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Plants are vulnerable to heat stress, especially during reproductive development. The heat shock response (HSR) in the cytosol and nucleus, as well as the unfolded protein response (UPR) in the endoplasmic reticulum (ER), are two mechanisms that enable plants to survive heat stress. Excessive heat or ER stresses lead to cell death when the UPR cannot repair stress damage, but the means by which cell survival or death is determined remains unclear. In this study, we used a genome-wide association study (GWAS) to identify that a cluster of five Immune-associated nucleotide-binding protein (IAN) genes (IAN2 to IAN6) is responsible for variation in heat tolerance at the reproductive stage in Arabidopsis thaliana. These IAN genes have both unique and overlapping functions in the negative regulation of heat tolerance, and their loss of function singly or in combination confers increased heat tolerance, measured by a lower number of barren siliques and a higher seedling survival rate under heat. The loss of rice IAN1 gene function also leads to enhanced heat tolerance, suggesting a conserved function of plant IANs. Transcriptome analysis revealed enhanced expression of HSR and UPR genes, as well as reduced cell death, under heat and ER stress in the mutant of IAN6, a major effect member in Arabidopsis. Furthermore, the IAN proteins were found to promote cell death induced by heat stress, ER stress, and cell death-inducing molecules. Thus, the Arabidopsis IAN genes repress heat tolerance, probably through the HSR and UPR and by enhancing the cell death pathway. The IAN2 to IAN6 proteins are partially localized to the ER, suggesting a direct role in the UPR and UPR-mediated cell death. In addition, a natural IAN6 variant from more heat-tolerant Arabidopsis accessions confers greater heat tolerance and induces less cell death compared with the natural variant from less heat-tolerant accessions. The heat-tolerant IAN6 variant is associated with a higher maximum temperature of the warmest month at its collection sites compared with the heat-sensitive variant. Taken together, these results reveal an important role of Arabidopsis IAN2 to IAN6 genes in the regulation of the HSR, UPR, and cell death, and suggest that their natural variations have adaptive functions in heat tolerance.

(1-x)(Pb0.97La0.02)(Zr0.5Sn0.4Ti0.1)O3-x(Na0.5Bi0.5)0.94Ba0.06TiO3 (x = 0 ∼ 0.4) ceramics have been prepared and investigated. The ceramics consist of perovskite solid solution matrix and precipitated, isolated SnO2 particle, resulting in 0–3 type composite structure. With increasing x value, the room temperature crystal structure of perovskite solid solution transforms from tetragonal to pseudocubic, therefore, the electrical property evaluates form robust antiferroelectric at x = 0, metastable antiferroelectric at x = 0.1, and then relaxor ferroelectric at x > 0.1. Moreover, the breakdown strength is enhanced due to the composite structure and reaches maximum value of 190 kV/cm at x = 0.2. Both the phase transition and enhanced breakdown strength are helpful to improve energy storage property, the x = 0.2 ceramic shows largest recoverable energy density wrec of 1.84 J/cm3, discharge efficiency η of 86.6 %. Especially, both wrec and η illustrates significantly improved thermal stability within 25−125 °C.

Topological insulators (TIs) can host an insulating gapped bulk with conducting gapless boundary states in lower dimensions than the bulk. To date, various kinds of classical wave TIs with gapless symmetry-protected boundary states have been discovered, promising for the efficient confinement and robust guiding of waves. However, for airborne sound, an acoustic analogue of a three-dimensional TI has not been achieved due to its spinless nature. Here, we experimentally demonstrate a three-dimensional topological acoustic crystal with pseudospins using bilayer chiral structures, in which multi-order topological bandgaps are generated step by step via elaborately manipulating the corresponding spatial symmetries. We observe acoustic analogues of 1st-order (two-dimensional gapless surface Dirac cones) and 2nd-order (one-dimensional gapless hinge Dirac dispersion) TIs in three dimensions, supporting robust surface or hinge sound transport. Based solely on spatial symmetry, our work provides a route to engineer the hierarchies of TIs and explore topological devices for three-dimensional spinless systems., 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.

Understanding unidirectional and topological wave phenomena requires the unveiling of intrinsic geometry and symmetry for wave dynamics. This is essential yet challenging for the flexible control of near-field evanescent waves, highly desirable in broad practical scenarios ranging from information communication to energy radiation. However, exploitations of near-field waves are limited by a lack of fundamental understanding about inherent near-field symmetry and directional coupling at sub-wavelengths, especially for longitudinal waves. Here, based on the acoustic wave platform, we show the efficient selective couplings enabled by near-field symmetry properties. Based on the inherent symmetry properties of three geometrically orthogonal vectors in near-field acoustics, we successfully realize acoustic Janus, Huygens, spin sources and quadrupole hybrid sources, respectively. Moreover, we experimentally demonstrate fertile symmetry selective directionality of those evanescent modes, supported by two opposite meta-surfaces. The symmetry properties of the near-field acoustic spin angular momenta are revealed by directly measuring local vectorial fields. Our findings advance the understanding of symmetries in near-field physics, supply feasible approaches for directional couplings, and pave the way for promising acoustic devices in the future., It is essential yet challenging to achieve flexible control of near-field evanescent waves, highly desirable in broad practical scenarios. Here, we show the efficient symmetry selective couplings for near-field acoustics

Pyroelectric materials have a huge market in daily life applications and high pyroelectric performances near room temperature are highly desired. Here we report high pyroelectric performance with adjustable peak performance temperature of 29–46.2 °C in the (1 − x)Pb0.99Nb0.02[(Zr0.57Sn0.43)0.937Ti0.063]0.98O3–xZnO ((1 − x)PNZST–xZnO) composite. The x = 0.1 composite has a peak pyroelectric coefficient of 1053.9 × 10−4 C m−2 K−1 and figures of merit of Fv = 1249.4 × 10−2 m2 C−1, Fd = 876.3 × 10−5 Pa−1/2, and Fi = 832.7 × 10−10 m V−1 at around 39 °C. It is found that a robust room temperature ferroelectric state is realized in antiferroelectric PNZST due to ZnO-induced internal strain. The thermal-driven ferroelectric to antiferroelectric transition leads to high pyroelectric performance. This work provides a promising material candidate for high performance pyroelectric devices.

Symmetry and topology are two fundamental aspects of many quantum states of matter. Recently, new topological materials, higher-order topological insulators, were discovered, featuring, e.g., bulk-edge-corner correspondence that goes beyond the conventional topological paradigms. Here, we discover experimentally that the nonsymmorphic $p4g$ acoustic metacrystals host a symmetry-protected hierarchy of topological multipoles: the lowest band gap has a quantized Wannier dipole and can mimic the quantum spin Hall effect, while the second band gap exhibits quadrupole topology with anomalous Wannier bands. Such a topological hierarchy allows us to observe experimentally distinct, multiplexing topological phenomena and to reveal a topological transition triggered by the geometry-transition from the $p4g$ group to the $C_{4v}$ group which demonstrates elegantly the fundamental interplay between symmetry and topology. Our study demonstrates an instance that classical systems with controllable geometry can serve as powerful simulators for the discovery of novel topological states of matter and their phase transitions., Comment: 5 figures. Accepted by Nature Communications

Thermoelectric materials have been hotly explored for potential applications of environmentally friendly electrical generators and freon-free refrigerators. ZrTe5 and HfTe5 crystals have a superior...

In recent years, the layered semiconductor tin selenide (SnSe) has been of great interest in the thermoelectric field because of its remarkable thermoelectric potential. Here, the as-grown Sn0.98Se...

During cytokinesis, the organization of the spindle midzone and chromosome segregation is controlled by the central spindle, a microtubule cytoskeleton containing kinesin motors and non-motor microtubule-associated proteins. The anaphase spindle elongation 1/protein regulator of cytokinesis 1/microtubule associated protein 65 (Ase1/PRC1/MAP65) family of microtubule-bundling proteins are key regulators of central spindle assembly, mediating microtubule crosslinking and spindle elongation in the midzone. Ase1/PRC1/MAP65 serves as a complex regulatory platform for the recruitment of other midzone proteins at the spindle midzone. Herein, we summarize recent advances in understanding of the structural domains and molecular kinetics of the Ase1/PRC1/MAP65 family. We summarize the regulatory network involved in post-translational modifications of Ase1/PRC1 by cyclin-dependent kinase 1 (Cdk1), cell division cycle 14 (Cdc14) and Polo-like kinase 1 (Plk1) and also highlight multiple functions of Ase1/PRC1 in central spindle organization, spindle elongation and cytokinesis during cell division.

Degradation of SrTiO3-based grain boundary barrier layer ceramic was studied by applying a direct current voltage of 40 V for 12 days at room temperature. The degradation of the ceramic mainly showed as an asymmetrical resistivity degradation with the degradation of the reverse resistivity being greater than the forward resistivity. By using a scanning microwave impedance microscopy (SMIM), we observed an asymmetry in carrier concentration within the grain boundaries after the aging treatment. It was proposed that the asymmetrical migration of oxygen ions in O-rich region caused the asymmetrical degradation of resistivity. Direct current induced degradation reduces the effectiveness of ceramics capacitors and great efforts should be made to prevent this type of degradation.

Over the past few years, the rapid development in the fields of condensed matter physics, electronic, and photonic systems have inspired the design and experimental demonstration of various acoustic topological insulators (TIs). Among these, the topologically protected one-way propagation is a phenomenon that is gaining increased attention. Pseudospin states, which is the analogue of the quantum spin Hall effect from electronic systems, has been proven to enable topological edge states in acoustics. Similarly, the valley Hall (VH) effect is also observed in acoustic systems and provides a pair of valley vortex states with opposite chirality. These valley vortex states can similarly form topologically protected edge states and, in turn, realize robust one-way propagation. However, the differences in the physics behind these acoustic systems give rise to distinct features such as different angle selections and immunization levels to various types of defects. This article conducts a comparison study between topological states in valley Hall phononic crystals and TIs that reveals the differences and similarities in several aspects. Both of them have topologically protected edge states and thus the robust one-way propagation. For the maximum transmission incident angle and defect immunization, however, VH topological waveguides and TI waveguides show different characteristics.

How diversity in growth thermo-responsiveness is generated for local adaptation is a long-standing biological question. We investigated molecular genetic basis of natural variations in thermo-responsiveness of plant architecture in Arabidopsis thaliana. We measured the extent of rosette architecture at 22°C and 28°C in a set of 69 natural accessions and determined their thermo-responsiveness of plant architecture. A genome-wide association study was performed to identify major loci for variations in thermo-responsiveness. The SAUR26 subfamily, a new subfamily of SAUR genes, was identified as a major locus for the thermo-responsive architecture variations. The expression of SAUR26/27/28 is modulated by temperature and PIF4. Extensive natural polymorphisms in these genes affect their RNA expression levels and protein activities and influence the thermo-responsiveness of plant architecture. In addition, the SAUR26 subfamily genes exhibit a high variation frequency and their variations are associated with the local temperature climate. This study reveals that the SAUR26 subfamily is a key variation for thermo-responsive architecture and suggests a preference for generating diversity for local adaptation through signaling connectors.

Topological insulators with unique edge states have revolutionized the understanding of solid-state materials. Recently, higher-order topological insulators (HOTIs), which host both gapped edge states and in-gap corner/hinge states, protected concurrently by band topology, were predicted and observed in experiments, unveiling a new horizon beyond the conventional bulk-edge correspondence. However, the control and manifestation of band topology in a hierarchy of dimensions, which is at the heart of HOTIs, have not yet been witnessed. Here, we propose theoretically and observe experimentally that tunable two-dimensional sonic crystals can be versatile systems to visualize and harness higher-order topology. In our systems, the two-dimensional acoustic bands mimic the quantum spin Hall effect, while the resultant one-dimensional helical edge states are gapped due to broken space-symmetry and carry quantized Zak phases, which then lead to zero-dimensional topological corner states. We demonstrate that topological transitions in the bulk and edges can be triggered independently by tuning the geometry of the sonic crystals. With complementary experiments and theories, our study reveals rich physics in HOTIs, opening a new route towards tunable topological metamaterials where novel applications, such as the topological transfer of acoustic energy among two-, one- and zero-dimensional modes, can be achieved. By tuning the geometry of a two-dimensional sonic crystal, its one-dimensional helical edge states become gapped and zero-dimensional topological corner states emerge. The band topology is thus manifested in a hierarchy of dimensions.

The stretchable version of electronic circuits harnesses commercial chip scale components to achieve complex functionality and mechanical deformability, which represents an emerging technology to expand the application of conventional electronics on rigid wafers. The bottleneck lies in the lack of a robust approach for the collective integration of off-the-shelf components into a reliable system. In this study, an elastomeric composite material with skin-like mechanical responses and spatially heterogeneous rigidity is reported as an attractive platform for stretchable circuit systems. The approach utilizes a high modulus microstructure embedded in the matrix of a soft elastomer to achieve programmable mechanical properties, thereby offering selective strain isolation for fragile components and overall protection against excessive loads. A low cost procedure involving laser ablation and blade coating is established to create the composite material matching with the circuit design. In addition, ultrasonic atomization of liquid metal into microparticles allows flexible preparations of deformable conductors in the forms of interconnects and contacts. An LED matrix is demonstrated as a prototype circuit system with excellent durability to withstand repetitive stretching and external impacts. Stretchable circuit systems based on soft elastomeric composite materials may find potential uses in health monitoring, mechatronic prosthetics, and soft robotics.

At present, functionalities, miniaturization, and tunability are useful directions in the development of practical device applications for topological photonics and phononics. Atomically thin two-dimensional (2D) materials not only have excellent mechanical properties, but also have outstanding electrical, optical, and magnetic properties, making them great candidates for tunable microdevices via electrostatic forces, magnetoacoustic, or photoacoustic coupling, etc. In this paper, we propose an elastic topological insulator based on atomically thin 2D materials pinned on honeycomb-patterned substrates. Thanks to acoustic impedance mismatch between the suspended 2D materials and the rigid substrates, both topological edge states and corner states of elastic waves inside the 2D materials can be achieved, accompanied by a display of functional components, e.g., arbitrary waveguides, splitters, resonators. Significantly, all these components for elastic waves are frequency tunable, due to the electromechanical sensitivity of the 2D material. For example, a two-port high-Q bandpass filter is estimated to achieve 7.26% operating frequency shifting by applying only 5 V of gate voltage. These kinds of elastic topological materials and corresponding devices can strongly promote the development of 2D-material-based nanoelectromechanical systems and might have immediate applications in modern wireless communication technology at radio or microwave frequencies.

Higher-order topological insulators (HOTIs), a new horizon of topological phases of matter, host lower-dimensional corner or hinge states, providing important stepping stones to the realization of robust topological waveguides in higher dimensions. The nontrivial band topology that gives rise to the corner or hinge states is usually enabled by certain crystalline symmetries. As a result, higher-order topological boundary states are tied to specific corners or hinges, lacking the flexibility of switching and selecting. Here, we report the experimental realization of topologically switchable and valley-selective corner states in a two-dimensional sonic crystal. Such intriguing properties are enabled by exploiting the higher-order topology assisted with the valley degree of freedom. For this purpose, we realize a valley HOTI of second-order topology characterized by the nontrivial bulk polarization. Interestingly, the hosted corner states are found to be valley dependent and therefore enable flexible control and manipulation on the wave localization. Topological switch on or off and valley selection of the corner states are directly observed through spatial scanning of the sound field. We further design an arbitrary structure of complex patterns containing corners with various intersection angles, among which selected corners can be illuminated or darkened upon valley selection. The reported valley HOTI and the valley-selective corner states provide fundamental understanding on the interplay between higher-order topology and valley degree of freedom and pave the way for lower-dimensional valleytronics, which may find potential applications in integrated acoustics and photonics.

Macroscopic two-dimensional (2D) sonic crystals with inversion symmetry are studied to reveal higher-order topological physics in classical wave systems. By tuning a single geometry parameter, the band topology of the bulk and the edges can be controlled simultaneously. The bulk band gap forms an acoustic analog of topological crystalline insulators with edge states which are gapped due to symmetry reduction on the edges. In the presence of mirror symmetry, the band topology of the edge states can be characterized by the Zak phase, illustrating the band topology in a hierarchy of dimensions, which is the key feature of higher-order topological phenomena. Moreover, the edge bands undergo topological transitions without closing the bulk band gap, revealing rich topological physics in both the bulk and edges. We characterize the higher-order topological bands using symmetry indicators in the Brillouin zone and link the symmetry indicators with the corner charge---a corner topological index. This approach allows us to identify higher-order topological boundary states through symmetry properties of the Bloch bands. We then generalize the higher-order topological phenomena protected by the inversion symmetry to arch-shaped sonic crystals with nonsymmorphic symmetries where similar but slightly different topological phenomena are revealed. In these systems, the rich, multidimensional topological transitions can be exploited for topological transfer among 0D (corner), 1D (edge), and 2D (bulk) acoustic modes by tuning the geometry of acoustic metamaterials.

The discovery of quadrupole topology opens a new horizon in the study of topological phenomena. However, the existing experimental realizations of quadrupole topological insulators in symmorphic lattices with $\ensuremath{\pi}$ fluxes often break the protective mirror symmetry. Here, we present a theory for anomalous quadrupole topological insulators in nonsymmorphic crystals without flux using two-dimensional sonic crystals with $p4gm$ and $p2gg$ symmetry groups as concrete examples. We reveal that the anomalous quadrupole topology is protected by two orthogonal glide symmetries in square or rectangular lattices. The distinctive features of the anomalous quadrupole topological insulators include: (i) minimal four bands below the topological band gap, (ii) nondegenerate gapped Wannier bands and special Wannier sectors with gapped composite Wannier bands, and (iii) quantized Wannier band polarizations in these Wannier sectors. With no need for flux insertion, the protective glide symmetries are well preserved in the sonic-crystal realizations where higher-order topological transitions can be triggered by symmetry or geometry engineering.

Based on the propagation theory of acoustic waves in anisotropic media, the angular dispersion curves of SAW velocities propagated in some unusual oriented, such as (016)- and (331)-oriented, Body-Centered Cubic (BCC) single crystals are simulated using an optimized numerical method. Meanwhile, the angular dispersion curves of SAW velocities propagated in these unusual oriented BCC single crystals are measured by Impulsive Stimulated Scattering (ISS) laser ultrasonic method, which show that the measurement results are in good agreement with those of the simulations. By the optimized numerical method, the relationships between the temperature and the dispersion curves of SAW velocity propagated in these single crystals are also simulated.

Ghost imaging (GI) enables reconstruction of the image of an object by measuring the intensity correlation of two beams, neither of which independently carries the spatial characteristics of the object. By exploiting the space-time duality, GI has been extended from the spatial domain to the time domain, and has been successfully demonstrated in the optical regime. This article reports on the experimental demonstration of acoustic GI in the time domain. Using ultrasound instead of photons, we created high-quality ghost images of a temporal object, even in the presence of strong ambient noise. Our work offers a fresh approach for imaging disturbance-sensitive acoustic signals, and could open the gateway to identifying new approaches in acoustic sensing, dynamic imaging, and communications.

The principle of reciprocity underpins one of the fundamental effects in optics that signifies symmetric transmission with respect to the interchange of the source and observation points. Breaking reciprocity, however, enables additional functionalities and greatly enriches the applications of photonics in terms of nonreciprocal devices. Here, a realistic nanoscale cascaded-cavity system that envisages nonreciprocal optical isolation and efficient wavelength conversion based on spatiotemporally modulated index of refraction are proposed and numerically demonstrated. The on-chip, linear, magnetic-free nonreciprocal isolation and dynamically controllable wavelength conversion can be a promising candidate for silicon nanophotonic and optoelectronic devices.

The quantum spin Hall effect lays the foundation for the topologically protected manipulation of waves, but is restricted to one-dimensional-lower boundaries of systems and hence limits the diversity and integration of topological photonic devices. Recently, the conventional bulk-boundary correspondence of band topology has been extended to higher-order cases that enable explorations of topological states with codimensions larger than one such as hinge and corner states. Here, we demonstrate a higher-order quantum spin Hall effect in a two-dimensional photonic crystal. Owing to the non-trivial higher-order topology and the pseudospin-pseudospin coupling, we observe a directional localization of photons at corners with opposite pseudospin polarizations through pseudospin-momentum-locked edge waves, resembling the quantum spin Hall effect in a higher-order manner. Our work inspires an unprecedented route to transport and trap spinful waves, supporting potential applications in topological photonic devices such as spinful topological lasers and chiral quantum emitters., 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.

Magnetic insulating and exchange bias (EB) are two basic magnetic states with actual and potential applications in spintronic and magnonic devices. However, ferromagnetic insulators (FMIs) are rare, and it is even more challenging to obtain a FMI with large EB. In this paper, high performance of FMIs and EB in $\mathrm{LaMn}{\mathrm{O}}_{3}$:NiO nanocomposite epitaxial thin films is reported. The antiferromagnetic NiO nanoparticles, randomly embedded in a ferromagnetic $\mathrm{LaMn}{\mathrm{O}}_{3}$ matrix, enhance the robustness of the insulating state and result in an EB field as large as 1100 Oe. The simultaneously enhanced resistivity and EB are attributed to localized oxygen vacancy, preserved strain state, and increased ferromagnetic-antiferromagnetic interface ratio. This paper provides not only a material candidate for spintronics but also a referential strategy to design artificial materials with multifunctionality.

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.

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.

PdS is theoretically proposed to novel topological material with eight-band fermions. Here, PdS 1−δ crystals were successfully grown from KI as solvent by modified flux method. The single crystalline quality and compositional homogeneity of grown PdS 1−δ are characterized by X-ray diffraction and energy dispersion spectroscopy. Temperature dependent electrical transport property of PdS 1−δ demonstrates a semiconductor-like behavior. Analysis of temperature-dependent resistance indicates that there is variable-range-hopping behavior at low temperature. The clear negative MR of PdS 1−δ single crystals is measured at the low temperature (

Further improving electromechanical properties and overcoming relatively low Curie temperature (Tc) of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-100xPT) are still two scientific issues. Here, we demonstrate a stable coexistence of monoclinic-tetragonal (MC-T) phases in ZnO-modified PMN-32PT (PMN-32PT:xZnO) due to the diffusion-induced substitution of Zn2+ for Mg2+. The Curie temperature, saturated polarization, remnant polarization, piezoelectric coefficient (Tc, Ps, Pr, d33) are increased from (160 °C, 22.0 μC/cm2, 13.3 μC/cm2, 350 pC/N) for x = 0 to (180 °C, 30.3 μC/cm2, 22.4 μC/cm2, 470 pC/N) for x = 0.06. Moreover, the thermal stability is improved. After annealing at 150 °C, the x = 0.06 sample shows retrained d33 value of 209 pC/N, about 4 times larger than that of x = 0 counterpart. The improved properties are attributed to the substituting increased polar nanoregions and easy domain switching in MC phase.

Acoustics is a classical field of study that has witnessed tremendous developments over the past 25 years. Driven by the novel acoustic effects underpinned by phononic crystals with periodic modulation of elastic building blocks in wavelength scale and acoustic metamaterials with localized resonant units in subwavelength scale, researchers in diverse disciplines of physics, mathematics, and engineering have pushed the boundary of possibilities beyond those long held as unbreakable limits. More recently, structure designs guided by the physics of graphene and topological electronic states of matter have further broadened the whole field of acoustic metamaterials by phenomena that reproduce the quantum effects classically. Use of active energy-gain components, directed by the parity–time reversal symmetry principle, has led to some previously unexpected wave characteristics. It is the intention of this review to trace historically these exciting developments, substantiated by brief accounts of the salient milestones. The latter can include, but are not limited to, zero/negative refraction, subwavelength imaging, sound cloaking, total sound absorption, metasurface and phase engineering, Dirac physics and topology-inspired acoustic engineering, non-Hermitian parity–time synthetic active metamaterials, and one-way propagation of sound waves. These developments may underpin the next generation of acoustic materials and devices, and offer new methods for sound manipulation, leading to exciting applications in noise reduction, imaging, sensing and navigation, as well as communications.

Light beams with helical wave fronts, also called optical vortices, have attracted great interest in the community of optics and photonics. They provide an additional degree of freedom for light manipulation, leading to wide-ranging potential applications in micro-particle trapping, optical microscopy, and even quantum information processing. Recently, metallic microstructures are introduced to confine the plasmonic vortices into deep subwavelength dimension, which benefits photonic integration on chip. In this Letter, exploiting the excitation of spoof surface plasmon, we experimentally demonstrate the near-field optical vortices with tunable topological charges supported by a single metaparticle in the microwave regime. These microwave plasmonic-like vortices are excited by surface waves with a spatial asymmetric distribution of electromagnetic field, which are launched by a metallic comb-shaped waveguide. Experimental characterization of highly localized and controllable near-field vortices with the nature of deep subwavelength confirms the numerical simulation. In addition, an equivalent physical model based on the coupled mode theory is proposed to understand the generation mechanism of these spoof plasmonic vortices. Our approach offers an efficient way to generate deterministic subwavelength optical vortices, which provides the potential for critical vortex elements on photonic integrated chip.

The topological phase of matter, originally proposed and first demonstrated in fermionic electronic systems, has drawn considerable research attention in the past decades due to its robust transport of edge states and its potential with respect to future quantum information, communication, and computation. Recently, searching for such a unique material phase in bosonic systems has become a hot research topic worldwide. So far, many bosonic topological models and methods for realizing them have been discovered in photonic systems, acoustic systems, mechanical systems, etc. These discoveries have certainly yielded vast opportunities in designing material phases and related properties in the topological domain. In this review, we first focus on some of the representative photonic topological models and employ the underlying Dirac model to analyze the edge states and geometric phase. On the basis of these models, three common types of two-dimensional topological photonic systems are discussed: 1) photonic quantum Hall effect with broken time-reversal symmetry; 2) photonic topological insulator and the associated pseudo-time-reversal symmetry-protected mechanism; 3) time/space periodically modulated photonic Floquet topological insulator. Finally, we provide a summary and extension of this emerging field, including a brief introduction to the Weyl point in three-dimensional systems.

Recently, transition metal pentatellurides MTe5 (M = Zr, Hf) have inspired intensive research effort. Being predicted to be quantum spin Hall insulators (QSHI) with the bulk gap up to hundreds of meVs, it could lead to promising applications at unprecedented high temperature compared with previously discovered QSHI (e.g. HgTe/CdTe or InAs/GaSb quantum wells). However, the experimental works soon followed illustrated considerable discrepancies regarding to whether MTe5 compounds possess a full bulk gap, making their topological nature (topological insulators or Dirac semimetals) illusive. In this work, combining investigations of angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM), we systematically studied the electronic properties of ZrTe5. In intrinsic samples, we observed little evidence for the existence of topological surface states or large bulk gap. With bulk and surface doping to adjust the position of the Fermi-level, ARPES spectra indicate gapless and highly linear dispersions at the valance band top, in consistence with the STM measurements that show a V-shaped total density of states near the Fermi-level (i.e. suggesting a gapless nature of the electronic structure of ZrTe5). Moreover, near the terrace edge on the surface, we observed non-zero DOS, indicating the existence of edge states.

Transition metal compounds with quasi-two-dimensional structure demonstrate a series of un-precedent quantum phases, such as topological insulator, topological phase transition under thermal/pressure stimuli, which is attributed to delicate interplay among interlayer coupling, spin-orbit coupling and stoichiometry. Here, Cu2TlSe2 and Cu2TlTe2 crystals were successfully synthesized by Bridgeman method. Highly crystalline quality of these samples is verified by X-ray diffraction and microstructural characterization. Temperature-dependent-Hall-resistivity shows that Cu2TlSe2 is hole-like and Hall resistivity is in-sensitive to temperature; while Hall resistivity of Cu2TlTe2 is positive at room temperature and change to negative at 30 K. Combined experimental results and electronic band structures calculated by first-principles method, it is revealed that Cu2TlSe2 is a metal, but Cu2TlTe2 is a semi-metal. This work demonstrates the rich physical phases of layered transition metal compounds under the interplay among interlayer coupling, spin-orbit coupling and stoichiometry.

Bulk silicon possesses no second-order susceptibility (χ(2)), inhibiting second-order nonlinear processes in the emerging silicon photonic platform. Here, we propose a method to overcome this limitation by enabling a third-order (χ(3)) nonlinear mixing scheme between optical waves and an externally applied static electric field inside a silicon waveguide. We show in theory that facilitated by a modal phase-matching scheme efficient second-harmonic generation can be realized under an applied voltage of 65 V, giving rise to an equivalent χ(2) = 4.7 pm/V. We also show that unlike the classical second-harmonic generation, the wavelengths of phase-matched pump and second-harmonic waves are pump-power dependent due to the χ (3) nature of this process.

A long-term goal of phononic communication is controlled transport of elastic wave signals with improved robustness and enhanced information capacity, but existing approaches suffer from unwanted backscattering by defects and disorder that may substantially reduce the transmission rate, or even disable a data channel. This study uses the robust edge states along the interfaces between distinct topological classes to make progress. These fault-tolerant edge channels are protected jointly by both pseudospin and valley degrees of freedom, naturally providing doubled information carriers within every channel, and may serve as a building block for large-scale phononic circuits and networks.

We establish the bilayer non-Hermitian theory with interlayer coupling between two graphenelike lattices described by non-Hermitian Hamiltonians. Two exceptional rings (ERs) and an exceptional concentric ring (ECR) in this system are discovered. A topological classification has been identified for such non-Hermitian Hamiltonians via their global topological invariants. We find that two ERs and the ECR correspond to the global ${\mathbb{Z}}_{3}$ topological invariant $V=+1$ and $V=\ensuremath{-}1$, respectively, whose topological properties are determined by the four-level bands and go beyond the topological properties of a single ER. It is shown that in contrast to the Hermitian case, the topological surface arcs with gain and loss are both present and redistributed in the two ERs and the ECR systems. We further propose an experimental design with bilayer photonic crystals (PCs) to realize the ECR. Our work can potentially pave the way for unveiling the unusual topological properties in such stacked two-dimensional materials and trigger further theoretical and experimental investigations.

Misfit-layered compounds constitute a significant component in the development of thermoelectric materials. Prominent thermoelectric properties arise from their low lattice thermal conductivity, which was supposed to be a consequence of intense phonon scattering at the misfit interfaces. Nevertheless, in most misfit compounds, the coexistence of van der Waals interfaces makes it hard to reveal the effect of misfit interfaces individually. Here, we investigate the impact of misfit interfaces and Bi–O/Bi–O interfaces on the thermal transport of a series of single crystals, including layered KxCoO2 (KCO, reference), misfit-layered compounds Ca3Co4O9 (CCO, with misfit interfaces) and Bi2Ca2Co2Oy (BCCO, with misfit interfaces and Bi–O/Bi–O interfaces) and layered compound Bi2Sr2CaCu2Oy (BSCCO, with Bi–O/Bi–O interfaces). Ultralow thermal conductivity approaching the theoretically predicted thermal conductivity minimum (∼0.28 W m−1 K−1 at 300 K) is achieved only with the existence of Bi–O/Bi–O interfaces with van der Waals interactions. Further analyses of the phonon scattering mechanisms verify that the strength of phonon Umklapp scattering and phonon–boundary (interface) scattering is comparable in KCO and CCO, while in BCCO and BSCCO phonon–boundary scattering dominates. Furthermore, the characteristic lengths for phonon–boundary scattering in BCCO and BSCCO are one magnitude lower than those of KCO and CCO, which proves the remarkable effect of the Bi–O/Bi–O interfaces in reducing thermal conductivity. Our work demonstrates the vital impact of interfaces with strong van der Waals interactions on the thermal conductivity reduction, and provides inspiration for the design of advanced thermoelectric materials.

International audience; Poor wettability and acoustic mismatch between diamond and copper cause low interface thermal conductance and thus low thermal conductivity in their composites. In this work, beyond widely used strategies such as surface metallization and matrix alloying, in-situ grown graphene is introduced as a highly effective interlayer. The positive role of graphene on improving wetting between diamond and copper was supported by the increase of relative density, fractured surface morphology and interface microstructure. Thanks to the improved wetting and mitigated acoustic mismatch between diamond and copper, the interfacial thermal conductance is increased by ~3.7 times in the diamond/graphene/copper composite as indicated by differential effective medium calculation. Such a positive role of graphene 2 interlayer also agrees with the results from the time-domain thermoreflectance measurements. As a result, the thermal conductivity of the diamond/graphene/copper composite is 61% higher than that of the counterpart without graphene interlayer. This study provides a new approach for interface modification by 2D materials for a high TC of diamond/copper composite beyond surface metallization and matrix alloying.

Bound states in the continuum (BICs) in photonic crystals represent the unique solutions of wave equations possessing an infinite quality-factor. We design a type of bilayer photonic crystal and study the influence of symmetry and coupling between TE and TM polarizations on BICs. The BIC modes possess $C_{3v}$ symmetry in the x-y plane while the mirror-flip symmetry in the z-direction is broken, and they provide selective coupling into different layers by varying frequency. The enhanced TE-TM coupling due to broken mirror-flip symmetry in the z-direction gives rise to high-Q factor BIC states with unique spatial characteristics. We show the emergence of such BIC states even in the presence of coupling between the TE- and TM-like modes, which is different from the existing single polarization BIC models. We propose to study BICs in multilayer systems, and the results may be helpful in designing photonic settings to observe and manipulate BICs with various symmetries and polarizations for practical applications., 15 pages, 6 figures

In this paper, we introduce a method to analyze three-phase inverters with current control as equivalent circuits. In contrast to existing methods, both the averaged power stage model and its closed-loop controller are represented as a single unified circuit. Since the complete system can be examined as one equivalent circuit, we can glean several insights on design and operation; particularly relating to the time scales at which the controller tracks reference signals and the ability to reject disturbances. We leverage the insights afforded by this general approach to outline design strategies for controllers in both synchronous and stationary reference frames.

Recently, the oxide semiconductor $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ nanoplates with an ultrahigh mobility demonstrated superior ultrafast photoelectronic properties of which physical origins are hotly studied theoretically and experimentally. Here we grew the $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ crystals via the chemical vapor transport method. The $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ crystal exhibits an ultrahigh Hall mobility $(\ensuremath{\sim}2.24\ifmmode\times\else\texttimes\fi{}{10}^{5}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}{\mathrm{V}}^{\ensuremath{-}1}{\mathrm{s}}^{\ensuremath{-}1}\mathrm{at}\phantom{\rule{0.16em}{0ex}}2\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ and a giant magnetoresistance $(\mathrm{MR}\ensuremath{\sim}0.9\ifmmode\times\else\texttimes\fi{}{10}^{4}%\phantom{\rule{4pt}{0ex}}\mathrm{at}\phantom{\rule{4pt}{0ex}}9\phantom{\rule{0.16em}{0ex}}\mathrm{T}\phantom{\rule{4pt}{0ex}}\mathrm{and}\phantom{\rule{4pt}{0ex}}2\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ that are comparable with those in $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ nanoplates. MR data clearly shows Shubnikov--de Haas (SdH) oscillations. Systematic analysis of SdH oscillation verifies that the electrical carrier in $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ is a conventional Schr\"odinger fermion and that the Fermi surface of $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ is quasi-two-dimensional-like. Remarkably, the resistivity of $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ is quadratically dependent on temperature from 2 to 300 K, inferring the electron-electron scattering in $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$. Kohler's rule analysis of temperature-dependent MR verifies only electron-electron scattering dominated by the electrical and magnetotransport properties of $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$. Combining first-principle calculations and empirical Landau Fermi liquid theory, we substantiate that the Fermi surface of the electron in $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ is an elongated ellipsoid, as well as that the electron-electron interaction and screening length of $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ are estimated as 7.49 eV and 5.53 \AA{}, respectively. These values are quite large among the conventional doped semiconductors. Our study may shed more light on the physical origin of the ultrafast photoelectric response of $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$.

Heat stress has become a major threat to crop production due to global warming; however, the mechanisms underlying plant high-temperature sensing are not well known. In plants, the membrane-anchored receptor-like kinases (RLKs) relay environmental signals into the cytoplasm. In a previous study, we isolated a wall-associated RLK-like (WAKL) gene CaWAKL20 from pepper (Capsicum annuum L.). Here, the amino acid sequence of CaWAKL20 was characterized and found to consist of conserved domains of WAK/WAKL family, including an extracellular region containing a GUB-WAK binding domain and a degenerated EGF2-like domain; a transmembrane region; and an intercellular region with an STKc catalytic domain. Moreover, CaWAKL20 transcription was inhibited by heat stress, whereas it was induced by both ABA and H2O2 treatments. Silencing of CaWAKL20 enhanced pepper thermotolerance, while overexpression decreased Arabidopsis thermotolerance. Additionally, Arabidopsis lines overexpressing CaWAKL20 showed less sensitivity to ABA during seed germination and root growth. Finally, the survival rate of Arabidopsis seedlings under heat stress treatment was enhanced by ABA pre-treatment, while it was compromised by the overexpression of CaWAKL20. Furthermore, the heat-induced expression of several ABA-responsive genes and some key regulator genes for thermotolerance was decreased in Arabidopsis CaWAKL20-overexpression lines. These results suggest that CaWAKL20 negatively modulates plant thermotolerance by reducing the expression of ABA-responsive genes, laying a foundation for further investigation into the functional mechanisms of WAKs/WAKLs in plants undergoing environmental stresses.

Wave trapping and manipulation are at the heart of modern integrated photonics and acoustics. Grand challenges emerge on increasing the integration density and reducing the wave leakage/noises due to fabrication imperfections, especially for waveguides and cavities at subwavelength scales. The rising of robust wave dynamics based on topological mechanisms offers possible solutions. Ideally, in a three-dimensional (3D) topological integrated chip, there are coexisting robust two-dimensional (2D) interfaces, one-dimensional (1D) waveguides and zero-dimensional (0D) cavities. Here, we 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 system. Such an unprecedented phenomenon is triggered by the higher-order topology in simple-cubic sonic crystals and protected by the space group \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${P}_{m\bar{3}m}$$\end{document}Pm3 ¯m. Our study opens up a new regime for multidimensional wave trapping and manipulation at subwavelength scales, which may inspire future technology for integrated acoustics and photonics., 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.

Time-reversal symmetry (TRS) of electrons is associated with an anti-unitary operator with T 2 = &minus, 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 = &minus, 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.

Acoustic analogue computation and signal processing are of great significance, however, it's challenging to realize the acoustic computing devices because of their limitations of single function and complex structure. In this paper, an acoustic multifunctional device, which can gate or amplify acoustic waves without resorting to altering the frequency and structure using a passive acoustic parity-time (PT)-symmetric metamaterial, is realized theoretically and experimentally. The metamaterial is constructed by five lossless-loss periodically distributed media which are modulated to achieve the passive PT symmetry. At the coherent perfect absorber (CPA)-emitter point in the broken PT-symmetric phase, the logic gates (AND, OR, XOR and NOT) and small signal amplifier are realized in a single system by adjusting the phase and amplitude differences between two incoming beams, respectively. This work provides a new route for the connection between the PT symmetry and the acoustic metamaterial, which has great potential applications in acoustic modulation and acoustic multifunctional device.

Frontier investigations on a contemporary family of materials comprise a new class of topological materials that have been discovered in three dimensional (3D) semimetallic crystals. Beyond already unconventional topological quasiparticles in Dirac and Weyl semimetals, nodal-line semimetals provide an even richer platform encompassing robust band-touching manifolds and exotic transport properties. Classical configurations including artificial crystals have emerged as popular systems not only to replicate these new properties in wave-based scenarios, but particularly also to ease experimental complexities of electronic systems and to permit topological tuning via variable geometrical designs. Sonic crystals are one of such example, in which dissimilar fluid or rigid inclusions or channels are combined to tailor the acoustic material response at will. Here, we design a cubic lattice of guiding channels allowing us to map topological characteristics of quasi-particles excitations to audible sound properties. Simply by varying the cross section of these channels, we bring forward multiple phase transitions among four different interlaced nodal features, which resemble the knitting of 3D Bloch-bulk bands in momentum space. One nodal attribute appears to feature an acoustic version of directional massless Dirac fermions, which is experimentally characterized and displays linear crossing in one direction and flat bands in the perpendicular one, enabling strongly focused and collimated sound beams, thanks to this peculiar dispersion. J.C. acknowledges the support from the European Research Council (ERC) through the Starting Grant No. 714577 PHONOMETA and from the MINECO through a Ramón y Cajal grant (Grant No. RYC-2015-17156). X.J.Z. M.H.L. and Y.F.C. acknowledge the support from the National Key R & D Program of China (2017YFA0303702, 2018YFA0306200), the National Natural Science Foundation of China (Grant No. 51902151, 11625418, 11890700, 51732006 and 51902151), the Natural Science Foundation of Jiangsu Province (Grant No. BK20190284) and the Fundamental Research Funds for the Central Universities (14380165). Publicado

Erbium doped amorphous alumina thin films were fabricated using Co-sputtering technique in various depositions runs with varying parameters for optimizing the deposition parameters to obtain the films with best optical performance. The main subject of investigation includes the effects of change in various deposition parameters such as substrate heating, radio frequency (RF) power and oxygen pressure inside the chamber while deposition. High quality as-deposited films with various Er concentrations and low carbon content have been confirmed by XPS. Substrate heating ∼500 °C was found to be very effective in getting highly dense films with high refractive index of 1.70 at 1530–1570 nm emission band. The Er3+-doped films showed very intense near-infrared luminescence peak at 1550 nm even without any post-deposition annealing treatment.

Stresses caused by heat and Phytophthora capsici infection reduce pepper (Capsicum annuum) yields; however, little is known about their combined effects on pepper. In this study, the combination of heat and P. capsici infection resulted in worse symptoms, including increased heat stress injury, cell death, relative electrical conductivity, and decreased root activity, than either individual stress. The symptoms were more obvious in the susceptible pepper cultivar ‘Early Calwonder’ (EC) than in the resistant landrace line ‘Criollo de Morelos 334’ (CM334). Under heat stress alone, the expression levels of three tested C. annuum heat-shock protein (CaHSP) genes were enhanced in both ‘CM334’ and ‘EC’; however, under the combined stress, their expression levels increased in ‘CM334,’ but decreased in ‘EC.’ Among four defense-related genes, under stress treatments, only two were up-regulated in ‘CM334’ and ‘EC,’ respectively, and both showed higher levels under the combined stress than under the individual stresses. Under the combined stress, the expression levels of three tested Ca2+-signaling pathway genes were enhanced in ‘EC,’ but inhibited in ‘CM334’ compared with either heat or P. capsici infection. Compared with the effects caused by either heat or P. capsici infection, the CaWRKY expression levels were restored to nearly normal levels under the combined stress, and the number of up-regulated genes was higher in ‘CM334’ than in ‘EC.’ Thus, the molecular responses of pepper to the combined stress of heat and P. capsici infection are different from those caused by individual stresses, and the stresses interaction is different between resistant and susceptible pepper germplasms.

Strategic manipulation of wave and particle transport in various media is the key driving force for modern information processing and communication. In a strongly scattering medium, waves and particles exhibit versatile transport characteristics such as localization, tunnelling with exponential decay, ballistic, and diffusion behaviours due to dynamical multiple scattering from strong scatters or impurities. Recent investigations of graphene have offered a unique approach, from a quantum point of view, to design the dispersion of electrons on demand, enabling relativistic massless Dirac quasiparticles, and thus inducing low-loss transport either ballistically or diffusively. Here, we report an experimental demonstration of an artificial phononic graphene tailored for surface phonons on a LiNbO3 integrated platform. The system exhibits Dirac quasiparticle-like transport, that is, pseudo-diffusion at the Dirac point, which gives rise to a thickness-independent temporal beating for transmitted pulses, an analogue of Zitterbewegung effects. The demonstrated fully integrated artificial phononic graphene platform here constitutes a step towards on-chip quantum simulators of graphene and unique monolithic electro-acoustic integrated circuits.

Significance Topological insulators are first discovered in electronic systems. A key factor is the Kramers doublet for the spin-1/2 electrons under fermionic time-reversal symmetry T f 2 = − 1 . Unlike electrons, photons are massless bosons with spin-1. Therefore, the Kramers degeneracy theorem cannot readily apply to photons under the bosonic time-reversal symmetry. So far, there has been no coherent physical explanation for the symmetry protection mechanism behind the photonic topological insulator. Here, we design a photonic topological insulator that violates the bosonic time-reversal symmetry but complies with a fermionic-like pseudo time-reversal symmetry. The analyses and results, through comprehensive investigations on the properties of edge states, validate that the topological edge states are, in fact, protected by the fermionic-like pseudo time-reversal symmetry T p ( T p 2 = − 1 ).

Van der Waals junctions of two-dimensional materials with an atomically sharp interface open up unprecedented opportunities to design and study functional heterostructures. Semiconducting transition metal dichalcogenides have shown tremendous potential for future applications due to their unique electronic properties and strong light-matter interaction. However, many important optoelectronic applications, such as broadband photodetection, are severely hindered by their limited spectral range and reduced light absorption. Here, we present a p-g-n heterostructure formed by sandwiching graphene with a gapless bandstructure and wide absorption spectrum in an atomically thin p-n junction to overcome these major limitations. We have successfully demonstrated a MoS2-graphene-WSe2 heterostructure for broadband photodetection in the visible to short-wavelength infrared range at room temperature that exhibits competitive device performance, including a specific detectivity of up to 1011 Jones in the near-infrared region. Our results pave the way toward the implementation of atomically thin heterostructures for broadband and sensitive optoelectronic applications., Submitted to Nano Letters; 25 pages, 4 figures, 7 supplementary figures