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The interplay between strong Coulomb interactions and kinetic energy leads to intricate many-body competing ground states owing to quantum fluctuations in 2D electron and hole gases. However, the simultaneous observation of quantum critical phenomena in both electron and hole regimes remains elusive. Here, we utilize anisotropic black phosphorus (BP) to show density-driven metal–insulator transition with a critical conductance ~e2/hwhich highlights the significant role of quantum fluctuations in both hole and electron regimes. We observe a T-linear resistivity from the deep metallic phase to the metal–insulator boundary at moderate temperatures, while it turns to Fermi liquid behavior in the deep metallic phase at low temperatures in both regimes. An analysis of the resistivity suggests that disorder-dominated transport leads to T-linear behavior in the hole regime, while in the electron regime, the T-linear resistivity results from strong Coulomb interactions, suggestive of strange-metal behavior. Successful scaling collapse of the resistivity in the T-linear region demonstrates the link between quantum criticality and the T-linear resistivity in both regimes. Our study provides compelling evidence that ambipolar BP could serve as an exciting testbed for investigating exotic states and quantum critical phenomena in hole and electron regimes of 2D semiconductors.

We present a joint theoretical and experimental investigation on the origin of ferromagnetism in Mn-doped ZnO. Theoretical calculations revealed that the zinc vacancy (VZn) induces ferromagnetic ordering (FMO), whereas the oxygen vacancy (VO) quenches FMO in the Mn-doped ZnO system. This is further corroborated by the experimental results. Magnetic measurements revealed that Mn-doped ZnO shows room-temperature ferromagnetism (RTFM). Saturated magnetic moment per Mn2+ion increases with oxygen partial pressure, indicating that the VZnenhances FMO in Mn-doped ZnO. Electron paramagnetic resonance and photoluminescence measurements revealed the presence of VZnin Mn-doped ZnO films. X-ray photoelectron spectroscopy measurements showed mixed oxidation states of Mn in Mn-doped ZnO films. Finally, we show that RTFM at very low doping concentrations is due to the overlapping of bound magnetic polarons. However, due to antiferromagnetic coupling at higher doping concentrations, the FMO weakens.

Recently, multivalued logic (MVL) circuits have attracted tremendous interest due to their ability to process more data by increasing the number of logic states rather than the integration density. Here, we fabricate logic circuits based on molybdenum telluride (MoTe2)/black phosphorus (BP) van der Waals heterojunctions with different structural phases of MoTe2. Owing to the different electrical properties of the 2H and mixed 2H +1T′ phases of MoTe2, tunable logic devices have been realized. A logic circuit based on a BP field-effect transistor (FET) and a BP/MoTe2(2H + 1T′) heterojunction FET displays the characteristics of binary logic. However, a drain voltage-controlled transition from binary to ternary logic has been observed in BP FET- and BP/ MoTe2(2H) heterojunction FET-based logic circuits. Also, a change from binary to ternary characteristics has been observed in BP/MoTe2(2H)-based inverters at low temperature below 240 K. We believe that this work will stimulate the assessment of the structural phase transition in metal dichalcogenides toward advanced logic circuits and offer a pathway to substantialize the circuit standards for future MVL systems.

As Coulomb drag near charge neutrality (CN) is driven by fluctuations or inhomogeneity in charge density, the topology should play an extremely important role. Interlinking Coulomb drag and topology could reveal how the system’s nontrivial topology influences the electron–electron interactions at the quantum level. However, such an aspect is overlooked as most studies focus on symmetric drag systems without topology. To understand this topological aspect, we need to study Coulomb drag in an asymmetric system with a broken inversion symmetry and strong spin–orbit coupling (SOC). Here we experimentally demonstrate the energy-driven Coulomb drag in an asymmetric van der Waals heterostructure composed of black phosphorus and rhenium disulfide characterized by broken inversion symmetry. Temperature-dependent transport measurements near CN provide compelling evidence for the energy-driven Coulomb drag due to electron–hole coupling that is energetically favored in a broken-gap heterojunction, as confirmed by Hall coefficient sign reversal with temperature. Moreover, contrary to the symmetric devices, our results exhibit magnetic-field-free, i.e., topology-driven, Hall drag, revealing an intrinsic coupling between energy and charge modes. This is the manifestation of nonzero Berry curvature, akin to a magnetic field in momentum space, in a Rashba system, which arises from the SOC and broken inversion symmetry of the heterostructure.

The broken-gap (type III) van der Waals heterojunction is of particular interest, as there is no overlap between energy bands of its two stacked materials. Despite several studies on straddling-gap (type I) and staggered-gap (type II) vdW heterojunctions, comprehensive understanding of current transport and optoelectronic effects in a type-III heterojunction remains elusive. Here, we report gate-tunable current rectifying characteristics in a black phosphorus (BP)/rhenium disulfide (ReS2) type-III p–n heterojunction diode. Current transport in this heterojunction was modeled using the Simmons approximation through direct tunneling and Fowler–Nordheim tunneling in lower- and higher-bias regimes, respectively. We showed that a p–n diode based on a type-III heterojunction is mainly governed by tunneling-mediated transport, but that transport in a type-I p–n heterojunction is dominated by majority carrier diffusion in the higher-bias regime. Upon illumination with a 532 nm wavelength laser, the BP/ReS2type-III p–n heterojunction showed a photo responsivity of 8 mA/W at a laser power as high as 100 μW and photovoltaic energy conversion with an external peak quantum efficiency of 0.3%. Finally, we demonstrated a binary inverter consisting of BP p-channel and ReS2n-channel thin film transistors for logic applications.

Alternating current dielectrophoresis (DEP) is an excellent technique to assemble nanoscale materials. For efficient DEP, the optimization of the key parameters like peak-to-peak voltage, applied frequency, and processing time is required for good device. In this work, we have assembled graphene oxide (GO) nanostructures mixed with platinum (Pt) nanoparticles between the micro gap electrodes for a proficient hydrogen gas sensors. The Pt-decorated GO nanostructures were well located between a pair of prepatterned Ti/Au electrodes by controlling the DEP technique with the optimized parameters and subsequently thermally reduced before sensing. The device fabricated using the DEP technique with the optimized parameters showed relatively high sensitivity (∼10%) to 200 ppm hydrogen gas at room temperature. The results indicates that the device could be used in several industry applications, such as gas storage and leak detection.