双量子环的隧穿电导和隧穿磁电阻

研究了双量子环的隧穿电导和隧穿磁电阻,研究结果表明:隧穿电导和隧穿磁电阻都随半导体环增大做周期性等幅振荡。δ势垒、Rashba自旋轨道耦合、AB磁通对隧穿电导或隧穿磁电阻的影响各不相同。隧穿磁电阻随AB磁通增强发生周期性等幅振荡,并随φ0角的减小而增大。两电极磁矩方向反平行时,隧穿磁电阻恒为零。     

Revealing Controllable Anisotropic Magnetoresistance in Spin–Orbit Coupled Antiferromagnet Sr2IrO4

Antiferromagnetic spintronics actively introduces new principles of magnetic memory, in which the most fundamental spin‐dependent phenomena, i.e., anisotropic magnetoresistance effects, are governed by an antiferromagnet instead of a ferromagnet. A general scenario of the antiferromagnetic anisotropic magnetoresistance effects mainly stems from the magnetocrystalline anisotropy related to spin–orbit coupling. Here magnetic field driven contour rotation of the fourfold anisotropic magnetoresistance in bare antiferromagnetic Sr₂IrO₄/SrTiO₃ (001) thin films hosting a strong spin–orbit coupling induced J_eff = 1/2 Mott state is demonstrated. Concurrently, an intriguing minimal in the magnetoresistance emerges. Through first principles calculations, the bandgap engineering due to rotation of the Ir isospins is revealed to be responsible for these emergent phenomena, different from the traditional scenario where relatively more conductive state is obtained usually when magnetic field is applied along the magnetic easy axis. These findings demonstrate a new efficient route, i.e., via the novel J_eff = 1/2 state, to realize controllable anisotropic magnetoresistance in antiferromagnetic materials.     

Silicon‐Based Current‐Controlled Reconfigurable Magnetoresistance Logic Combined with Non‐Volatile Memory

Silicon‐based complementary metal‐oxide‐semiconductor (CMOS) transistors have achieved great success. However, the traditional development pathway is approaching its fundamental limits. Magnetoelectronics logic, especially magnetic‐field‐based logic, shows promise for surpassing the development limits of CMOS logic and arouses profound attentions. Existing proposals of magnetic‐field‐based logic are based on exotic semiconductors and difficult for further technological implementation. Here, a kind of diode‐assisted geometry‐enhanced low‐magnetic‐field magnetoresistance (MR) mechanism is proposed. It couples p‐n junction's nonlinear transport characteristic and Lorentz force by geometry, and shows extremely large low‐magnetic‐field MR (>120% at 0.15 T). Further, it is applied to experimentally demonstrate current‐controlled reconfigurable magnetoresistance logic on the silicon platform at room temperature. This logic device could perform all four basic Boolean logic including AND, OR, NAND and NOR in one device. Combined with non‐volatile magnetic memory, this logic architecture with unique magnetoelectric properties has the advantages of current‐controlled reconfiguration, zero refresh consumption, instant‐on performance and would bridge the processor‐memory gap. Our findings would pave the way in silicon‐based magnetoelectronics and offer a route to make a new kind of microprocessor with potential of high performance.     

栅控电势磁性隧道结的隧穿磁阻研究

基于Slonczewski理论模型和矩阵方法研究了由栅控制中间层电势高度的磁性隧道结的隧穿磁阻效应。数值计算了中间层势垒为0~3 V以及中间层势阱为0~3 V的磁性隧道结的隧穿磁阻随着中间层厚度改变的变化曲线。计算结果表明,当中间层为势垒时,隧穿磁阻随着中间层厚度单调下降;当中间层为势阱时,隧穿磁阻随着中间层厚度振荡,并且相比于势垒情况时明显提高。这说明栅控中间层磁性隧道结相比于传统磁性隧道结具有更好的可控性和提高隧穿磁阻效应的潜力。     

Single‐Electron Tunneling through Molecular Quantum Dots in a Metal‐Insulator‐Semiconductor Structure

A sigle‐electron tunneling (SET) in a metal‐insulator‐semiconductor (MIS) structure is demonstrated, in which C₆₀ and copper phthalocyanine (CuPc) molecules are embedded as quantum dots in the insulator layer. The SET is found to originate from resonant tunneling via the energy levels of the embedded molecules, (e.g., the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO)). These findings show that the threshold voltages for SET are tunable according to the energy levels of the molecules. Furthermore, SET is observable even near room temperature. The results suggest, together with the fact that these properties are demonstrated in a practical device configuration, that the integration of molecular dots into the Si‐MIS structure has considerable potential for achieving novel SET devices. Moreover, the attempt allows large‐scale integration of individual molecular functionalities.     

Anomalous Anisotropic Magnetoresistance of Antiferromagnetic Epitaxial Bimetallic Films: Mn2Au and Mn2Au/Fe Bilayers

Recently intensive efforts have been devoted to the emerging field of antiferromagnetic (AFM) spintronics, where ferromagnetic electrodes are substituted by antiferromagnets. This study investigates the anisotropic magnetoresistance (AMR) of epitaxial tetragonal antiferromagnetic bimetallic films: Mn₂Au and Mn₂Au/Fe bilayers. An anomalous AMR effect with additional peaks is observed. This study theoretically and experimentally demonstrates that the AFM spins of Mn₂Au can be viewed and controlled at room temperature, and this is achievable with a notably relatively small magnetic field of 200 mT. Strong hybridization between Au and Mn, and strong modification of the intrinsic quadratic anisotropy of Mn₂Au from interfacial biquadratic anisotropy result in an additional anomalous AMR component of 1%. The findings suggest that Mn₂Au films can be used in room temperature antiferromagnetic spintronics.     

A Time‐Optimal Anti‐collision Algorithm for FSA‐Based RFID Systems

With the introduction of the new generation RFID technology, EPCglobal Class‐1 Generation‐2, there is considerable interest in improving the performance of the framed slotted Aloha (FSA)‐based tag collision arbitration protocol. We suggest a novel time‐optimal anti‐collision algorithm for the FSA protocol. Our performance evaluation demonstrates that our algorithm outperforms other tag collision arbitration schemes.     

Spin‐Structured Multilayers: A New Class of Materials for Precision Spintronics

Magnetoelectronic multilayer devices are widely used in today's information and sensor technology. Their functionality, however, is limited by the inherent properties of magnetic exchange or dipolar coupling which constrain possible spin configurations to collinear or perpendicular alignments of adjacent layers. Here, a deposition procedure is introduced that allows for a new class of layered materials in which complex spin structures can be accurately designed to result in a multitude of new and precisely adjustable spintronic and magnetoresistive properties. The magnetization direction and coercivity of each individual layer are determined by the deposition process in oblique incidence geometry and can be completely decoupled from neighboring layers. This applies for layers of any ferromagnetic material down to layer thicknesses of a few nm and lateral dimensions of a few 100 nm, enabling the design of efficient and compact magnetoelectronic devices, encompassing precision magnetoresistive sensors as well as layer systems with multiple addressable remanent states for magnetic memory applications.     

Gen2‐Based Tag Anti‐collision Algorithms Using Chebyshev's Inequality and Adjustable Frame Size

Arbitration of tag collision is a significant issue for fast tag identification in RFID systems. A good tag anti‐collision algorithm can reduce collisions and increase the efficiency of tag identification. EPCglobal Generation‐2 (Gen2) for passive RFID systems uses probabilistic slotted ALOHA with a Q algorithm, which is a kind of dynamic framed slotted ALOHA (DFSA), as the tag anti‐collision algorithm. In this paper, we analyze the performance of the Q algorithm used in Gen2, and analyze the methods for estimating the number of slots and tags for DFSA. To increase the efficiency of tag identification, we propose new tag anti‐collision algorithms, namely, Chebyshev's inequality, fixed adjustable framed Q, adaptive adjustable framed Q, and hybrid Q. The simulation results show that all the proposed algorithms outperform the conventional Q algorithm used in Gen2. Of all the proposed algorithms, AAFQ provides the best performance in terms of identification time and collision ratio and maximizes throughput and system efficiency. However, there is a tradeoff of complexity and performance between the CHI and AAFQ algorithms.     

Atomic‐Scale Manipulation and In Situ Characterization with Scanning Tunneling Microscopy

Scanning tunneling microscope (STM) has presented a revolutionary methodology to nanoscience and nanotechnology. It enables imaging of the topography of surfaces, mapping the distribution of electronic density of states, and manipulating individual atoms and molecules, all at atomic resolutions. In particular, atom manipulation capability has evolved from fabricating individual nanostructures toward the scalable production of the atomic‐sized devices bottom‐up. The combination of precision synthesis and in situ characterization has enabled direct visualization of many quantum phenomena and fast proof‐of‐principle testing of quantum device functions with immediate feedback to guide improved synthesis. Several representative examples are reviewed to demonstrate the recent development of atomic‐scale manipulation, focusing on progress that addresses quantum properties by design in several technologically relevant materials systems. Integration of several atomically precisely controlled probes in a multiprobe STM system vastly extends the capability of in situ characterization to a new dimension where the charge and spin transport behaviors can be examined from mesoscopic to atomic length scale. The automation of atomic‐scale manipulation and the integration with well‐established lithographic processes further push this bottom‐up approach to a new level that combines reproducible fabrication, extraordinary programmability, and the ability to produce large‐scale arrays of quantum structures.     

Enhanced Omnidirectional Photovoltaic Performance of Solar Cells Using Multiple‐Discrete‐Layer Tailored‐ and Low‐Refractive Index Anti‐Reflection Coatings

An optimized four‐layer tailored‐ and low‐refractive index anti‐reflection (AR) coating on an inverted metamorphic (IMM) triple‐junction solar cell device is demonstrated. Due to an excellent refractive index matching with the ambient air by using tailored‐ and low‐refractive index nanoporous SiO₂ layers and owing to a multiple‐discrete‐layer design of the AR coating optimized by a genetic algorithm, such a four‐layer AR coating shows excellent broadband and omnidirectional AR characteristics and significantly enhances the omnidirectional photovoltaic performance of IMM solar cell devices. Comparing the photovoltaic performance of an IMM solar cell device with the four‐layer AR coating and an IMM solar cell with the conventional SiO₂/TiO₂ double layer AR coating, the four‐layer AR coating achieves an angle‐of‐incidence (AOI) averaged short‐circuit current density, J_SC, enhancement of 34.4%, whereas the conventional double layer AR coating only achieves an AOI‐averaged J_SC enhancement of 25.3%. The measured reflectance reduction and omnidirectional photovoltaic performance enhancement of the four‐layer AR coating are to our knowledge, the largest ever reported in the literature of solar cell devices.     

Temporal Anti‐aliasing of a Stereoscopic 3D Video

Frequency domain analysis is a fundamental procedure for understanding the characteristics of visual data. Several studies have been conducted with 2D videos, but analysis of stereoscopic 3D videos is rarely carried out. In this paper, we derive the Fourier transform of a simplified 3D video signal and analyze how a 3D video is influenced by disparity and motion in terms of temporal aliasing. It is already known that object motion affects temporal frequency characteristics of a time‐varying image sequence. In our analysis, we show that a 3D video is influenced not only by motion but also by disparity. Based on this conclusion, we present a temporal anti‐aliasing filter for a 3D video. Since the human process of depth perception mainly determines the quality of a reproduced 3D image, 2D image processing techniques are not directly applicable to 3D images. The analysis presented in this paper will be useful for reducing undesirable visual artifacts in 3D video as well as for assisting the development of relevant technologies.     

Conception and Performance Analysis of Efficient CDMA‐Based Full‐Duplex Anti‐collision Scheme

Ultra‐high‐frequency radio‐frequency identification (UHF RFID) is widely applied in different industries. The Frame Slotted ALOHA in EPC C1G2 suffers severe collisions that limit the efficiency of tag recognition. An efficient full‐duplex anti‐collision scheme is proposed to reduce the rate of collision by coordinating the transmitting process of CDMA UWB uplink and UHF downlink. The relevant mathematical models are built to analyze the performance of the proposed scheme. Through simulation, some important findings are gained. The maximum number of identified tags in one slot is g/e (g is the number of PN codes and e is Euler's constant) when the number of tags is equal to mg (m is the number of slots). Unlike the Frame Slotted ALOHA, even if the frame size is small and the number of tags is large, there aren't too many collisions if the number of PN codes is large enough. Our approach with 7‐bit Gold codes, 15‐bit Gold codes, or 31‐bit Gold codes operates 1.4 times, 1.7 times, or 3 times faster than the CDMA Slotted ALOHA, respectively, and 14.5 times, 16.2 times, or 18.5 times faster than the EPC C1 G2 system, respectively. More than 2,000 tags can be processed within 300 ms in our approach.     

Large Tunnel Magnetoresistance in Epitaxial Oxide Spin‐Filter Tunnel Junctions

A high‐performance spin filter tunnel junction composed of an epitaxial oxide heterostructure is reported. By independently controlling the magnetic orientations of ferromagnetic tunnel barrier and electrode layers, a tunnel magnetoresistance ratio exceeding 120% is obtained purely by the spin filtering effect. A newly introduced spin filter material, Pr_0.8Ca_0.2Mn_1‐yCo_yO₃, is shown to be useful for building novel multibarrier spintronic tunnel devices due to its composition‐controlled magnetic hardness.     

Tuning a Binary Ferromagnet into a Multistate Synapse with Spin–Orbit‐Torque‐Induced Plasticity

Ferromagnets with binary states are limited for applications as artificial synapses for neuromorphic computing. Here, it is shown how synaptic plasticity of a perpendicular ferromagnetic layer (FM1) can be obtained when it is interlayer exchange‐coupled by another in‐plane ferromagnetic layer (FM2), where a magnetic field‐free current‐driven multistate magnetization switching of FM1 in the Pt/FM1/Ta/FM2 structure is induced by spin–orbit torque. Current pulses are used to set the perpendicular magnetization state, which acts as the synapse weight, and spintronic implementation of the excitatory/inhibitory postsynaptic potentials and spike timing‐dependent plasticity are demonstrated. This functionality is made possible by the action of the in‐plane interlayer exchange coupling field which leads to broadened, multistate magnetic reversal characteristics. Numerical simulations, combined with investigations of a reference sample with a single perpendicular magnetized Pt/FM1/Ta structure, reveal that the broadening is due to the in‐plane field component tuning the efficiency of the spin–orbit torque to drive domain walls across a landscape of varying pinning potentials. The conventionally binary FM1 inside the Pt/FM1/Ta/FM2 structure with an inherent in‐plane coupling field is therefore tuned into a multistate perpendicular ferromagnet and represents a synaptic emulator for neuromorphic computing, demonstrating a significant pathway toward a combination of spintronics and synaptic electronics.     

Interface‐Assisted Sign Inversion of Magnetoresistance in Spin Valves Based on Novel Lanthanide Quinoline Molecules

Molecules are proposed to be an efficient medium to host spin‐polarized carriers, due to their weak spin relaxation mechanisms. While relatively long spin lifetimes are measured in molecular devices, the most promising route toward device functionalization is to use the chemical versatility of molecules to achieve a deterministic control and manipulation of the electron spin. Here, by combining magnetotransport experiments with element‐specific X‐ray absorption spectroscopy, this study shows the ability of molecules to modify spin‐dependent properties at the interface level via metal–molecule hybridization pathways. In particular, it is described how the formation of hybrid states determines the spin polarization at the relevant spin valve interfaces, allowing the control of macroscopic device parameters such as the sign and magnitude of the magnetoresistance. These results consolidate the application of the spinterface concept in a fully functional device platform.     

A Large Magnetoresistance Effect in p–n Junction Devices by the Space‐Charge Effect

The finding of an extremely large magnetoresistance effect on silicon based p–n junction with vertical geometry over a wide range of temperatures and magnetic fields is reported. A 2500% magnetoresistance ratio of the Si p–n junction is observed at room temperature with a magnetic field of 5 T and the applied bias voltage of only 6 V, while a magnetoresistance ratio of 25 000% is achieved at 100 K. The current‐voltage (I–V) behaviors under various external magnetic fields obey an exponential relationship, and the magnetoresistance effect is significantly enhanced by both contributions of the electric field inhomogeneity and carrier concentrations variation. Theoretical analysis using classical p–n junction transport equation is adapted to describe the I–V curves of the p–n junction at different magnetic fields and reveals that the large magnetoresistance effect origins from a change of space‐charge region in the p–n junction induced by external magnetic field. The results indicate that the conventional p–n junction is proposed to be used as a multifunctional material based on the interplay between electronic and magnetic response, which is significant for future magneto‐electronics in the semiconductor industry.     

A Biomimetic Mussel‐Inspired ε‐Poly‐l‐lysine Hydrogel with Robust Tissue‐Anchor and Anti‐Infection Capacity

In situ hydrogels have attracted considerable attention in tissue engineering because of their minimal invasiveness and ability to match the irregular tissue defects. However, hydrous physiological environments and the high level of moisture in hydrogels severely hamper binding to the target tissue and easily cause wound infection, thereby limiting the effectiveness in wound care management. Thus, forming an intimate assembly of the hydrogel to the tissue and preventing wound infecting still remains a significant challenge. In this study, inspired by mussel adhesive protein, a biomimetic dopamine‐modified ε‐poly‐l ‐lysine‐polyethylene glycol‐based hydrogel (PPD hydrogel) wound dressing is developed in situ using horseradish peroxidase cross‐linking. The biomimetic catechol–Lys residue distribution in PPD polymer provides a catechol–Lys cooperation effect, which endows the PPD hydrogels with superior wet tissue adhesion properties. It is demonstrated that the PPD hydrogel can facilely and intimately integrate with biological tissue and exhibits superior capacity of in vivo hemostatic and accelerated wound repair. In addition, the hydrogels exhibit outstanding anti‐infection property because of the inherent antibacterial ability of ε‐poly‐l ‐lysine. These findings shed new light on the development of mussel‐inspired tissue‐anchored and antibacterial hydrogel materials serving as wound dressings.     

Interlayer Band‐to‐Band Tunneling and Negative Differential Resistance in van der Waals BP/InSe Field‐Effect Transistors

Atomically thin layers of van der Waals (vdW) crystals offer an ideal material platform to realize tunnel field‐effect transistors (TFETs) that exploit the tunneling of charge carriers across the forbidden gap of a vdW heterojunction. This type of device requires a precise energy band alignment of the different layers of the junction to optimize the tunnel current. Among 2D vdW materials, black phosphorus (BP) and indium selenide (InSe) have a Brillouin zone‐centered conduction and valence bands, and a type II band offset, both ideally suited for band‐to‐band tunneling. TFETs based on BP/InSe heterojunctions with diverse electrical transport characteristics are demonstrated: forward rectifying, Zener tunneling, and backward rectifying characteristics are realized in BP/InSe junctions with different thickness of the BP layer or by electrostatic gating of the junction. Electrostatic gating yields a large on/off current ratio of up to 10⁸ and negative differential resistance at low applied voltages (V ≈ 0.2 V). These findings illustrate versatile functionalities of TFETs based on BP and InSe, offering opportunities for applications of these 2D materials beyond the device architectures reported in the current literature.     

Combination of Bacterial‐Photothermal Therapy with an Anti‐PD‐1 Peptide Depot for Enhanced Immunity against Advanced Cancer

Photothermal therapy (PTT) is a promising cancer treatment, but it has so far proven successful only with relatively small subcutaneous tumors in animal models. Treating larger tumors (≈200 mm³) is challenging because most PTT materials do not efficiently reach the hypoxic, avascular center of tumors, and the immunosuppressive tumor microenvironment prevents T cells from fighting against residual tumor cells, thereby allowing recurrence and metastasis. Here, the widely used PTT material polydopamine is coated on the surface of the facultative anaerobe Salmonella VNP20009, which can penetrate deep into larger tumors. The coated bacteria are intravenously injected followed by near‐infrared laser irradiation at the tumor site, combined with a local inoculation of phospholipid‐based phase separation gel containing the anti‐programmed cell death‐1 peptide AUNP‐12. The gel releases AUNP‐12 sustainably during 42 days, maintaining the tumor microenvironment as immunopermissive. Using a mouse model of melanoma, this triple combination of biotherapy, PTT, and sustainable programmed cell death‐1 (PD‐1) blockade shows high efficiency on eliciting robust antitumor immune responses and eliminating relatively large tumors in 50% of animals within 80 days. Thus, the results shed new light on a previously unrecognized immunological facet of bacteria‐mediated therapy, and this innovative triple therapy may be a powerful cancer immunotherapy tool.