Steering the current flow in twisted bilayer graphene

A nanoelectronic device made of twisted bilayer graphene (TBLG) is proposed to steer the direction of the current flow. The ballistic electron current, injected at one edge of the bottom layer, can be guided predominantly to one of the lateral edges of the top layer. The current is steered to the opposite lateral edge, if either the twist angle is reversed or the electrons are injected in the valence band instead of the conduction band, making it possible to control the current flow by electric gates. When both graphene layers are aligned, the current passes straight through the system without changing its initial direction. The observed steering angle exceeds well the twist angle and emerges for a broad range of experimentally accessible parameters. It is explained by the twist angle and the trigonal shape of the energy bands beyond the van Hove singularity due to the Moiré interference pattern. As the shape of the energy bands depends on the valley degree of freedom, the steered current is valley polarized. Our findings show how to control and manipulate the current flow in TBLG. Technologically, they are of relevance for applications in twistronics and valleytronics.

Observation of ballistic upstream modes at fractional quantum Hall edges of graphene

The presence of “upstream” modes, moving against the direction of charge current flow in the fractional quantum Hall (FQH) phases, is critical for the emergence of renormalized modes with exotic quantum statistics. Detection of excess noise at the edge is a smoking gun for the presence of upstream modes. Here, we report noise measurements at the edges of FQH states realized in dual graphite-gated bilayer graphene devices. A noiseless dc current is injected at one of the edge contacts, and the noise generated at contacts at length, L = 4 μm and 10 μm away along the upstream direction is studied. For integer and particle-like FQH states, no detectable noise is measured. By contrast, for “hole-conjugate” FQH states, we detect a strong noise proportional to the injected current, unambiguously proving the existence of upstream modes. The noise magnitude remains independent of length, which matches our theoretical analysis demonstrating the ballistic nature of upstream energy transport, quite distinct from the diffusive propagation reported earlier in GaAs-based systems.

Anomalous change of carrier transport property of ferroelectric Hf0.5Zr0.5O2 thin films in the first poling treatment

Carrier transport properties of ferroelectric Hf0.5Zr0.5O2 (HZO) thin films have been investigated on metal-ferroelectric-metal (MFM) capacitor in the first current flow of ferroelectric poling treatment. In current–voltage (I–V) measurement of MFM capacitor, a kink or discontinuity point of derivative in I–V characteristic appears, and after the cyclic voltage sweep this kink disappears. This phenomenon is different from the ferroelectric instabilities after several thousand or million voltage cycle applies reported as the wake-up and fatigue. From the analysis using Poole-Frenkel plot of I–V characteristics, it is suggested that irreversible trap generation by electric field apply occurs in poling treatment.

Fuzzy Regulator for Two-Phase Gas–Liquid Pipe Flows Control

The paper presents an intelligent module to control dynamic two-phase gas–liquid mixtures pipelines flow processes. The module is intelligent because it uses the algorithm based on AI methods, namely, fuzzy logic inference, to build the fuzzy regulator concept. The developed modification has allowed to design and implement the black-box type regulator. Therefore, it is not required to determine any of the complicated computer models of the flow rig, which is unfortunately necessary when using the classic regulators. The inputs of the regulator are four linguistic variables that are decomposed into two classes and two methods of fuzzification. The first input class describes the current values of gas and liquid pipe flows, which at the same time are the controlled values manipulated to generate desired flow type. The second class of the input signals contains a current flow state, namely, its name and the name preferred by the operator flow type. This approach improves the control accuracy since the given flow type can be generated with different gas and liquid volume fractions. Those values can be optimized by knowing the current flow type. Moreover, the fuzzification algorithm used for the input signals included in the first-class covers the current crisp signal value and its trend making the inference more accurate and resistant to slight measurement system inaccuracy. This approach of defined input signals in such environments is used for the first time. Considering all mentioned methods, it is possible to generate the desired flow type by manipulating the system input signals by minimum required values. Furthermore, a flow type can be changed by adjusting only one of the input signals. As an output of the inference process, two linguistic values are received, which are fuzzified adjustment values of the liquid pump and gas flow meter. The regulator looks to be universal, and it can be adopted by multiple test and production rigs. Moreover, once configured with a dedicated rig, it can be easily operated by the non (domain) technical staff. The usage of fuzzy terms makes understanding both the control strategy working principles and the obtained results easy.

Bipolar Membrane and Water Splitting in Electrodialysis

The traditional view of the conductivity of electrolytes is based on the mobility of ions in an electric field. A new concept of water conductivity introduces an electron–hole mechanism known from semiconductor theory. The electrolyte ions in the hydrogen bond network of water imitate the structure of a doped silicon lattice. The source of the current carriers is the electrode reaction generating H+ and OH− ions. The continuity of current flow is provided through the electron–hole mechanism, and the movement of electrolyte ions is only a side process. Bipolar membrane in the semiconductor approach is an electrochemical diode forward biased. Generation of large amounts of H+ and OH− has to be considered as a result of current flow and does not require any increase in the water dissociation rate. Bipolar membranes are essential in electrodialysis stacks for the recovery of acids and bases by salt splitting. Graphic Abstract