Toroidal moments in electromagnetic metamaterials

We report the development of a new type of metamaterials supporting resonantly induced toroidal moments, the importance of which has recently been recognized in solid state, nuclear and particle physics. Our aim is to create a classical electrodynamic system, such as toroidal metamaterial [1], that enhances the elusive toroidal moment and suppresses the background of conventional multipole excitations, thus allowing the direct observation of its contribution to optical activity, anisotropy, asymmetric transmission and the formation of negative index bands

Anapole nanolasers for mode-locking and ultrafast pulse generation

Nanophotonics is a rapidly developing field of research with many suggestions for a design of nanoantennas, sensors and miniature metadevices. Despite many proposals for passive nanophotonic devices, the efficient coupling of light to nanoscale optical structures remains a major challenge. In this article, we propose a nanoscale laser based on a tightly confined anapole mode. By harnessing the non-radiating nature of the anapole state, we show how to engineer nanolasers based on InGaAs nanodisks as on-chip sources with unique optical properties. Leveraging on the near-field character of anapole modes, we demonstrate a spontaneously polarized nanolaser able to couple light into waveguide channels with four orders of magnitude intensity than classical nanolasers, as well as the generation of ultrafast (of 100 fs) pulses via spontaneous mode locking of several anapoles. Anapole nanolasers offer an attractive platform for monolithically integrated, silicon photonics sources for advanced and efficient nanoscale circuitry

Ferrotoroidic ground state in a heterometallic {Cr^IIIDy^III<inf>6</inf>} complex displaying slow magnetic relaxation

© 2017 The Author(s). Toroidal quantum states are most promising for building quantum computing and information storage devices, as they are insensitive to homogeneous magnetic fields, but interact with charge and spin currents, allowing this moment to be manipulated purely by electrical means. Coupling molecular toroids into larger toroidal moments via ferrotoroidic interactions can be pivotal not only to enhance ground state toroidicity, but also to develop materials displaying ferrotoroidic ordered phases, which sustain linear magneto-electric coupling and multiferroic behavior. However, engineering ferrotoroidic coupling is known to be a challenging task. Here we have isolated a {CrIIIDyIII6} complex that exhibits the much sought-after ferrotoroidic ground state with an enhanced toroidal moment, solely arising from intramolecular dipolar interactions. Moreover, a theoretical analysis of the observed sub-Kelvin zero-field hysteretic spin dynamics of {CrIIIDyIII6} reveals the pivotal role played by ferrotoroidic states in slowing down the magnetic relaxation, in spite of large calculated single-ion quantum tunneling rates

Metamaterials: demonstrating toroidal moment in the frame of classical electrodynamics

We present electromagnetic metamaterials the resonant response of which cannot be attributed to the excitation of conventional magnetic or charge multipoles and can only be explained by the existence of the induced toroidal dipole

Silicon sacrificial layer technology for the production of 3D MEMS (EPyC process)

The EPyC process uses silicon sacrificial layer technology, which makes it possible to generate high volume sacrificial structures of up to 100 microns thickness. The biggest challenge is the rapid and complete removal of the 3D sacrificial structure at the end of the process. This paper examines and compares in detail two silicon dry etching methods to optimize a new silicon etching process for successful EPyC manufacturing

Multilayer micromechanics process with thick functional layers (EPyC40)

The EPyC process (Epi-Poly-Cycle) (by Robert Bosch GmbH) opens up unique opportunities for manufacturing complex 3D MEMS structures having high effectiveness in small space. EPyC40 is an EPyC process with up to 40 μm thick polysilicon layers and sacrificial silicon technique. For successful manufacturing a 40 μm EPyC the epitaxial polysilicon layer must be electrically and mechanically optimized. A vertical deep trench patterns the functional and sacrificial areas. A passivation must be deposited homogeneously and has to be tight and robust towards silicon-etching gases. For more than one cycle it is necessary to tailor the layer stress of the epitaxial polysilicon and the wafer-bow. The full process for stacking up 5 EPyC cycles with two 40 μm epitaxial polysilicon layers was investigated in detail. A true 3D MEMS device providing high z deflection by use of a vertical comb drive with 40 μm electrodes was built up successfully to prove the feasibility of the EPyC process

Toroidal dipolar response in a metamaterial

Toroidal multipoles are fundamental electromagnetic excitations different from those associated with the familiar charge and magnetic multipoles. They have been held responsible for parity violation in nuclear and particle physics, but direct evidence of their existence in classical electrodynamics has remained elusive. We report on the observation of a resonant electromagnetic response in an artificially engineered medium, or metamaterial, that cannot be attributed to magnetic or charge multipoles and can only be explained by the existence of a toroidal dipole. Our direct experimental evidence of the toroidal response brings attention to the often ignored electromagnetic interactions involving toroidal multipoles, which could be present in naturally occurring systems, especially at the macromolecule level, where toroidal symmetry is ubiquitous