Dyadic Greens function for a topological insulator stratified sphere

We construct the dyadic Greens functions (DGFs) for a topological insulator (TI) stratified sphere within the framework of axion electrodynamics. For these DGFs, the additional expansion coefficients are included to account for the axion coupling effect. With the application of these DGFs, we derive the formulation of light scattering from a dipole near a TI stratified sphere. In our numerical studies, we give three types of configurations (a metal-coated TI sphere, a metal-TI-metal-coated TI sphere and an alternating metal-TI stratified sphere) to investigate how the topological magneto-electric (TME) response of the TI sphere (shells) influences on the multipolar plasmonic resonance of the metal shells. For these types, the results show that the TME effect causes some modifications of the decay rate spectrum for an emitting dipole near a TI stratified sphere. For the multipolar resonances of the metal shells, it is observed that the TME-induced red-shifts for the bonding and lower order antibonding modes are found but those for the higher order antibonding modes are insignificant. In addition, for a metal-coated TI sphere, we take into account the effects of losses in the TI core of which the dielectric function is chosen to be the form of the bulk or five quintuple layers (5QL) slab and then the some modifications of the TME-induced decay rate spectrum are obviously suppressed. These phenomenological characteristics provide useful guidance to probing the TME effect via molecular fluorescence experiments

Electromagnetic Radiation from a Spherical Static Current Source Coupled to Harmonic Axion Field

The electromagnetic fields generated from a static current source on a spherical surface are calculated in the framework of axion electrodynamics to first order in the coupling parameter. Comparisons of the results are made with reference to various results obtained in conventional Maxwell electrodynamics, as well as previous results obtained for point magnetic dipole source coupled to harmonic axion fields. Distinct features from the results so obtained are highlighted for possible experimental probing of the axions via electromagnetic interactions. In particular, electromagnetic radiation from sources with strong magnetic field is studied which may enable the detection of a cosmic axion field from its interaction with objects like neutron stars

Topological Magnetoelectric Effect as Probed by Nanoshell Plasmonic Modes

Axion electrodynamics is applied to study the response of a plasmonic nanoshell with a core made of topological insulator (TI) materials. The electric polarizability of such a system is calculated in the long wavelength limit via the introduction of two scalar potentials satisfying the various appropriate boundary conditions. Our focus is on the topological magneto-electric effect (TME) as manifested in the coupled plasmonic resonances of the nanoshell. It is found that for a TI with broken time-reversal symmetry, such TME will lead to observable red-shifts in the coupled plasmonic modes, with more significant manifestation of such shifts for the bonding modes of a metallic nanoshell. It is speculated that such universal red-shift could be a manifestation of the fundamental dual symmetry as generalized for axion electrodynamics

Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018.

Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field

Electromagnetic Reciprocity in the Presence of Topological Insulators

Electromagnetic reciprocity is studied in the presence of topological insulators (TI) with application of axion electrodynamics for harmonic electromagnetic fields. The corresponding generalized Lorentz and Feld-Tai type lemmas are derived in terms of the axion coupling parameter, and their correlation to the conditional symmetry in source-observer coordinates for the various Green dyadics is established subjected to different types of boundary conditions. Possible application of the results to the probing of the topological magneto-electric effects from TI is discussed

Dipole Emission Characteristics Near a Topological Insulator Sphere Coated with a Metallic Nanoshell

Topological insulators (TI) are quantum states of (2D/3D) matter with an insulating interior but conducting edge/surface states, with these boundary conducting states being protected topologically by time-reversal symmetry. Composite materials of heavy atoms such as Bi2Te3 can be fabricated to show TI properties due to the strong intrinsic spin-orbit coupling of the electrons in these materials. Among the so many intriguing physical properties of these materials, their topological magneto-electric (TME) response is unique and has been studied intensively in the literature, leading to intriguing optical effects such as Faraday and Kerr rotations of incident polarized beams at THz frequencies, as recently observed in a series of ingenious experiments. In addition, nontrivial modifications from this TME in the optical reciprocity of propagating EM waves have also been studied in recent time. Aside from such TME effect on traveling electromagnetic (EM) waves, the corresponding effect on confined evanescent waves has also been studied in the literature. In particular, excitation of surface plasmons at an interface of a TI and a metal has been investigated and the effect has been found to be small depending on the square of the fine-structure constant. In a recent study, we have extended such plasmonic excitation to the geometry of a spherical metallic shell with a TI core, and have observed such TME effect to be relatively more significant for the low frequency bonding modes of the metal shell – leading to manifested red-shifts of these modes. Moreover, this previous study was limited to an incident far-field source and only the dipolar response of the metal-coated TI core has been considered. The goal of this paper is to extend our previous work, to the study of the TME on the near fields of the TI-metal core-shell system. We thus here consider a localized dipole emitter in the vicinity of such a metal-coated TI sphere and study how the emitting characteristics of the dipole are modified by the excitation of all orders of multipoles of the coated sphere. This problem with a dipole interacting with a TI sphere has been actively studied in the recent literature, but only limited to “bare” TI particles. Realistic experiments can be designed via fluorescence studies of molecules adsorbed to these coated particles similar to those performed with bare metallic nanoparticles, with an eye on further manifestation of the TME effects from the TI, as well as the possibility of employing such effects for the control of the emission properties of the molecules. Since we shall consider both the molecule-sphere distance and the size of the coated spheres are going to be small compared to the emission wavelengths of the molecule, we shall adopt a long-wavelength formulation of the problem and all the multipolar responses of the coated sphere can be accounted for from calculating the various polarizabilities of the system. In the previous study with a far-field source, scattering experiments were referred to which require all the four (electric-electric; electric-magnetic; magnetic-electric; and magnetic-magnetic) polarizabilities to be calculated. However, in our present study of near-field source in the long wavelength approximation, we will only need the electric-electric polarizability since the other three responses will only lead to higher order contributions when we study how the induced fields from the coated TI sphere will affect the source dipole