Phys.org April 4, 2024 Moiré-pattern-based potential engineering has become an important way to explore exotic physics in a variety of two-dimensional condensed matter systems. An international team of researchers (Spain, Singapore) demonstrated theoretically that a single layer of graphene, when placed between two bulk boron nitride crystal substrates with the appropriate twist angles, could support a robust topological ultra flat band emerging as the second hole band. According to the researchers this is one of the simplest platforms to design and exploit topological flat bands… read more. TECHNICAL ARTICLE
Tag Archives: Graphene
Electrons become fractions of themselves in graphene
Science Daily February 21, 2024 The fractional quantum anomalous Hall effect (FQAHE), the analogue of the fractional quantum Hall effect at zero magnetic field, is predicted to exist in topological flat bands under spontaneous time-reversal-symmetry breaking. The demonstration of FQAHE could lead to non-Abelian anyons that form the basis of topological quantum computation. So far, FQAHE has been observed only in twisted MoTe2 at a moiré filling factor v > 1/2. Graphene-based moiré superlattices are believed to host FQAHE with the potential advantage of superior material quality and higher electron mobility. At zero magnetic field, an international team of researchers (USA – […]
Efficient fuel-molecule sieving using graphene
Phys.org September 22, 2023 Proton exchange membranes with high proton conductivity and low crossover of fuel molecules are required to realize advanced fuel-cell technology. The selective transportation of protons, which occurs by blocking the transportation of fuel molecules across a proton exchange membrane, is crucial to suppress crossover while maintaining a high proton conductivity. An international team of researchers (Japan, Germany) proposed a simple yet powerful method for optimizing the crossover-conductivity relationship by pasting sulfanilic-functionalized holey graphenes onto a Nafion membrane. Their results showed that the sulfanilic-functionalized holey graphenes supported by the membrane suppressed the crossover by 89% in methanol […]
‘Countercation engineering’ for thermoresponsive graphene-oxide nanosheets
Phys.org August 31, 2023 Thermoresponsive graphene-oxide (GO) nanosheets have been widely employed to develop smart membranes/surfaces, hydrogel actuators, recyclable systems, and biomedical applications. Current synthetic strategies to generate thermoresponsive GO nanosheets have exclusively relied on the covalent or non-covalent modification of their surfaces with thermoresponsive polymers. Researchers in Japan discovered that GO nanosheets with Bu4N+ countercations became thermoresponsive in water without the use of any thermoresponsive polymers, inducing a reversible sol–gel transition via their self-assembly and disassembly processes. The resultant dispersion can be used as a direct writing ink for constructing a three-dimensionally designable gel architecture of the GO nanosheets. […]
Scientists design novel nonlinear circuit to harvest clean power using graphene
Phys.org August 18, 2023 An international team of researchers (USA – University of Arkansas, UC Berkeley, Spain) theoretically considered a graphene ripple as a Brownian particle coupled to an energy storage circuit. When circuit and particle are at the same temperature, the second law forbids harvesting energy from the thermal motion of the Brownian particle, even if the circuit contains a rectifying diode. However, when the circuit contains a junction followed by two diodes wired in opposition, the approach to equilibrium may become ultraslow. Detailed balance is temporarily broken as current flows between the two diodes and charges storage capacitors. […]
Scientists use lasers to recreate ‘twisted’ superconducting material
Phys.org March 21, 2023 In strong correlations and superconductivity in twisted-bilayer graphene the superposition of two twisted honeycomb lattices generating a moiré pattern is the key to the observed flat electronic bands, slow electron velocity and large density of states. An international team of researchers (USA – University of Chicago, China) demonstrated quantum simulation of superfluid to Mott insulator transition in twisted-bilayer square lattices based on atomic Bose–Einstein condensates loaded into spin-dependent optical lattices. The lattices are made of two sets of laser beams that independently address atoms in different spin states, which form the synthetic dimension accommodating the two […]
Graphene quantum dots show promise as novel magnetic field sensors
Nanowerk March 6, 2023 Single quantum dots and coupled quantum dots formed with massless Dirac fermions can be viewed as artificial relativistic atoms and molecules, respectively. Such structures offer a unique testbed to study atomic and molecular physics in the ultrarelativistic regime. An international team of researchers (USA – UC Santa Cruz, UK, Japan) used a scanning tunnelling microscope to create and probe single and coupled electrostatically defined graphene quantum dots to unravel the magnetic-field responses of artificial relativistic nanostructures. When electrons in graphene are confined in a quantum dot, they travel in circular loops around the edge of the […]
Smooth sailing for electrons in graphene: Measuring fluid-like flow at nanometer resolution
Phys.org February 16, 2023 Electron flow in conductors becomes viscous when electron-electron collisions dominate over collisions with defects and other sources of resistance. An international team of researchers (USA – University of Wisconsin, Japan) investigated such behavior by using scanning tunneling potentiometry to probe the nanometer-scale flow of electron fluids in graphene as they pass through channels defined by smooth and tunable in-plane p-n junction barriers. They observed that as the sample temperature and channel widths were increased, the electron fluid flow underwent a Knudsen-to-Gurzhi transition from the ballistic to the viscous regime characterized by a channel conductance that exceeded […]
Unexpected speed-dependent friction with graphene
Nanowerk, December 6, 2022 Graphene is being examined with a view to potential use as a lubricating layer. If it is applied to a platinum surface, it has a significant impact on the measurable friction forces. An international team of researchers (Israel, Switzerland) has reported that, in this instance, the friction depends on the speed at which the tip of an atomic force microscope (AFM) is moved across the surface. In conjunction with the platinum substrate, graphene no longer forms only the hexagonal honeycomb pattern of carbon atoms and instead forms Moiré superlattices. The surface is then no longer completely […]
Physicists discover a “family” of robust, superconducting graphene structures
MIT News July 8, 2022 Despite multitudes of correlated phases observed in moiré systems, robust superconductivity appears the least common, found only in magic-angle twisted bilayer graphene (MATBG) and more recently in magic-angle twisted trilayer graphene. An international team of researchers (USA – MIT, Japan) has reported experimental realization of superconducting magic-angle twisted four-layer and five-layer graphene, hence establishing alternating twist magic-angle multilayer graphene as a robust family of moiré superconductors. This finding suggests that the flat bands shared by the members play a central role in the superconductivity. Their measurements in parallel magnetic fields reveal a clear distinction between […]