Fermi arc reconstruction in synthetic photonic lattice

The chiral surface states of Weyl semimetals have an open Fermi surface called Fermi arc. At the interface between two Weyl semimetals, these Fermi arcs are predicted to hybridize and alter their connectivity. In this letter, we numerically study a one-dimensional (1D) dielectric trilayer grating where the relative displacements between adjacent layers play the role of two synthetic momenta. The lattice emulates 3D crystals without time-reversal symmetry, including Weyl semimetal, nodal line semimetal, and Chern insulator. Besides showing the phase transition between Weyl semimetal and Chern insulator at telecom wavelength, this system allows us to observe the Fermi arc reconstruction between two Weyl semimetals, confirming the theoretical predictions.Comment: Main text: 4 pages, 4 figures. Supplemental materials: 19 pages, 18 figure

On the origin of the Kerker phenomena

We provide an insight into the origin of the phenomena reported 40 years ago by Kerker, Wang and Giles (Journal of the Optical Society of America, 73, 6, pp. 765-767, (1983)). We show that the impedance and refractive index matching conditions, discussed in Sections II and IV of the seminal paper, are intimately related with space-time symmetries. We derive our results starting from the theory of representations of the Poincar\'e group, as it is the theory on which one of the most elemental descriptions of electromagnetic waves is based. We show that fundamental features of electromagnetic waves in material environments can be derived from group theoretical arguments. In particular, we identify the Casimir invariants of $P_{\scriptscriptstyle{{3,1}}}$ subgroup as the magnitudes which describe the nature of monochromatic electromagnetic waves propagating in matter. Finally, we show that the emergence of the Kerker phenomena is associated with the conservation of such Casimir invariants in piecewise homogeneous media

Transversality-Enforced Tight-Binding Model for 3D Photonic Crystals aided by Topological Quantum Chemistry

Tight-binding models can accurately predict the band structure and topology of crystalline systems and they have been heavily used in solid-state physics due to their versatility and low computational cost. It is quite straightforward to build an accurate tight-binding model of any crystalline system using the maximally localized Wannier functions of the crystal as a basis. In 1D and 2D photonic crystals, it is possible to express the wave equation as two decoupled scalar eigenproblems where finding a basis of maximally localized Wannier functions is feasible using standard Wannierization methods. Unfortunately, in 3D photonic crystals, the vectorial nature of the electromagnetic solutions cannot be avoided. This precludes the construction of a basis of maximally localized Wannier functions via usual techniques. In this work, we show how to overcome this problem by using topological quantum chemistry which will allow us to express the band structure of the photonic crystal as a difference of elementary band representations. This can be achieved by the introduction of a set of auxiliary modes, as recently proposed by Solja\v{c}i\'c et. al., which regularize the $\Gamma$-point obstruction arising from transversality constraint of the Maxwell equations. The decomposition into elementary band representations allows us to isolate a set of pseudo-orbitals that permit us to construct an accurate transversality-enforced tight-binding model (TETB) that matches the dispersion, symmetry content, and topology of the 3D photonic crystal under study. Moreover, we show how to introduce the effects of a gyrotropic bias in the framework, modeled via non-minimal coupling to a static magnetic field. Our work provides the first systematic method to analytically model the photonic bands of the lowest transverse modes over the entire BZ via a TETB model.Comment: 3 figure

Carbamazepine-induced thrombocytopenic purpura in a child: Insights from a genomic analysis

To the Editor, Carbamazepine is an effective anticonvulsant and has a relatively low incidence of adverse effects, although it occasionally causes hema- tologic disorders. We herein describe a patient with carbamazepine- induced thrombocytopenic purpura that was investigated by pharma- cological, immunological and genomic assays

Short-Term Outcomes of an ESDM Intervention in Italian Children with Autism Spectrum Disorder following the COVID-19 Lockdown

The COVID-19 pandemic caused a temporary lockdown period in Italy, during which the delivery of in-person treatment for children with autism spectrum disorder (ASD) in public health services was discontinued. This occurrence represented a crucial challenge for both families and professionals. We assessed the short-term outcomes of a sample of 18 children who received an early intervention with the Early Start Denver Model (ESDM), delivered at low intensity over one year in the pre-pandemic period, after six months of interruption of in-presence treatment due to lockdown restrictions. Children who received the ESDM treatment maintained their gains in sociocommunicative skills and did not exhibit any developmental regression. Additionally, there was evidence of a decrease in the restrictive and repetitive behavior (RRB) domain. The parents, who were already familiar with the principles of the ESDM, only received telehealth support from therapists that aimed to sustain the gains already achieved. We believe that it is always helpful to support parents in their daily lives by implementing interactional and play skills with their children to integrate and consolidate the results obtained in the individual interventions conducted by experienced therapists

3D Topological Photonic Crystals: Theoretical Methods and Applications

216 p.The concept of topology has revolutionized our understanding of condensed matter physics, leading to the discovery of novel electronic phases and the emergence of topological materials. In recent years, this concept has been extended to the field of photonics, where it has led to the design of a new class of materials known as topological photonic crystals. These materials possess nontrivial topological properties that can lead to unique and robust light propagation phenomena. This thesis presents a comprehensive study of 3D topological photonic crystals, with a focus on the discovery of novel topological phases and the development of new methods for their characterization and design. The main contributions of this work are the proposal and investigation of 3D topological photonic phases, which include: the 3D Chern photonic insulator; the axion photonic insulator; and the 3DWeyl semimetal with unpaired photonicWeyl points. These phases exhibit unique features, such as vectorial bulk-boundary correspondence, closed Fermi loops, chiral hinge channels, and forbidden surface Fermi arcs, which have not been proposed before in 3D photonic crystals. To approach topology in 3D electromagnetism, we propose dimension-specific characterization methods, including vectorial photonic Wilson loops and transversality-enforced tight-binding models. These methods allow us to overcome the theoretical challenges associated with the vectorial nature of light, and permit us to model and characterize the topological properties of 3D photonic systems in detail. Throughout this thesis, we also suggest possible implementations to realize these topological phases, which include PhC domain walls, gyrotropic structures, and quantum emitters coupled to PhCs. Our goal is to demonstrate their potential for applications in guided-light communication, optical switching, particle detection, magneto-photonics, and quantum simulations. Overall, this work aims to contribute to a deeper understanding of topological phenomena in 3D electromagnetism and proposes novel investigation methods and possible applications. We hope that the tools and designs developed in this thesis can be used as a starting point to realize these topological phases in real-world photonic devices

Resonant helicity mixing of electromagnetic waves propagating through matter

Dual scatterers preserve the helicity of an incident field, whereas antidual scatterers flip it completely. In this setting of linear electromagnetic scattering theory, we provide a completely general proof on the nonexistence of passive antidual scatterers. However, we show that scatterers fulfilling the refractive index matching condition flip the helicity of the fields very efficiently without being in contradiction with the law of energy conservation. Moreover, we find that this condition is paired with the impedance matching condition in several contexts of electromagnetism and, in particular, within Fresnel's and Mie's scattering problems. Finally, we show that index-matched media induce a resonant helicity mixing on the propagating electromagnetic waves. We reach this conclusion by identifying that the refractive index matching condition leads to the phenomenon of avoided crossing.J.L.A., J.O.T., C.D., and A.G.E. acknowledge support from Project No. PID2019-109905GA-C22 of the Spanish Ministerio de Ciencia, Innovación y Universidades (MICIU),IKUR Strategy under the collaboration agreement between Ikerbasque Foundation and DIPC on behalf of the Department of Education of the Basque Government, the Basque Government Elkartek program (KK-2021/00082), Programa de ayudas de apoyo a los agentes de la Red Vasca de Ciencia, Tecnología e Innovación acreditados en la categoría de Centros de Investigación Básica y de Excelencia (Programa BERC) from the Departamento de Universidades e Investigación del Gobierno Vasco and Centros Severo Ochoa AEI/CEX2018-000867-S from the Spanish Ministerio de Ciencia e Innovación. J.O.T. acknowledges support from the Juan de la Cierva Fellowship No. FJC2021-047090-I of MCIN/AEI/10.13039/501100011033 and NextGenerationEU/PRTR. G.M.T. received funding from the IKUR Strategy under the collaboration agreement between Ikerbasque Foundation and DIPC/MPC on behalf of the Department of Education of the Basque Government.With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2018-000867-S).Peer reviewe

Supporting Information. Resonant helicity mixing of photons in matter

We first provide the explicit expressions of Fresnel and Mie coefficients under the duality and resonant mixing conditions. Then, we also attach the calculus of the expected value of helicity maps in the large and small sphere regime. Finally, we include the technical details of the time-independent perturbation theory applied to the photon hamiltonian.Peer reviewe

Cubic 3D Chern photonic insulators with orientable large Chern vectors

Time Reversal Symmetry (TRS) broken topological phases provide gapless surface states protected by topology, regardless of additional internal symmetries, spin or valley degrees of freedom. Despite the numerous demonstrations of 2D topological phases, few examples of 3D topological systems with TRS breaking exist. In this article, we devise a general strategy to design 3D Chern insulating (3D CI) cubic photonic crystals in a weakly TRS broken environment with orientable and arbitrarily large Chern vectors. The designs display topologically protected chiral and unidirectional surface states with disjoint equifrequency loops. The resulting crystals present the following characteristics: First, by increasing the Chern number, multiple surface states channels can be supported. Second, the Chern vector can be oriented along any direction simply changing the magnetization axis, opening up larger 3D CI/3D CI interfacing possibilities as compared to 2D. Third, by lowering the TRS breaking requirements, the system is ideal for realistic photonic applications where the magnetic response is weak.A.G.E., C.D. and M.B.P. acknowledge support from the Spanish Ministerio de Ciencia e Innovación (PID2019-109905GA-C2) and from Eusko Jaurlaritza (IT1164-19, KK-2019/00101 and KK-2021/00082). M.G.D., I.R. and M.G.V. acknowledge the Spanish Ministerio de Ciencia e Innovacion (grant PID2019-109905GB-C21). J.L.A. acknowledges support from the Spanish Ministerio de Ciencia e Innovación (PID2019-109905GA-C2). The work of B.B. is supported by the Air Force Office of Scientific Research under award number FA9550-21-1-0131. C.D. acknowledges financial support from the MICIU through the FPI PhD Fellowship CEX2018-000867-S-19-1. The work of J.L.M. has been supported by Spanish Science Ministry grant PGC2018-094626-BC21 (MCIU/AEI/FEDER, EU) and Basque Government grant IT979-16. A.G.E. and M. G. V. acknowledge funding from Programa Red Guipuzcoana de Ciencia, Tecnología e Innovación 2021 (Grant Nr. 2021-CIEN-000070-01. Gipuzkoa Next).Peer reviewe