Analysis of the Chirality Effects on the Capacity of Wireless Communication Systems in the THz band

International audienceThe potentialities of Terahertz frequency band in the context of nano-scale communications are largely increasing, thanks to specific features that allow to overcome the issues related to the spectrum scarcity and capacity limitation. Apart from high molecular absorption and very high reflection loss that represent the main phenomena in Terahertz (THz) band, in this paper we investigate the chirality effects that affect the propagation medium, in the frequency range (4 − 10) THz. It is observed that in this interval the chiral parameter shows resonance peaks in specific frequencies. In this paper we investigate the channel capacity in a special medium affected by chirality effects, such as biomolecules, DNA chains, etc. Specifically, we analyze the signal propagation in a chiral medium where a Giant Optical Activity (GOA) is present. This effect is typical of the so-called chiral-metamaterials. Through simulation results we distinguish the behavior of a chirality-affected channel with GOA in Line-of-Sight and Non-Line-of-Sight propagations, assuming different power allocation techniques and also comparing the performance to the case of No GOA

Computing and communications for the software-defined metamaterial paradigm: a context analysis

Metamaterials are artificial structures that have recently enabled the realization of novel electromagnetic components with engineered and even unnatural functionalities. Existing metamaterials are specifically designed for a single application working under preset conditions (e.g., electromagnetic cloaking for a fixed angle of incidence) and cannot be reused. Software-defined metamaterials (SDMs) are a much sought-after paradigm shift, exhibiting electromagnetic properties that can be reconfigured at runtime using a set of software primitives. To enable this new technology, SDMs require the integration of a network of controllers within the structure of the metamaterial, where each controller interacts locally and communicates globally to obtain the programmed behavior. The design approach for such controllers and the interconnection network, however, remains unclear due to the unique combination of constraints and requirements of the scenario. To bridge this gap, this paper aims to provide a context analysis from the computation and communication perspectives. Then, analogies are drawn between the SDM scenario and other applications both at the micro and nano scales, identifying possible candidates for the implementation of the controllers and the intra-SDM network. Finally, the main challenges of SDMs related to computing and communications are outlined.Peer ReviewedPostprint (published version

Technological Applications of Porphyrins and Related Compounds: Spintronics and Micro-/Nanomotors

The vital role played by porphyrins in cells and their use in therapeutic processes are well known. More recently, the technological applications of porphyrins have attracted the attention of researchers. Porphyrins have the property of half-metallic material, i.e., molecules that can host transition metals making feasible the production of spin-polarized electronic states at different channels. Therefore, porphyrins and hemeproteins are among the materials that have spin-filtering property to be applied in spintronics. Molecular spintronics is an emerging and highly relevant field due to their applications to the development of high-capacity information-storage devices and quantum computers. The catalytic properties of porphyrins and related compounds such as the hemeproteins are also applicable in the fabrication of micro-/nanomotors (MNMs). In this chapter, we describe the advances and future perspectives in the technological applications of porphyrins and related compounds in spintronic devices and micro-/nanomotors

Wave Interaction With Epsilon-znd-Mu-Near-Zero (emnz) Platforms and Nonreciprocal Metastructures

The concept of metamaterials has offered platforms for unconventional tailoring and manipulation of the light-matter interaction. In this dissertation, we explore several concepts and designs within this scope. We investigate some of the electromagnetic characteristics of the concept of “static optics”, i.e., wave interaction with structures in which both the relative effective permittivity and permeability attain near-zero values at a given operating frequency and thus the spatial distributions of the electric and magnetic fields exhibit curl-free features, while the fields are temporally dynamic. Using such structures, one might in principle ‘open up’ and ‘stretch’ the space, and have regions behaving electromagnetically as ‘single points’ despite being electrically large. We study some of the wave-matter interaction in these platforms and suggest possible designs for implementation of such structures in different frequency regimes and experimentally verify our findings in the microwave regime. Another research direction that is explored in this dissertation is the development of some nonreciprocal metaplatforms. We investigate theoretically an approach through which one-way electromagnetic wave flow can be achieved using properly designed nonlinearity combined with structural asymmetry. The approach is rather general and applicable for any desired frequency regime and opens doors for high performance “electromagnetic diodes” and nonreciprocal metasurfaces and metastructures. We also theoretically study the usage of time-dependent materials in achieving wave flow isolation within plasmonic waveguides environments. We also provide physical remarks on our various findings

The 2020 magnetism roadmap

Following the success and relevance of the 2014 and 2017 Magnetism Roadmap articles, this 2020 Magnetism Roadmap edition takes yet another timely look at newly relevant and highly active areas in magnetism research. The overall layout of this article is unchanged, given that it has proved the most appropriate way to convey the most relevant aspects of today's magnetism research in a wide variety of sub-fields to a broad readership. A different group of experts has again been selected for this article, representing both the breadth of new research areas, and the desire to incorporate different voices and viewpoints. The latter is especially relevant for thistype of article, in which one's field of expertise has to be accommodated on two printed pages only, so that personal selection preferences are naturally rather more visible than in other types of articles. Most importantly, the very relevant advances in the field of magnetism research in recent years make the publication of yet another Magnetism Roadmap a very sensible and timely endeavour, allowing its authors and readers to take another broad-based, but concise look at the most significant developments in magnetism, their precise status, their challenges, and their anticipated future developments. While many of the contributions in this 2020 Magnetism Roadmap edition have significant associations with different aspects of magnetism, the general layout can nonetheless be classified in terms of three main themes: (i) phenomena, (ii) materials and characterization, and (iii) applications and devices. While these categories are unsurprisingly rather similar to the 2017 Roadmap, the order is different, in that the 2020 Roadmap considers phenomena first, even if their occurrences are naturally very difficult to separate from the materials exhibiting such phenomena. Nonetheless, the specifically selected topics seemed to be best displayed in the order presented here, in particular, because many of the phenomena or geometries discussed in (i) can be found or designed into a large variety of materials, so that the progression of the article embarks from more general concepts to more specific classes of materials in the selected order. Given that applications and devices are based on both phenomena and materials, it seemed most appropriate to close the article with the application and devices section (iii) once again. The 2020 Magnetism Roadmap article contains 14 sections, all of which were written by individual authors and experts, specifically addressing a subject in terms of its status, advances, challenges and perspectives in just two pages. Evidently, this two-page format limits the depth to which each subject can be described. Nonetheless, the most relevant and key aspects of each field are touched upon, which enables the Roadmap as whole to give its readership an initial overview of and outlook into a wide variety of topics and fields in a fairly condensed format. Correspondingly, the Roadmap pursues the goal of giving each reader a brief reference frame of relevant and current topics in modern applied magnetism research, even if not all sub-fields can be represented here. The first block of this 2020 Magnetism Roadmap, which is focussed on (i) phenomena, contains five contributions, which address the areas of interfacial Dzyaloshinskii-Moriya interactions, and two-dimensional and curvilinear magnetism, as well as spin-orbit torque phenomena and all optical magnetization reversal. All of these contributions describe cutting edge aspects of rather fundamental physical processes and properties, associated with new and improved magnetic materials' properties, together with potential developments in terms of future devices and technology. As such, they form part of a widening magnetism 'phenomena reservoir' for utilization in applied magnetism and related device technology. The final block (iii) of this article focuses on such applications and device-related fields in four contributions relating to currently active areas of research, which are of course utilizing magnetic phenomena to enable specific functions. These contributions highlight the role of magnetism or spintronics in the field of neuromorphic and reservoir computing, terahertz technology, and domain wall-based logic. One aspect common to all of these application-related contributions is that they are not yet being utilized in commercially available technology; it is currently still an open question, whether or not such technological applications will be magnetism-based at all in the future, or if other types of materials and phenomena will yet outperform magnetism. This last point is actually a very good indication of the vibrancy of applied magnetism research today, given that it demonstrates that magnetism research is able to venture into novel application fields, based upon its portfolio of phenomena, effects and materials. This materials portfolio in particular defines the central block (ii) of this article, with its five contributions interconnecting phenomena with devices, for which materials and the characterization of their properties is the decisive discriminator between purely academically interesting aspects and the true viability of real-life devices, because only available materials and their associated fabrication and characterization methods permit reliable technological implementation. These five contributions specifically address magnetic films and multiferroic heterostructures for the purpose of spin electronic utilization, multi-scale materials modelling, and magnetic materials design based upon machine-learning, as well as materials characterization via polarized neutron measurements. As such, these contributions illustrate the balanced relevance of research into experimental and modelling magnetic materials, as well the importance of sophisticated characterization methods that allow for an ever-more refined understanding of materials. As a combined and integrated article, this 2020 Magnetism Roadmap is intended to be a reference point for current, novel and emerging research directions in modern magnetism, just as its 2014 and 2017 predecessors have been in previous years

ICR ANNUAL REPORT 2020 (Volume 27)[All Pages]

This Annual Report covers from 1 January to 31 December 202

Electrical control of magnetism by electric field and current-induced torques

While early magnetic memory designs relied on magnetization switching by locally generated magnetic fields, key insights in condensed matter physics later suggested the possibility to do it electrically. In the 1990s, Slonczewzki and Berger formulated the concept of current-induced spin torques in magnetic multilayers through which a spin-polarized current may switch the magnetization of a ferromagnet. This discovery drove the development of spin-transfer-torque magnetic random-access memories (STT-MRAMs). More recent research unveiled spin-orbit-torques (SOTs) and will lead to a new generation of devices including SOT-MRAMs. Parallel to these advances, multiferroics and their magnetoelectric coupling experienced a renaissance, leading to novel device concepts for information and communication technology such as the MESO transistor. The story of the electrical control of magnetization is that of a dance between fundamental research (in spintronics, condensed matter physics, and materials science) and technology (MRAMs, MESO, microwave emitters, spin-diodes, skyrmion-based devices, components for neuromorphics, etc). This pas de deux led to major breakthroughs over the last decades (pure spin currents, magnetic skyrmions, spin-charge interconversion, etc). As a result, this field has propelled MRAMs into consumer electronics products but also fueled discoveries in adjacent research areas such as ferroelectrics or magnonics. Here, we cover recent advances in the control of magnetism by electric fields and by current-induced torques. We first review fundamental concepts in these two directions, then discuss their combination, and finally present various families of devices harnessing the electrical control of magnetic properties for various application fields. We conclude by giving perspectives in terms of both emerging fundamental physics concepts and new directions in materials science.Comment: Final version accepted for publication in Reviews of Modern Physic