaging shows the intimate coexistence of two ferroelectric phases inside nanodomains. Quantitative STEM imaging and EELS spectroscopy reveal the underlying mechanism of the exotic coupling between polarization and charge at a functional oxide interface. Under the low-voltage STEM, defects in 2D materials are clearly visible, for example novel edges and single atom dopants. The dynamic behavior of single atoms in vacancies of monolayer MoS2 is shown to highlight the electron-beam induced nanofabrication ability of aberration-corrected STEM. Thanks to the rapid development of segmented/pixelated detectors, differential phase contrast and 4D STEM techniques are promising for the near future, providing more opportunities to understand the link between structure and functionality.

Exotic Elko on string-like defects in six dimensions

We analyse the trapping of eigenspinors of the charge conjugation operator with dual helicity (Elko), in thin and thick string-like models with codimension-2. Elko spinor fields describe mass-dimension-one fermions in four dimensions (and, correspondingly, mass-dimension-two fermions in six dimensions), that represent natural dark-matter prime candidates. This dark spinor has many applications, from particle physics to cosmology. On the other hand, six-dimensional brane-world models have, among other prominent features, the spontaneous confinement of free spin-1 fields and a mechanism that explains the mass hierarchy of fundamental fermions. In this paper, we use scalar couplings in order to confine the zero mode of Elko in six dimensions. Moreover, we use the Elko dark-spinor features to propose an exotic coupling in order to remove the complex-valued terms in the massive Kaluza-Klein modes. Hence, we show that six-dimensional models can resolve the main issues of Elko fields confinement presented in five dimensions.

Way-out to the gravitino problem in intersecting D-brane Pati–Salam models

We discuss the gravitino problem in the context of the exotic see-saw mechanism for neutrinos and leptogenesis, UV completed by intersecting D-branes Pati–Salam models. In the exotic see-saw model, supersymmetry is broken at high scales M[Formula: see text] 109 GeV and this seems in contradiction with gravitino bounds from inflation and baryogenesis. However, if gravitino is the lightest stable supersymmetric particle, it will not decay into other SUSY particles, avoiding the gravitino problem and providing a good cold dark matter (CDM). Gravitini are super heavy dark particles and they can be produced by non-adiabatic expansion during inflation. Intriguingly, from bounds on the correct abundance of dark matter (DM), we also constrain the neutrino sector. We set a limit on the exotic instantonic coupling of [Formula: see text] 10[Formula: see text]–10[Formula: see text]. This also sets constrains on the Calabi–Yau compactifications and on the string scale. This model strongly motivates very high energy DM indirect detection of neutrini and photons of 10[Formula: see text]–10[Formula: see text] GeV: gravitini can decay on them in a cosmological time because of soft R-parity breaking effective operators.

Anisotropic symmetric exchange as a new mechanism for multiferroicity

Discovering new magnetoelectric multiferroics is an exciting research area. Very recently, a collinear antiferromagnetic spin order was found to induce a ferroelectric polarization in a highly symmetric cubic perovskite ${\mathrm{LaMn}}_{3}{\mathrm{Cr}}_{4}{\mathrm{O}}_{12}$. This spin-driven ferroelectricity could not be explained by any of the existing multiferroic models. Here, we put forward a new model, i.e., anisotropic symmetric exchange, to understand this phenomenon, which was confirmed by density functional calculations and tight-binding simulations. Furthermore, our perturbation analysis shows that the anisotropic symmetric exchange term can be even stronger than the conventional contributions in some $5d$ systems. Our multiferroic model can not only explain the experimental results, but also may open a new avenue for exploring exotic magnetoelectric coupling effects.

Alya: Multiphysics engineering simulation toward exascale

Alya is a multi-physics simulation code developed at Barcelona Supercomputing Center (BSC). From its inception Alya code is designed using advanced High Performance Computing programming techniques to solve coupled problems on supercomputers efficiently. The target domain is engineering, with all its particular features: complex geometries and unstructured meshes, coupled multi-physics with exotic coupling schemes and physical models, ill-posed problems, flexibility needs for rapidly including new models, etc. Since its beginnings in 2004, Alya has scaled well in an increasing number of processors when solving single-physics problems such as fluid mechanics, solid mechanics, acoustics, etc. Over time, we have made a concerted effort to maintain and even improve scalability for multi-physics problems. This poses challenges on multiple fronts, including: numerical models, parallel implementation, physical coupling models, algorithms and solution schemes, meshing process, etc. In this paper, we introduce Alya's main features and focus particularly on its solvers. We present Alya's performance up to 100.000 processors in Blue Waters, the NCSA supercomputer with selected multi-physics tests that are representative of the engineering world. The tests are incompressible flow in a human respiratory system, low Mach combustion problem in a kiln furnace, and coupled electro-mechanical contraction of the heart. We show scalability plots for all cases and discuss all aspects of such simulations, including solver convergence.

String Cosmological Solutions with O(d, d) Duality Symmetry and Matter Coupling

The duality properties of string cosmology model with negative energy matter are investigated by means of renormalization group equation, the cosmological solutions with exotic matter coupling are obtained in D = d + 1 dimensional space-time. These inflation-power solutions can describe accelerated and decelerated process in the early universe, and the duality solutions can be generated through O(d, d) transformations.

Iron isotope effect on Tc in optimally-doped (Ba,K)Fe2As2 (Tc = 38 K) and SmFeAsO1−y (Tc = 54 K) superconductors

We report the iron isotope effect on a transition temperature (Tc) in an optimally-doped (Ba,K)Fe2As2 (Tc=38K) and SmFeAsO1−y (Tc=54K) superconductors. In order to obtain the reliable isotope shift in Tc, twin samples with different iron isotope mass are synthesized in the same conditions (simultaneously) under high-pressure. We have found that (Ba,K)Fe2As2 shows an inverse iron isotope effect αFe=−0.18±0.03 while SmFeAsO1−y shows a small iron isotope effect αFe=−0.02±0.01, where the isotope exponent α is defined by Tc∼M−α (M is the isotopic mass). The results show that αFe changes in the iron-based superconductors depending on the system. The distinct iron isotope effects imply the exotic coupling mechanism in the iron-based superconductors.

Inverse Iron Isotope Effect on the Transition Temperature of the(Ba,K)Fe2As2Superconductor

We report that the (Ba,K)Fe(2)As(2) superconductor (transition temperature, T(c) approximately 38 K) has an inverse iron isotope coefficient alpha(Fe) = -0.18(3) (where T(c) approximately M(-alphaFe) and M is the iron isotope mass); i.e., the sample containing the large iron isotope mass depicts a higher T(c). Systematic inverse shifts in T(c) were clearly observed between the samples using three types of Fe isotopes ((54)Fe, natural Fe, and (57)Fe). This indicates the first evidence of the inverse isotope effect in high-T(c) superconductors. This anomalous mass dependence on T(c) implies an exotic coupling mechanism in Fe-based superconductors.

Syntheses, Crystal Structures, and Magnetic Properties of Nitronyl Nitroxide Triradicals Composed of Ground-State Singlet Biradicals and Monoradicals: Molecular Spin Clusters in the Crystal

We report X-ray crystal structures and magnetic properties of novel nitronyl nitroxide triradicals, p-triNN (1) and m-triNN (2), in which a ground-state singlet (S = 0) biradical with a π-conjugated phenol substituent and an S = 1/2 carboxyl-substituted monoradicals are united by σ-bonds of an ester bridge. It is found for both 1 and 2 that the exchange interactions J(σ) between the biradical and the monoradical moieties through the σ-bonds of the ester bridge are much smaller than those through the π-conjugation, J(π), within the biradical moieties. Thus, the inequivalent magnetic degrees of freedom, one from the biradical and the other from the monoradical moiety, are retained in a single molecule. X-ray crystallography and magnetic susceptibility of 1 indicate that an intermolecular antiferromagnetic exchange interaction between the biradical and the monoradical moieties gives a three-spin cluster. On the other hand, the triradical 2 is found to form a six-spin cluster, consisting of two sets of monoradical−biradical pairs in the crystal. The formation of the molecular spin clusters in 1 and 2 gives us the way of developing exotic spin coupling systems from σ-bonded π-oligoradicals carrying multiple magnetic degrees of freedom.

Right-handed neutrinos in low-energy neutrino–electron scattering

In this Letter a scenario admitting the participation of the exotic scalar coupling of the right-handed neutrinos in addition to the standard vector and axial couplings of the left-handed neutrinos in the weak interactions is considered. The research is based on the low-energy (νμe−) and (νee−) scattering processes. The main goal is to show how the presence of the right-handed neutrinos in the above processes changes the laboratory differential cross section in relation to the Standard Model prediction. Both processes are studied at the level of the four-fermion point interaction. Neutrinos are assumed to be polarized Dirac fermions and to be massive. In the laboratory differential cross section, the new interference term between the standard vector coupling of the left-handed neutrinos and exotic scalar coupling of the right-handed neutrinos appears which does not vanish in the limit of vanishing neutrino mass. This additional contribution, including information on the transverse components of neutrino polarization, generates the azimuthal asymmetry in the angular distribution of the recoil electrons. This regularity would be a signature of the presence of the right-handed neutrinos in the neutrino–electron scattering.

Boron isotope effect in superconducting MgB2.

We report the preparation method of and boron isotope effect for MgB2, a new binary intermetallic superconductor with a remarkably high superconducting transition temperature T(c)(10B) = 40.2 K. Measurements of both temperature dependent magnetization and specific heat reveal a 1.0 K shift in T(c) between Mg11B2 and Mg10B2. Whereas such a high transition temperature might imply exotic coupling mechanisms, the boron isotope effect in MgB2 is consistent with the material being a phonon-mediated BCS superconductor.