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Abstract Stretchable displays that combine light-emitting capabilities with mechanical compliance are essential building blocks of next-generation wearable electronics. However, their widespread applications are currently limited by complex device architecture, limited pixel density, and immature fabrication processes. In this study, we present the device design and material developments of intrinsically stretchable light-emitting drawing displays that can show arbitrary hand-drawing features. The alternating-current electroluminescent display uses a simplified architecture comprising coplanar interdigitated liquid metal electrodes, an electroluminescent layer, and a dielectric encapsulation layer. Ink patterns on the device are coupled with the interdigitated electrodes under alternating voltage stimulations, generating localized electric fields for bright emissions. Various inks are prepared for painting, stamping, and stencil printing. Arbitrary luminous features on the devices can be either long-lasting or transient in characteristics. These skin-like devices are made entirely of compliant materials that can withstand bending, twisting, and stretching manipulations. Due to the excellent mechanical deformability, the drawing displays can be conformally laminated on the skin as body-integrated optoelectronic communication devices for graphic information.

Abstract The last 20 years have witnessed growing impacts of the topological concept on the branches of physics, including materials, electronics, photonics, and acoustics. Topology describes objects with some global invariant property under continuous deformation, which in mathematics could date back to the 17th century and mature in the 20th century. In physics, it successfully underpinned the physics of the Quantum Hall effect in 1984. To date, topology has been extensively applied to describe topological phases in acoustic metamaterials. As artificial structures, acoustic metamaterials could be well theoretically analyzed, on‐demand designed, and easily fabricated by modern techniques, such as three‐dimensional printing. Some new theoretical topological models were first discovered in acoustic metamaterials analogous to electronic counterparts, associated with novel effects for acoustics closer to applications. In this review, we focused on the concept of topology and its realization in airborne acoustic crystals, solid elastic phononic crystals, and surface acoustic wave systems. We also introduced emerging concepts of non‐Hermitian, higher‐order, and Floquet topological insulators in acoustics. It has been shown that the topology theory has such a powerful generality that among the disciplines from electron to photon and phonon, from electronic to photonics and acoustics, from acoustic topological theory to acoustic devices, could interact and be analogous to fertilize fantastic new ideas and prototype devices, which might find applications in acoustic engineering and noise‐vibration control engineering in the near future.

Here the authors provide experimental evidence of extended topological valley-locked states. By splicing together Dirac semimetals and topological insulators, they demonstrate reduced backscattering and enhanced matching of SAW with interdigital transducers proposing this system for topological acoustics devices.

Weyl semimetals have interesting band-structure features that lead to unique properties. Here, the authors observe and study high-harmonic generation in type-II Weyl semimetal β-WP2 crystals.

The past decades have witnessed the flourishing of non-Hermitian physics in non-conservative systems, leading to unprecedented phenomena of unidirectional invisibility, enhanced sensitivity and more recently the novel topological features such as bulk Fermi arcs. Among them, growing efforts have been invested to an intriguing phenomenon, known as the non-Hermitian skin effect (NHSE). Here, we review the recent progress in this emerging field. By starting from the one-dimensional (1D) case, the fundamental concepts of NHSE, its minimal model, the physical meanings and consequences are elaborated in details. In particular, we discuss the NHSE enriched by lattice symmetries, which gives rise to unique non-Hermitian topological properties with revised bulk-boundary correspondence (BBC) and new definitions of topological invariants. Then we extend the discussions to two and higher dimensions, where dimensional surprises enable even more versatile NH.SE phenomena. Extensions of NHSE assisted with extra degrees of freedom such as long-range coupling, pseudospins, magnetism, non-linearity and crystal defects are also reviewed. This is followed by the contemporary experimental progress for NHSE. Finally, we provide the outlooks to possible future directions and developments.

Though non-Hermitian physics has contributed toward the advance of research in quantum, electronic and classical systems, previous work focused on zero- or one-dimensional systems. Here, the authors report higher-order non-Hermitian skin effects in a 2D acoustic higher-order topological insulator.

Abstract Higher-order topological insulators, as newly found non-trivial materials and structures, possess topological phases beyond the conventional bulk-boundary correspondence. In previous studies, in-gap boundary states such as the corner states were regarded as conclusive evidence for the emergence of higher-order topological insulators. Here, we present an experimental observation of a photonic higher-order topological insulator with corner states embedded into the bulk spectrum, denoted as the higher-order topological bound states in the continuum. Especially, we propose and experimentally demonstrate a new way to identify topological corner states by exciting them separately from the bulk states with photonic quantum superposition states. Our results extend the topological bound states in the continuum into higher-order cases, providing an unprecedented mechanism to achieve robust and localized states in a bulk spectrum. More importantly, our experiments exhibit the advantage of using the time evolution of quantum superposition states to identify topological corner modes, which may shed light on future exploration between quantum dynamics and higher-order topological photonics.

Wood is a sustainable material with big sound absorption potential based on its natural porous characteristics. However, the acoustic absorption performance of wood is greatly limited by the low permeability of wood structures. In this study, we prepared a new type of cellulose wood (CW) using a two-step delignification process on a natural basswood matrix followed by supercritical CO2 drying. The as-prepared CW exhibited a high air permeability of 33.78 Darcys (increase of 496.82%) and superior porous characteristics compared to the natural basswood, resulting in a significant improvement in the acoustic absorption performance with an increased average absorption of 106.25% and maximum absorption of 126.32%. The dissipation of sound energy in the structure of CW is well predicted by a designed porous media model. Moreover, a high specific stiffness of 2.14 × 105 m2 s−2 and a diffuse reflectance of 97.02% across the visible light were demonstrated for the CW as well. Such a fascinating multifunctional wood-derived material may provide new insights into the development of efficient and sustainable acoustic absorbers for various applications.

Thermal manipulation has garnered considerable attention for its potential applications in diverse areas, including microelectronics, thermal logic devices, and thermoelectrics [...]

Multistable mechanical metamaterials are a type of mechanical metamaterials with special features, such as reusability, energy storage and absorption capabilities, rapid deformation, and amplified output forces. These metamaterials are usually realized by series and/or parallel of bistable units. They can exhibit multiple stable configurations under external loads and can be switched reversely among each other, thereby realizing the reusability of mechanical metamaterials and offering broad engineering applications. This paper reviews the latest research progress in the design strategy, manufacture and application of multistable mechanical metamaterials. We divide bistable structures into three categories based on their basic element types and provide the criterion of their bistability. Various manufacturing techniques to fabricate these multistable mechanical metamaterials are introduced, including mold casting, cutting, folding and three-dimensional/4D printing. Furthermore, the prospects of multistable mechanical metamaterials for applications in soft driving, mechanical computing, energy absorption and wave controlling are discussed. Finally, this paper highlights possible challenges and opportunities for future investigations. The review aims to provide insights into the research and development of multistable mechanical metamaterials.

The quantum Hall effect (QHE) associated with Chern insulators reveals the non-trivial topological properties of two-dimensional electronic systems subject to strong magnetic field, which features finite Chern number C and chiral edge states. The latter promise robust electron transport and have received tremendous attention in both the condensed matter physics and classical systems including photonics and acoustics. In acoustics, circulating air flow has been introduced to create an effective gauge magnetic field, which breaks the time-reversal symmetry and leads to chiral edge states for acoustic waves. While the robust edge states may offer possible routes towards acoustic devices yielding unidirectional sound propagation, e.g., acoustic diodes, the mode density at the interfaces is limited by small Chern numbers of ±1. Here, we realize acoustic Chern insulators with large Chern numbers, i.e., |C|≥ 1 (|C| = 1, 2, 3, 4). The system is based on circulating air flow in a sonic crystal (SC) with fourfold rotational symmetry. The large Chern numbers are obtained by breaking multiple accidental degeneracies at (non-)high-symmetric points. Based on these Chern insulators, acoustic diodes are realized by joining structures of different Chern numbers. Up to eight propagation modes are supported on the interfaces, greatly improving the mode density and hence the propagation efficiency. Our design offers possible routes towards high-efficient and topologically robust acoustic diodes, which may further inspire acoustic non-reciprocal devices based on topological Chern insulators. Experimentally, our proposals can be realized based on angular-momentum-biased resonator arrays.

The quantum spin Hall effect is limited to one-dimensional lower boundary states which limits the possibilities for its exploitation in photonic devices. Here, the authors demonstrate a higher-order quantum spin Hall effect in a photonic crystal and observe opposite pseudospin corner states.

An acoustic analogue of a three-dimensional topological insulator (TI) has not been achieved, despite various realizations in other kinds of TIs. Here, the authors report a three-dimensional multi-order TI in an acoustic bilayer chiral structure, with robust surface or hinge sound transport.

Abstract Background Microtubule organization is essential for bipolar spindle assembly and chromosome segregation, which contribute to genome stability. Kinesin-5 Eg5 is known to be a crucial regulator in centrosome separation and spindle assembly in mammalian somatic cells, however, the functions and mechanisms of Eg5 in male meiotic cell division remain largely unknown. Results In this study, we have found that Eg5 proteins are expressed in mouse spermatogonia, spermatocytes and spermatids. After Eg5 inhibition by specific inhibitors Monastrol, STLC and Dimethylenastron, the meiotic spindles of dividing spermatocytes show spindle collapse and the defects in bipolar spindle formation. We demonstrate that Eg5 regulates spindle bipolarity and the maintenance of meiotic spindles in meiosis. Eg5 inhibition leads to monopolar spindles, spindle abnormalities and chromosome misalignment in cultured GC-2 spd cells. Furthermore, Eg5 inhibition results in the decrease of the spermatids and the abnormalities in mature sperms. Conclusions Our results have revealed an important role of kinesin-5 Eg5 in male meiosis and the maintenance of male fertility. We demonstrate that Eg5 is crucial for bipolar spindle assembly and chromosome alignment in dividing spermatocytes. Our data provide insights into the functions of Eg5 in meiotic spindle assembly of dividing spermatocytes.

Higher-order topological phenomenologies are usually observed separately, with each system giving rise to a specific type of topological insulator. Here, the authors realise a nonsymmorphic acoustic metacrystal where the first and the second band gap host dipole and quadrupole topology respectively.

Here, the authors report the experimental discovery of such a dimensional hierarchy of the topologically-protected 2D surface states, 1D hinge states and 0D corner states in a single 3D acoustic system by using higher-order topological sonic crystals.

Photonic higher-order topological insulators (HOTIs) based on kagome photonic crystals (PCs) possess rich physics of corner states for the unignorable long-range interactions. Theoretically, there should be multiple corner states, i.e., type I, antisymmetric type II, and symmetric type II corner states, in the kagome PCs. However, for the generation of some corner states, especially the symmetric type II corner states, it is necessary to obtain a large ratio of intercell coupling to intracell coupling, which makes the spacing between dielectric units very small and difficult to achieve experimentally. Here, we propose a scheme for the deterministic generation of multiple topological corner states based on an extremely expanded coupling condition. We construct an equilateral triangular cavity that consists of nontrivial unit cells in triangular PCs. All three topological corner states can exist robustly in the triangular cavity with large dielectric unit spacing. By establishing a tight-binding model for the nontrivial unit cell, we reveal that the extremely expanded coupling condition is the core physical mechanism for the deterministic generation of multiple corner states. The study provides a simple and deterministic method to generate multiple topological corner states, which has great potential in topological robust cavity, optical switches and lasers in integrated photonics on a silicon-on-insulator (SOI) or III-V active semiconductor platform.

Valley states can be used to realise topologically protected transport. Here, He et al. show that considering additional degrees of freedom, together with glide symmetry, allow the design of 2D acoustic topological pseudospin-valley coupled saddle surface states in 3D structures.

Topological phases of matter with robust edge states have revolutionized the fundamental intuitions for wave control. The recent development of higher-order topological insulators (HOTIs) realizes even lower dimensional topological states that enable versatile wave manipulations (e.g., light imaging). However, in conventional HOTIs, the topological states are usually protected by certain crystalline symmetries and therefore bounded at specific locations, hindering their applications in modern digital ears, which often prefer tunability and reconfigurability. Here, we report the reconfigurable light imaging based on topological corner states and anti-chiral edge states in a two-dimensional (2D) photonic HOTI with a honeycomb lattice of yttrium iron garnet (YIG, a ferrite material) rods. Sublattices A and B are applied with magnetic fields in opposite directions, which realize the so-called modified Haldane model that hosts anti-chiral edge modes. By further breaking the lattice’s inversion symmetry via adjusting the radii of A and B rods, topological edge states with valley degrees of freedom emerge, which not only exhibit valley-dependence but also surprisingly show anti-chiral behaviors. In the valley edge gap, which is of nontrivial higher-order topology, corner states appear. With different combinations of corner states and anti-chiral edge states, versatile reconfigurable light imaging can be realized. As examples, a multiplexing waveguide-resonator device, a pine tree imaging that can be lit up or put out at will and selective imaging for partial objects in a two-heart pattern are demonstrated. The proposed HOTI shows high potential in future intelligent devices with exciting tunable and reconfigurable functions, which may inspire a wide range of applications such as topological switching, imaging processing, and nonreciprocal integrated photonics.

Precise control of elastic waves is of great use in current technologies. Here, Yu et al. realize the analogue of quantum spin Hall effects for the elastic waves in a plain plate consisting of identical perforated holes in wavelength scales.

Abstract Thermoelectric multilayer thin films used in nanoscale energy conversion have been receiving increasing attention in both academic research and industrial applications. Thermal transport across multilayer interface plays a key role in improving thermoelectric conversion efficiency. In this study, the cross-plane thermal conductivities of nano-constructed Sb2Te3/(Cu, Ag, Au, Pt) thermoelectric multilayer thin films have been measured using time-domain thermoreflectance method. The interface morphology features of multilayer thin film samples were characterized by using scanning and transmission electron microscopes. The effects of interface microstructure on the cross-plane thermal conductivities of the multilayer thin films have been extensively examined and the thermal transfer mechanism has been explored. The results indicated that electron–phonon coupling occurred at the semiconductor/metal interface that strongly affected the cross-plane thermal conductivity. By appropriately optimizing the period thickness of the metal layer, the cross-plane thermal conductivity can be effectively reduced, thereby improving the thermoelectric conversion efficiency. This work presents both experimental and theoretical understanding of the thermal transport properties of Sb2Te3/metal multilayer thin film junctions with important implications for exploring a novel approach to improving the thermoelectric conversion efficiency.

Abstract All-angle negative refraction (AANR) of phononic crystals and its frequency range are dependent on mechanical properties of constituent materials and their spatial distribution. So far, it is impossible to achieve the maximum operation frequency range of AANR theoretically. In this paper, we will present a numerical approach for designing a two-dimensional phononic crystal with broadband AANR without negative index. Through analyzing the mechanism of AANR, a topology optimization problem aiming at broadband AANR is established and solved by bi-directional evolutionary structural optimization method. The optimal steel/air phononic crystal exhibits a record AANR range over 20% and its refractive properties and focusing effects are further investigated. The results demonstrate the multifunctionality of a flat phononic slab including superlensing effect near upper AANR frequencies and self-collimation at lower AANR frequencies.

Thermal conductivity: in a loop The thermal conductivity across stacked MoTe2 layers exhibits a hysteresis loop, as the temperature changes. Similar effects in other materials have been exploited for the implementation of thermal memories for the storage of phononic information. Now, a team from Nanjing University in China studies the thermal properties along the perpendicular axis of stacked layers of MoTe2, a 2D material that undergoes a well-known structural phase transition around 250 K. The authors report an abrupt jump in the thermal conductivity around that temperature. The conductivity measured at 255 K during warming is about 10% higher than upon cooling, a hysteretic behavior dominated by phonons. With a performance comparable to other phase-change materials, MoTe2 is a very promising candidate for the implementation of all-phononic thermal memories, working at 255 K with the thermal information being “written/erased” by adjusting the temperature.

We synthesized the copper foam sustained silica aerogel (CFSA) by sol-gel transition followed by CO2 supercritical drying. The as-prepared CFSA exhibits excellent sound absorption capability and favorable compressive properties. Incorporation of epoxy resin during sol-gel process can improve the combination between silica aerogel and copper foam framework, which helps to significantly increase the average sound absorption from ∼36% to ∼55% (200-3900 Hz) and the maximum sound absorption coefficient from 0.78 to 0.99. A high Young’s modulus of ∼11.01 MPa and compression strength of ∼0.30 MPa were demonstrated for CFSA as well. The fabricated CFSA also shows some advantages, e.g., lightweight (density of 0.28 g/cm3) and hydrophobic. Such fascinating artificial composite may provide new insights into the development of strong and effective aerogel sound-absorbing materials for various applications.

Bloch oscillations are a fundamental electron transport phenomenon in condensed matter. Here, the authors experimentally realize spatial Bloch oscillations in a non-Hermitian integrated photonic system using CMOS compatible fabrication processes, contributing to improving the understanding of non-Hermitian transport phenomena.

Monolayer antimony (antimonene) has been reported for its excellent properties, such as tuneable band gap, stability in the air, and high mobility. However, growing high quality, especially large-area antimonene, remains challenging. In this study, we report the direct growth of antimonene on c-plane sapphire substrate while using molecular beam epitaxy (MBE). We explore the effect of growth temperature on antimonene formation and present a growth phase diagram of antimony. The effect of antimony sources (Sb2 or Sb4) and a competing mechanism between the two-dimensional (2D) and three-dimensional (3D) growth processes and the effects of adsorption and cracking of the source molecules are also discussed. This work offers a new method for growing antimonene and it provides ideas for promoting van der Waals epitaxy.

Pepper (Capsicum annuum L.) is sensitive to heat stress (HS). Heat shock proteins 70 (Hsp70s) play a crucial role in protecting plant cells against HS and control varies characters in different plants. However, CaHsp70-1 gene was not well characterized in pepper. In this study, CaHsp70-1 was cloned from the pepper thermotolerant line R9, which encoded a protein of 652 amino acids, with a molecular weight of 71.54 kDa and an isoelectric point of 5.20. CaHsp70-1 belongs to the cytosolic Hsp70 subgroup, and best matched with tomato SlHsp70. CaHsp70-1 was highly induced in root, stem, leaf and flower in R9 with HS treatment (40 °C for 2 h). In both thermosensitive line B6 and thermotolerant line R9, CaHsp70-1 significantly increased after 0.5 h of HS (40 °C), and maintained in a higher level after 4 h HS. The expression of CaHsp70-1 induced by CaCl2, H2O2 and putrescine (Put) under HS were difference between B6 and R9 lines. The different expression patterns may be related to the differences in promoters of CaHsp70-1 from the two lines. These results suggest that CaHsp70-1 as a member of cytosolic Hsp70 subgroup, may be involved in HS defense response via a signal transduction pathway contained Ca2+, H2O2 and Put.

A silicon waveguide consisting of passive parity-time (PT) symmetry optical potentials connected with a distributed Bragg reflector (DBR)-based resonator is proposed to achieve nonreciprocal waveguide transmission. The unidirectional reflectionless waveguide implementing PT symmetry is discussed by consistent coupling mode theory and finite-difference time-domain (FDTD) simulation results. Due to the high field confinement in the DBR cavity, transmission of a light pulse through the device is analyzed in the nonlinear optical regime using FDTD simulations. The combination of the nonlinear DBR cavity and the passive PT symmetric grating results in unidirectional transmission in the silicon waveguide, while still keeping the reflection minimum in the desired direction. The numerical simulation shows an extinction ratio of about 20 dB at the telecom wavelength of around 1550 nm.

Time-reversal symmetry (TRS) of electrons is associated with an anti-unitary operator with T 2 = − 1 , which induces Kramers degeneracy and plays an important role in realizing the quantum spin Hall effect (QSHE). By contrast, TRS of photons is described by T b 2 = 1 . We point out that due to this difference, TRS is not the necessary condition for the construction of the photonic analogue of the QSHE. Instead, by constructing an artificial pseudo TRS T p with T p 2 = − 1 in a photonic system, one can realize the photonic Kramers degeneracy and a pair of topological protected edge states, a photonic analogue of the QSHE. Specifically, by retrieving the optical parameters of materials with the pseudo TRS, we propose a photonic topological insulator (PTI) utilizing a pair of double-degenerate transverse electric (TE) and transverse magnetic (TM) polarizations to mimic the spin up and down states of the electron. We demonstrate that the unidirectional polarization-dependent transportation of TE and TM edge states can be realized in this system based on computer simulations. For all possible symmetry types, we check the robustness of these topological states by using a complete set of impurities, including three Pauli matrices and one complex conjugate operator. The results show that the PTI is protected by the pseudo TRS T p . In general, an arbitrary pair of optical polarizations on the Bloch sphere can be utilized to construct photonic pseudospin states and the PTI. Our findings confirm the physical meaning of the pseudo TRS and may provide guidance for future PTI designs.

The original version of this Article contained errors in the second sentence in the legend of Fig. 1, which incorrectly read ‘These two elastic insulators are identical in lattice constant a (3a 0), plate thickness (0.4a 0), and radius of perforated holes r (0.18a 0) but different hole-center distance characterized by b.’ The correct version states ‘plate thickness (√3 × 0.4a 0)’ in place of ‘plate thickness (0.4a 0)’ and ‘radius of perforated holes r (√3 × 0.18a 0)’ rather than ‘radius of perforated holes r (0.18a 0)’.The first sentence of the ‘Sample preparation’ section of the Methods originally incorrectly read ‘Our samples are prepared exclusively on polished stainless-steel plates (Type 201, mass density 7803 kg m−3) with a fixed plate thickness 7.82 mm.’ In the corrected version, ‘mass density 7903 kg m−3’ replaces ‘mass density 7803 kg m−3’.The second sentence in the legend of Supplementary Fig. 3, originally incorrectly read ‘The symmetry of the phononic crystal remains unchanged as C6ν, and thickness of the substrates H (equals to 0.4a 0), lattice constant a (equals to 3a 0) and radius of perforated holes r (equals to 0.18 a 0) maintain constant.’ The correct version states ‘√3 × 0.4a 0’ in place of ‘0.4a 0’ and ‘√3 × 0.18a 0’ rather than ‘0.18a 0’.This has been corrected in both the PDF and HTML versions of the Article.

We present a design for a two-dimensional omnidirectional acoustic absorber that can achieve 98.6% absorption of acoustic waves in water, forming an effective acoustic black hole. This artificial black hole consists of an absorptive core coated with layers of periodically distributed polymer cylinders embedded in water. Effective medium theory describes the response of the coating layers to the acoustic waves. The polymer parameters can be adjusted, allowing practical fabrication of the absorber. Since the proposed structure does not rely on resonances, it is applicable to broad bandwidths. The design might be extended to a variety of applications.

Recent explorations of topology in physical systems have led to a new paradigm of condensed matters characterized by topologically protected states and phase transition, for example, topologically protected photonic crystals enabled by magneto-optical effects. However, in other wave systems such as acoustics, topological states cannot be simply reproduced due to the absence of similar magnetics-related sound–matter interactions in naturally available materials. Here, we propose an acoustic topological structure by creating an effective gauge magnetic field for sound using circularly flowing air in the designed acoustic ring resonators. The created gauge magnetic field breaks the time-reversal symmetry, and therefore topological properties can be designed to be nontrivial with non-zero Chern numbers and thus to enable a topological sonic crystal, in which the topologically protected acoustic edge-state transport is observed, featuring robust one-way propagation characteristics against a variety of topological defects and impurities. Our results open a new venue to non-magnetic topological structures and promise a unique approach to effective manipulation of acoustic interfacial transport at will.

We design a structure to realize Rabi splitting and Rabi oscillation in acoustics. We develop rigorous analytical models to analyze the splitting effect from the aspect of phase matching, and from the aspect of mode coupling using a coupled mode model. In this model, we discover that the splitting effect is caused by the coupling of the Fabry–Perot fundamental mode with the resonant mode of an artificial acoustic ‘atom’. We then extract the coupling strength and analyze the impact of structural parameters on it. In addition, we demonstrate Rabi oscillation in the time domain. Such quantum phenomena in the classical regime may have potential applications in the design of novel ultrasonic devices.