This article reviews recent developments in the non-Hermitian skin effect (NHSE), particularly on its rich interplay with topology. The review starts off with a pedagogical introduction on the modified bulk-boundary correspondence, the synergy and hybridization of NHSE and band topology in higher dimensions, as well as, the associated topology on the complex energy plane such as spectral winding topology and spectral graph topology. Following which, emerging topics are introduced such as non-Hermitian criticality, dynamical NHSE phenomena, and the manifestation of NHSE beyond the traditional linear non-interacting crystal lattices, particularly its interplay with quantum many-body interactions. Finally, we survey the recent demonstrations and experimental proposals of NHSE.
Atomically thin two-dimensional (2D) transition metal dichalcogenides (TMDCs) have stimulated enormous research interest due to rich phase structure, high theoretical carrier mobility and layer-dependent bandgap. In view of the close correlation between defects and properties in 2D TMDCs, more attentions have been paid on the defect engineering in recent years, however the mechanism is still unclear. Herein, we review the critical progress of defect engineering and provide an extensive way to modulate the properties depressed by defects. To insight into the defect engineering, we firstly introduce two common kinds of defects during the growth progress of TMDCs and the possible distribution of energy levels those defects could induce. Then, various methods to improve point defects and grain boundaries during the period of growth are discussed intensively, with the assistance of which more large-area TMDCs films can be obtained. Considering the defects in TMDCs are inevitable regardless of concentration, we also highlight strategies to heal the defects after growth. Through dry methods or wet methods, the chalcogen vacancies can be repaired and thus, the performance of electronic device would be significantly enhanced. Finally, we propose the challenges and prospective for defect engineering in 2D TMDCs materials to support the optimization of device and lead them to wide applied fields.
Two-dimensional (2D) transition metal dichalcogenides (TMDs) with fascinating electronic energy band structures, rich valley physical properties and strong spin–orbit coupling have attracted tremendous interest, and show great potential in electronic, optoelectronic, spintronic and valleytronic fields. Stacking 2D TMDs have provided unprecedented opportunities for constructing artificial functional structures. Due to the low cost, high yield and industrial compatibility, chemical vapor deposition (CVD) is regarded as one of the most promising growth strategies to obtain high-quality and large-area 2D TMDs and heterostructures. Here, state-of-the-art strategies for preparing TMDs details of growth control and related heterostructures construction via CVD method are reviewed and discussed, including wafer-scale synthesis, phase transition, doping, alloy and stacking engineering. Meanwhile, recent progress on the application of multi-functional devices is highlighted based on 2D TMDs. Finally, challenges and prospects are proposed for the practical device applications of 2D TMDs.
In the macroscopic world, we can obtain some important information through the vibration of objects, that is, listening to the sound. Likewise, we can also get some information of the nanoparticles that we want to know by the means of “listening” in the microscopic world. In this review, we will introduce two sensing methods (cavity optomechanical sensing and surface-enhanced Raman scattering sensing) which can be used to detect the nanoparticles. The cavity optomechanical systems are mainly used to detect sub-gigahertz nano particle or cavity vibrations, while surface-enhanced Raman scattering is a well-known technique to detect molecular vibrations whose frequency generally exceeds terahertz. Therefore, the vibrational information of nanoparticles from low-frequency to high-frequency could be obtained by these two methods. The size of the viruses is at the nanoscale and we can regard it as a kind of nanoparticles. Rapid and ultrasensitive detection of the viruses is the key strategies to break the spread of the viruses in the community. Cavity optomechanical sensing enables rapid, ultrasensitive detection of nanoparticles through the interaction of light and mechanical oscillators and surface-enhanced Raman scattering is an attractive qualitatively analytical technique for chemical sensing and biomedical applications, which has been used to detect the SARS-CoV-2 infected. Hence, investigation in these two fields is of vital importance in preventing the spread of the virus from affecting human’s life and health.
Conduction filament formation, redox reaction, and mobile ion migration in solid electrolytes underpin the memristive devices, all of which are partially influenced or fully dominated by the moisture. The moisture-based physical-chemistry mechanism provides an electric tunable method to create enough dissociate conductance states for neuromorphic computing, but overconcentration moisture will corrode electrode and then causes device invalidation. This perspective goal is that surveys the moisture-dependency of dynamic at interfaces or/and switching function layer, clarifies the bottlenecks that the memristive device facing in terms of water molecule-related reaction, and gives the possible solutions.
One variety of ferroelectricity that results from lateral relative movements between the adjacent atomic layers is referred to as sliding ferroelectricity, which generates an interfacial charge transfer and hence a polarization reversal. The mechanism of sliding ferroelectricity existent in van der Waals crystals is quite distinct from the conventional ferroelectric switching mechanisms mediated by ion displacement. It creates new possibilities for the design of two-dimensional (2D) ferroelectrics since it can be achieved even in non-polar systems. Before 2D ferroelectrics can be widely employed for practical implementations, however, there is still significant work to be done on several fronts, such as exploring ferroelectricity possibly in more potential 2D systems. Here, we report the experimental observation of room-temperature robust vertical ferroelectricity in layered semiconducting rhenium diselenide (ReSe2), a representative member of the transition metal dichalcogenides material family, based on a combined research of nanoscale piezoresponse and second harmonic generation measurements. While no such ferroelectric behavior was seen in 1L ReSe2, 2L ReSe2 exhibits vertical ferroelectricity at ambient environment. Based on density-functional theory calculations, we deduce that the microscopic origin of ferroelectricity for ReSe2 is uncompensated vertical charge transfer that is dependent on in-plane translation and switchable upon interlayer sliding. Our findings have important ramifications for the ongoing development of sliding ferroelectricity since the semiconducting properties and low switching barrier of ReSe2 open up the fascinating potential for functional nanoelectronics applications.
The three-dimensional electronic structure and the nature of Ce 4f electrons of the Kondo insulator CeRu4Sn6 are investigated by angle-resolved photoemission spectroscopy, utilizing tunable photon energies. Our results reveal (i) the three-dimensional k-space nature of the Fermi surface, (ii) the localized-to-itinerant transition of f electrons occurs at a much high temperature than the hybridization gap opening temperature, and (iii) the “relocalization” of itinerant f-electrons below 25 K, which could be the precursor to the establishment of magnetic order.
Bilayer (BL) molybdenum disulfide (MoS2) is one of the most important electronic structures not only in valleytronics but also in realizing twistronic systems on the basis of the topological mosaics in moiré superlattices. In this work, BL MoS2 on sapphire substrate with 2H-stacking structure is fabricated. We apply the terahertz (THz) time-domain spectroscopy (TDS) for examining the basic optoelectronic properties of this kind of BL MoS2. The optical conductivity of BL MoS2 is obtained in temperature regime from 80 K to 280 K. Through fitting the experimental data with the theoretical formula, the key sample parameters of BL MoS2 can be determined, such as the electron density, the electronic relaxation time and the electronic localization factor. The temperature dependence of these parameters is examined and analyzed. We find that, similar to monolayer (ML) MoS2, BL MoS2 with 2H-stacking can respond strongly to THz radiation field and show semiconductor-like optoelectronic features. The theoretical calculations using density functional theory (DFT) can help us to further understand why the THz optoelectronic properties of BL MoS2 differ from those observed for ML MoS2. The results obtained from this study indicate that the THz TDS can be applied suitably to study the optoelectronic properties of BL MoS2 based twistronic systems for novel applications as optical and optoelectronic materials and devices.
Materials with large intrinsic valley splitting and high Curie temperature are a huge advantage for studying valleytronics and practical applications. In this work, using first-principles calculations, a new Janus TaNF monolayer is predicted to exhibit excellent piezoelectric properties and intrinsic valley splitting, resulting from the spontaneous spin polarization, the spatial inversion symmetry breaking and strong spin−orbit coupling (SOC). TaNF is also a potential two-dimensional (2D) magnetic material due to its high Curie temperature and large magnetic anisotropy energy. The effective control of the band gap of TaNF can be achieved by biaxial strain, which can transform TaNF monolayer from semiconductor to semi-metal. The magnitude of valley splitting at the CBM can be effectively tuned by biaxial strain due to the changes of orbital composition at the valleys. The magnetic anisotropy energy (MAE) can be manipulated by changing the energy and occupation (unoccupation) states of d orbital compositions through biaxial strain. In addition, Curie temperature reaches 373 K under only −3% biaxial strain, indicating that Janus TaNF monolayer can be used at high temperatures for spintronic and valleytronic devices.
Adenosine triphosphate (ATP) is closely related to the pathogenesis of certain diseases, so the detection of trace ATP is of great significance to disease diagnosis and drug development. Graphene field-effect transistors (GFETs) have been proven to be a promising platform for the rapid and accurate detection of small molecules, while the Debye shielding limits the sensitive detection in real samples. Here, a three-dimensional wrinkled graphene field-effect transistor (3D WG-FET) biosensor for ultra-sensitive detection of ATP is demonstrated. The lowest detection limit of 3D WG-FET for analyzing ATP is down to 3.01 aM, which is much lower than the reported results. In addition, the 3D WG-FET biosensor shows a good linear electrical response to ATP concentrations in a broad range of detection from 10 aM to 10 pM. Meanwhile, we achieved ultra-sensitive (LOD: 10 aM) and quantitative (range from 10 aM to 100 fM) measurements of ATP in human serum. The 3D WG-FET also exhibits high specificity. This work may provide a novel approach to improve the sensitivity for the detection of ATP in complex biological matrix, showing a broad application value for early clinical diagnosis and food health monitoring.
Band mapping is widely used in various scenarios of cold atom physics to measure the quasi-momentum distribution and band population. However, conventional methods fail in strongly interacting systems. Here we propose and experimentally realize a novel scheme of band mapping that can accurately measure the quasi-momentum of interacting many-body systems. Through an anisotropic control in turning down the three-dimensional optical lattice, we can eliminate the effect of interactions on the band mapping process. Then, based on a precise measurement of the quasi-momentum distribution, we introduce the incoherent fraction as a physical quantity that can quantify the degree of incoherence of quantum many-body states. This method enables precise measurement of processes such as the superfluid to Mott insulator phase transition. Additionally, by analyzing the spatial correlation derived from the quasi-momentum of superfluid-Mott insulator phase transitions, we obtain results consistent with the incoherent fraction. Our scheme broadens the scope of band mapping and provides a method for studying quantum many-body problems.
We report an experimental study of magnetic-field-sensitive multi-wave interference, realized in a three-wave RF-atom system. In the F = 1 hyperfine level of the
Photonic moiré superlattice as an emerging platform of flatbands can tightly confine the light inside the cavity and has important applications not only in linear optics but also in nonlinear optics. In this paper, we numerically investigate the third- and fifth-order harmonic generation (THG and FHG) in photonic moiré superlattices fabricated by the nonlinear material silicon. The high conversion efficiency of THG and FHG is obtained at a relatively low intensity of fundamental light, e.g., the maximum conversion efficiency of THG and FHG arrives even up to be 10−2 and 10−9 at the fundamental intensity of 30 kW/m2, respectively, in the moiré superlattice of near flat band formed by the twist angle 6.01°. The results indicate the photonic moiré superlattice of a high-quality factor and flatbands is a promising platform for efficient nonlinear processes and advanced photonic devices.
Photonic graphene, possesses a honeycomb-like geometric structure, provides a superior platform for simulating photonic bandgap, Dirac physics, and topological photonics. Here, the photonic graphene with reconfigurable geometric structures is demonstrated in a 5S1/2 − 5P3/2 − 5D5/2 cascade-type 85Rb atomic ensembles. A strong hexagonal-coupling field, formed by the interference of three identical coupling beams, is responsible for optically inducing photonic graphene in atomic vapor. The incident weak probe beam experiences discrete diffraction, and the observed pattern at the output plane of vapor cell exhibits a clear hexagonal intensity distribution. The complete photonic graphene geometries from transversely stretched to longitudinally stretched are conveniently constructed by varying the spatial arrangement of three coupling beams, and the corresponding diffraction patterns are implemented theoretically and experimentally to map these distorted geometric structures. Moreover, the distribution of lattice sites intensity in photonic graphene is further dynamically adjusted by two-photon detuning and the coupling beams power. This work paves the way for further investigation of light transport and graphene dynamics.
We investigate the itinerant ferromagnetism in a dipolar Fermi atomic system with the anisotropic spin−orbit coupling (SOC), which is traditionally explored with isotropic contact interaction. We first study the ferromagnetism transition boundaries and the properties of the ground states through the density and spin-flip distribution in momentum space, and we find that both the anisotropy and the magnitude of the SOC play an important role in this process. We propose a helpful scheme and a quantum control method which can be applied to conquering the difficulties of previous experimental observation of itinerant ferromagnetism. Our further study reveals that exotic Fermi surfaces and an abnormal phase region can exist in this system by controlling the anisotropy of SOC, which can provide constructive suggestions for the research and the application of a dipolar Fermi gas. Furthermore, we also calculate the ferromagnetism transition temperature and novel distributions in momentum space at finite temperature beyond the ground states from the perspective of experiment.
As an emerging group III−VI semiconductor two-dimensional (2D) material, gallium selenide (GaSe) has attracted much attention due to its excellent optical and electrical properties. In this work, high-quality epitaxial growth of few-layer GaSe nanoflakes with different thickness is achieved via chemical vapor deposition (CVD) method. Due to the non-centrosymmetric structure, the grown GaSe nanoflakes exhibits excellent second harmonic generation (SHG). In addition, the constructed GaSe nanoflake-based photodetector exhibits stable and fast response under visible light excitation, with a rise time of 6 ms and decay time of 10 ms. These achievements clearly demonstrate the possibility of using GaSe nanoflake in the applications of nonlinear optics and (opto)-electronics.
Here, we study the controllable optical responses in a two-cavity optomechanical system, especially on the perfect optomechanically induced transparency (OMIT) in the model which has never been studied before. The results show that the perfect OMIT can still occur even with a large mechanical damping rate, and at the perfect transparency window the long-lived slow light can be achieved. In addition, we find that the conversion between the perfect OMIT and optomechanically induced absorption can be easily achieved just by adjusting the driving field strength of the second cavity. We believe that the results can be used to control optical transmission in modern optical networks.
Distributed quantum computation has gained extensive attention. In this paper, we consider a search problem that includes only one target item in the unordered database. After that, we propose a distributed exact Grover’s algorithm (DEGA), which decomposes the original search problem into
The phenomenal progress of quantum information theory over the last decade has substantially broadened the potential to simulate the superposition of states for exponential speedup of quantum algorithms over their classical peers. Therefore, the conventional and modern cryptographic standards (encryption and authentication) are susceptible to Shor’s and Grover’s algorithms on quantum computers. The significant improvement in technology permits consummate levels of data protection by encoding classical data into small quantum states that can only be utilized once by leveraging the capabilities of quantum-assisted classical computations. Considering the frequent data breaches and increasingly stringent privacy legislation, we introduce a hybrid quantum-classical model to transform classical data into unclonable states, and we experimentally demonstrate perfect state transfer to exemplify the classical data. To alleviate implementation complexity, we propose an arbitrary quantum signature scheme that does not require the establishment of entangled states to authenticate users in order to transmit and receive arbitrated states to retrieve classical data. The consequences of the probabilistic model indicate that the quantum-assisted classical framework substantially enhances the performance and security of digital data, and paves the way toward real-world applications.
The Su−Schrieffer−Heeger (SSH) model, commonly used for robust state transfers through topologically protected edge pumping, has been generalized and exploited to engineer diverse functional quantum devices. Here, we propose to realize a fast topological beam splitter based on a generalized SSH model by accelerating the quantum state transfer (QST) process essentially limited by adiabatic requirements. The scheme involves delicate orchestration of the instantaneous energy spectrum through exponential modulation of nearest neighbor coupling strengths and onsite energies, yielding a significantly accelerated beam splitting process. Due to properties of topological pumping and accelerated QST, the beam splitter exhibits strong robustness against parameter disorders and losses of system. In addition, the model demonstrates good scalability and can be extended to two-dimensional crossed-chain structures to realize a topological router with variable numbers of output ports. Our work provides practical prospects for fast and robust topological QST in feasible quantum devices in large-scale quantum information processing.
Uncertainty relation lies at the heart of quantum physics, which is one of the fundamental characteristics of quantum mechanics. With the advent of quantum information theory, entropic uncertainty relation was proposed, which plays an important and irreplaceable role in quantum information science. In this work, we attempt to observe dynamics of entropic uncertainty in the presence of quantum memory under two different types of Lee−Yang dephasing channels. It is interesting to find that the dephasing channels have a negative effect on decreasing the uncertainty and the analogous partition function is anti-correlated with the uncertainty. In addition, we here propose an effective strategy to manipulate the uncertainty of interest of the subsystem by performing a parity-time symmetric (
Quantum secure direct communication (QSDC) is a method of communication that transmits secret information directly through a quantum channel. This paper proposes a two-step QSDC scheme based on intermediate-basis, in which the intermediate-basis Einstein−Podolsky−Rosen (EPR) pairs can assist to detect channel security and help encode information. Specifically, the intermediate-basis EPR pairs reduce the probability of Eve choosing the correct measurement basis in the first step, enhancing the security of the system. Moreover, they encode information together with information EPR pairs to improve the transmission efficiency in the second step. We consider the security of the protocol under coherent attack when Eve takes different dimensions of the auxiliary system. The simulation results show that intermediate-basis EPR pairs can lower the upper limit of the amount of information that Eve can steal in both attack scenarios. Therefore, the proposed protocol can ensure that the legitimate parties get more confidential information and improve the transmission efficiency.