114 research outputs found
Space-Time Phononic Crystals with Anomalous Topological Edge States
It is well known that an interface created by two topologically distinct
structures could host nontrivial edge states that are immune to defects. In
this letter, we introduce a one-dimensional space-time phononic crystal and
study the associated anomalous topological edge states. A space-decoupled time
modulation is assumed. While preserving the key topological feature of the
system, such a modulation also duplicates the edge state mode across the
spectrum, both inside and outside the band gap. It is shown that, in contrast
to conventional topological edge states which are excited by frequencies in the
Bragg regime, the time-modulation-induced frequency conversion can be leveraged
to access topological edge states at a deep subwavelength scale where the
entire phononic crystal size is merely 1/5.1 of the wavelength. This remarkable
feature could open a new route for designing miniature devices that are based
on topological physics
Engineering Moir\'e Meta-crystals with Conventional Photonic and Phononic Structures
Recent discoveries on Mott insulating and unconventional superconducting
states in twisted bilayer graphene with Moir\'e superlattices have reshaped the
landscape of ''twistronics'' and paved the way for developing high-temperature
superconductors and new devices for quantum computing and sensing. Meanwhile,
artificially structured photonic and phononic metamaterials/crystals (or
meta-crystals) have become a fertile playground for emulating
quantum-mechanical features of condensed matter systems, revealing new routes
for robust control of classical waves. Drawing inspiration from the success of
twisted bilayer graphene, this perspective casts an overarching framework of
the emerging Moir\'e photonic and phononic meta-crystals that promise novel
classical-wave devices. We begin with the fundamentals of Moir\'e
superlattices, before highlighting recent works that exploit twist angle and
interlayer coupling as new ingredients to engineer and tailor the band
structures and effective material properties of photonic and phononic
meta-crystals. We finally discuss future directions and promises of this
emerging area in materials science and wave physics.Comment: 4 figure
Phononic Crystal Made of Multilayered Ridges on a Substrate for Rayleigh Waves Manipulation
International audienceWe present a phononic crystal to achieve efficient manipulation of surface acoustic waves (SAW). The structure is made of finite phononic micro-ridges arranged periodically in a substrate surface. Each ridge is constructed by staking silicon and tungsten layers so that it behaves as one-dimensional phononic crystal which exhibits band gaps for elastic waves. The band gap allows the existence of resonance modes where the elastic energy is either confined within units in the free end of the ridge or the ones in contact with the substrate. We show that SAW interaction with localized modes in the free surface of the ridge gives rise to sharp attenuation in the SAW transmission while the modes confined within the ridge/ substrate interface cause broad band attenuations of SAW. Furthermore, we demonstrate that the coupling between the two kinds of modes within the band gap gives high SAW transmission amplitude in the form of Fano like peaks with high quality factor. The structure could provide an interesting solution for accurate SAW control for sensing application for instance
Study of tantalum and iridium as adhesion layers for Pt/LGS high temperature SAW devices
International audienceIn this paper, we report on the use of tantalum and iridium as adhesion layers for platinum electrodes used in high temperature SAW devices based on langasite substrates (LGS). Unlike iridium, tantalum exhibits a great adhesive strength, and a very low mobility through the Pt film, ensuring a device lifetime of at least half an hour at 1000°C. The latter is limited by morphological modifications of platinum, starting by the apparition of crystallites on the surface, and followed by important terracing and breaking of the film continuity. SNMS and XRD measurements allowed us to show that these phenomena are likely intrinsic to platinum film, whatever be the nature of the adhesion layer. Finally, after having outlined a possible scenario leading to this deterioration, we consider some solutions that could replace platinum in order to increase the lifetime of LGS-based SAW devices in high temperatures conditions
- …