The van der Waals (vdW) heterostructure, made up of two dissimilar two-dimensional materials held together by van der Waals interactions, has excellent electronic and optoelectronic properties as it provides a superior interface quality without the lattice mismatch problem. Here, we report the development and photoresponse characteristics of a p-n diode based on a stacked black phosphorus (BP) and rhenium disulfide (ReS2) heterojunction. The heterojunction showed a clear gate-tunable rectifying behavior similar to that of the conventional p-n junction diode. Under UV illumination, the BP/ReS2 p-n diode displayed a high photoresponsivity of 4120 A W-1 and we were able to modify the photoresponse properties by adjusting the back gate voltage. Moreover, an investigation of various channel lengths yielded the highest photoresponsivity of 11 811 A W-1 for a BP length of 1 μm. These results suggested vdW 2D materials to be promising for developing advanced heterojunction devices for nano-optoelectronics.

We use ionic liquid-assisted electric field effect to tune the carrier density in an electron-doped cuprate ultrathin film and cause a two-dimensional superconductor-insulator transition (SIT). The low upper critical field in this system allows us to perform magnetic field (B)-induced SIT in the liquid-gated superconducting film. Finite-size scaling analysis indicates that SITs induced both by electric and magnetic field are quantum phase transitions and the transitions are governed by percolation effects -quantum mechanical in the former and classical in the latter case. Compared to the hole-doped cuprates, the SITs in electron-doped system occur at critical sheet resistances (R c ) much lower than the pair quantum resistance R Q =h/(2e) 2 =6.45 kΩ, suggesting the possible existence of fermionic excitations at finite temperature at the insulating phase near SITs. Two-dimensional superconductor-insulator quantum phase transitions in an electron-doped cuprate Supplemental Material

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Graphene, transition metal-dichalcogenides (TMDs), and black phosphorus (BP) are widely exploited as building blocks for such vdWs heterostructure due to their unique electrical and optical properties. [8][9][10][11][12][13] Among these 2D materials, BP has attracted extensive attention because of its high carrier mobility (up to 1000 cm 2 V −1 s −1 at room temperature), moderate tunable direct bandgap on thickness (from 0.3 eV for bulk to 2.0 eV for monolayer), and intrinsic anisotropy arising from the puckered structure. [14][15][16][17] In the past years, a host of BP-based vdWs heterostructures such as graphene/ BP, TMDs/BP, and h-BN/BP architecture, have been fabricated to explore their electronic and photoelectric properties, which have shown promising applications for fieldeffect transistors (FETs), [18][19][20] photodetectors, [8,21,22] flexible devices, [23] memory device, [24] logic circuits, [25] and so on. In the most studied BP/MoS 2 heterostructure, [11,20,25] diverse diode characteristics, including back forward rectifying diode, Zener diode, and forward rectifying diode, have been obtained by BP thickness modulation. [20] A tunable multivalued logic performance was also realized in such heterostructure, providing a step forward toward the future logic applications. [25] Recently, tin-based dichalcogenide SnSe x S 1−x , [26][27][28][29][30][31][32] a layered semiconductor family with environmental friendly and low cost characteristics, has been explored for nanoelectronic applications. In addition, the wide bandgap ranging from ≈1 to ≈2.1 eV opens the possibility of developing versatile devices by band engineering. In this work, we present a realization of BP/SnSeS heterostructure and explore its carrier transport and logic characteristics for the first time. The heterostructure based on Te-doped BP exhibits high carrier mobility and an exceptional ambient stability. [33] Diverse diode characteristics are observed with the modulation of band alignment at BP/SnSeS interface. Furthermore, we demonstrated a multivalued logic state by varying BP length, suggesting that BP/SnSeS heterostructure has promising application in low-power multivalued logic circuits.The schematic of the proposed BP/SnSeS heterostructure is shown in Figure 1a. Both BP and SnSeS flakes were mechanically exfoliated from their bulk crystals. Using a dry transfer technique, the BP flake was first transferred onto the HfO 2 (30 nm)/ Si substrate with prepared electrical pads, and then exfoliated SnSeS flake was artificially stacked atop the BP flake forming BP/SnSeS heterostructure. After that, multiple metal electrodes were fabricated on the top of BP and SnSeS regions by van der Waals (vdW) heterostructures have attracted intensive attention due to their great potential in future functional electronic and optoelectronic devices. Here, a systematic electrical transport investigation on black phosphorus (BP)/SnSeS heterostructures is presented. The BP/SnSeS heterostructure shows diverse diode functional features by modulating BP cha...

In recent years, low-dimensional materials have received extensive attention in the field of electronics and optoelectronics. Among them, photoelectric devices based on photoconductive effect in low-dimensional materials have a broad development space. In contrast to positive photoconductivity, negative photoconductivity (NPC) refers to a phenomenon that the conductivity decreases under illumination. It has novel application prospects in the field of optoelectronics, memory, and gas detection, etc. In this paper, we review reports about the NPC effect in low-dimensional materials and systematically summarize the mechanisms to form the NPC effect in existing low-dimensional materials.

We report on the sparse neuromorphic computing based on spin-torque diodes (STDs). The rectification characteristics of STDs have been investigated in the absence and presence of d.c. bias currents. While the injection locking phenomenon is observed in our devices, the output functions versus the d.c. bias currents mimic artificial neurons with sparse representations. Furthermore, we construct a neural network with STD neurons to recognize the handwritten digits in the Mixed National Institute of Standards and Technology database, with a produced accuracy of up to 92.7%. The results suggest that STDs have potential to be building blocks for the realization of a biologically plausible neuromorphic computing system.

The recent discovery of magnetic two-dimensional (2D) crystals offers a platform to study the spin-related phenomena in van der Waals (vdW) heterostructures. Here, we investigate the anomalous Hall effect in the bilayer all-vdW heterostructure of Fe3GeTe2 (FGT)/WTe2. In such devices, the coercivity of thin-FGT flakes can be effectively modulated by the current, which is mainly attributed to the Joule heating effect generated at the interface of the FGT/WTe2 bilayer because of the low interfacial thermal conductance. The gradient ΔHc/ΔJFGT is as large as 0.55 kOe MA−1 cm2 at 10 K. Our work provides great guidance for the design of next generation spintronic devices based on atomically thin van der Waals heterostructures.

Integrating multiple properties in a single system is crucial for the continuous developments in electronic devices. However, some physical properties are mutually exclusive in nature. Here, we report the coexistence of two seemingly mutually exclusive properties-polarity and two-dimensional conductivity-in ferroelectric Ba 0.2 Sr 0.8 TiO 3 thin films at the LaAlO 3 / Ba 0.2 Sr 0.8 TiO 3 interface at room temperature. The polarity of a ∼3.2 nm Ba 0.2 Sr 0.8 TiO 3 thin film is preserved with a two-dimensional mobile carrier density of ∼0.05 electron per unit cell. We show that the electronic reconstruction resulting from the competition between the built-in electric field of LaAlO 3 and the polarization of Ba 0.2 Sr 0.8 TiO 3 is responsible for this unusual two-dimensional conducting polar phase. The general concept of exploiting mutually exclusive properties at oxide interfaces via electronic reconstruction may be applicable to other strongly-correlated oxide interfaces, thus opening windows to new functional nanoscale materials for applications in novel nanoelectronics.