Parallel perception of visual motion using light-tunable memory matrix.

Parallel perception of visual motion is of crucial significance to the development of an intelligent machine vision system. However, implementing in-sensor parallel visual motion perception using conventional complementary metal-oxide semiconductor technology is challenging, because the temporal and spatial information embedded in motion cannot be simultaneously encoded and perceived at the sensory level. Here, we demonstrate the parallel perception of diverse motion modes at the sensor level by exploiting light-tunable memory matrix in a van der Waals (vdW) heterostructure array.

Cascadable in-memory computing based on symmetric writing and readout.

The building block of in-memory computing with spintronic devices is mainly based on the magnetic tunnel junction with perpendicular interfacial anisotropy (p-MTJ). The resulting asymmetric write and readout operations impose challenges in downscaling and direct cascadability of p-MTJ devices. Here, we propose that a previously unimplemented symmetric write and readout mechanism can be realized in perpendicular-anisotropy spin-orbit (PASO) quantum materials based on FeGeTe and WTe.

Approaching the Intrinsic Threshold Breakdown Voltage and Ultrahigh Gain in a Graphite/InSe Schottky Photodetector.

Realizing both ultralow breakdown voltage and ultrahigh gain is one of the major challenges in the development of high-performance avalanche photodetector. Here, it is reported that an ultrahigh avalanche gain of 3 × 10 can be realized in the graphite/InSe Schottky photodetector at a breakdown voltage down to 5.5 V.

Tunable quantum criticalities in an isospin extended Hubbard model simulator.

Studying strong electron correlations has been an essential driving force for pushing the frontiers of condensed matter physics. In particular, in the vicinity of correlation-driven quantum phase transitions (QPTs), quantum critical fluctuations of multiple degrees of freedom facilitate exotic many-body states and quantum critical behaviours beyond Landau's framework. Recently, moiré heterostructures of van der Waals materials have been demonstrated as highly tunable quantum platforms for exploring fascinating, strongly correlated quantum physics.

Nonvolatile van der Waals Heterostructure Phototransistor for Encrypted Optoelectronic Logic Circuit.

With the rising demand for information security, there has been a surge of interest in harnessing the intrinsic physical properties of device for designing a secure logic circuit. Here we provide an innovative approach to realize the secure optoelectronic logic circuit based on nonvolatile van der Waals (vdW) heterostructure phototransistors. The phototransistors comprising WSe and h-BN flakes exhibit electrical tunability of nonvolatile conductance under cooperative operations of electrical and light stimulus.

Scalable massively parallel computing using continuous-time data representation in nanoscale crossbar array.

The growth of connected intelligent devices in the Internet of Things has created a pressing need for real-time processing and understanding of large volumes of analogue data. The difficulty in boosting the computing speed renders digital computing unable to meet the demand for processing analogue information that is intrinsically continuous in magnitude and time. By utilizing a continuous data representation in a nanoscale crossbar array, parallel computing can be implemented for the direct processing of analogue information in real time.

Observation of Negative Terahertz Photoconductivity in Large Area Type-II Dirac Semimetal PtTe_{2}.

As a newly emergent type-II Dirac semimetal, platinum telluride (PtTe_{2}) stands out from other two dimensional noble-transition-metal dichalcogenides for the unique band structure and novel physical properties, and has been studied extensively. However, the ultrafast response of low energy quasiparticle excitation in terahertz frequency remains nearly unexplored yet. Herein, we employ optical pump-terahertz probe (OPTP) spectroscopy to systematically study the photocarrier dynamics of PtTe_{2} thin films with varying pump fluence, temperature, and film thickness.

Strain-Sensitive Magnetization Reversal of a van der Waals Magnet.

By virtue of the layered structure, van der Waals (vdW) magnets are sensitive to the lattice deformation controlled by the external strain, providing an ideal platform to explore the one-step magnetization reversal that is still conceptual in conventional magnets due to the limited strain-tuning range of the coercive field. In this study, a uniaxial tensile strain is applied to thin flakes of the vdW magnet Fe GeTe (FGT), and a dramatic increase of the coercive field (H ) by more than 150% with an applied strain of 0.32% is observed.

Networking retinomorphic sensor with memristive crossbar for brain-inspired visual perception.

Compared to human vision, conventional machine vision composed of an image sensor and processor suffers from high latency and large power consumption due to physically separated image sensing and processing. A neuromorphic vision system with brain-inspired visual perception provides a promising solution to the problem. Here we propose and demonstrate a prototype neuromorphic vision system by networking a retinomorphic sensor with a memristive crossbar.

Tuning Electrical Conductance in Bilayer MoS through Defect-Mediated Interlayer Chemical Bonding.

Interlayer interaction could substantially affect the electrical transport in transition metal dichalcogenides, serving as an effective way to control the device performance. However, it is still challenging to utilize interlayer interaction in weakly interlayer-coupled materials such as pristine MoS to realize layer-dependent tunable transport behavior. Here, we demonstrate that, by substitutional doping of vanadium atoms in the Mo sites of the MoS lattice, the vanadium-doped monolayer MoS device exhibits an ambipolar field effect characteristic, while its bilayer device demonstrates a heavy -type field effect feature, in sharp contrast to the pristine monolayer and bilayer MoS devices, both of which show similar -type electrical transport behaviors.

Gate-tunable van der Waals heterostructure for reconfigurable neural network vision sensor.

Early processing of visual information takes place in the human retina. Mimicking neurobiological structures and functionalities of the retina provides a promising pathway to achieving vision sensor with highly efficient image processing. Here, we demonstrate a prototype vision sensor that operates via the gate-tunable positive and negative photoresponses of the van der Waals (vdW) vertical heterostructures.

Robust Impact-Ionization Field-Effect Transistor Based on Nanoscale Vertical Graphene/Black Phosphorus/Indium Selenide Heterostructures.

Maintaining the rapid development of information technology by scaling down a metal-oxide semiconductor field-effect transistor faces two serious challenges. First, the gate field loses control of the channel as it continuously decreases. Second, the fundamental thermionic limit restricts the reduction in supply voltage.

Edge-Epitaxial Growth of InSe Nanowires toward High-Performance Photodetectors.

Semiconducting nanowires offer many opportunities for electronic and optoelectronic device applications due to their unique geometries and physical properties. However, it is challenging to synthesize semiconducting nanowires directly on a SiO /Si substrate due to lattice mismatch. Here, a catalysis-free approach is developed to achieve direct synthesis of long and straight InSe nanowires on SiO /Si substrates through edge-homoepitaxial growth.

Van der Waals Heterostructures for High-Performance Device Applications: Challenges and Opportunities.

The discovery of two-dimensional (2D) materials with unique electronic, superior optoelectronic, or intrinsic magnetic order has triggered worldwide interest in the fields of material science, condensed matter physics, and device physics. Vertically stacking 2D materials with distinct electronic and optical as well as magnetic properties enables the creation of a large variety of van der Waals heterostructures. The diverse properties of the vertical heterostructures open unprecedented opportunities for various kinds of device applications, e.

Direct Evidence for Charge Compensation-Induced Large Magnetoresistance in Thin WTe.

Since the discovery of extremely large nonsaturating magnetoresistance (MR) in WTe, much effort has been devoted to understanding the underlying mechanism, which is still under debate. Here, we explicitly identify the dominant physical origin of the large nonsaturating MR through in situ tuning of the magneto-transport properties in thin WTe film. With an electrostatic doping approach, we observed a nonmonotonic gate dependence of the MR.

Experimental Identification of Critical Condition for Drastically Enhancing Thermoelectric Power Factor of Two-Dimensional Layered Materials.

Nanostructuring is an extremely promising path to high-performance thermoelectrics. Favorable improvements in thermal conductivity are attainable in many material systems, and theoretical work points to large improvements in electronic properties. However, realization of the electronic benefits in practical materials has been elusive experimentally.

Proximity-Induced Superconductivity with Subgap Anomaly in Type II Weyl Semi-Metal WTe.

Due to the nontrivial topological band structure in type II Weyl semi-metal tungsten ditelluride (WTe), unconventional properties may emerge in its superconducting phase. While realizing intrinsic superconductivity has been challenging in the type II Weyl semi-metal WTe, the proximity effect may open an avenue for the realization of superconductivity. Here, we report the observation of proximity-induced superconductivity with a long coherence length along the c axis in WTe thin flakes based on a WTe/NbSe van der Waals heterostructure.

Negative Photoconductance in van der Waals Heterostructure-Based Floating Gate Phototransistor.

van der Waals (vdW) heterostructures made of two-dimensional materials have been demonstrated to be versatile architectures for optoelectronic applications due to strong light--matter interactions. However, most light-controlled phenomena and applications in the vdW heterostructures rely on positive photoconductance (PPC). Negative photoconductance (NPC) has not yet been reported in vdW heterostructures.

Gate-Induced Interfacial Superconductivity in 1T-SnSe.

Layered metal chalcogenide materials provide a versatile platform to investigate emergent phenomena and two-dimensional (2D) superconductivity at/near the atomically thin limit. In particular, gate-induced interfacial superconductivity realized by the use of an electric-double-layer transistor (EDLT) has greatly extended the capability to electrically induce superconductivity in oxides, nitrides, and transition metal chalcogenides and enable one to explore new physics, such as the Ising pairing mechanism. Exploiting gate-induced superconductivity in various materials can provide us with additional platforms to understand emergent interfacial superconductivity.