Ultrafast lasers map electrons ‘going ballistic’ in graphene with implications for next-gen electronic devices

Phys.org December 15, 2023 Researchers at the University of Kansas formed heterostructure by sandwiching a MoS2 and MoSe2 heterobilayer between two graphene monolayers. Transient absorption measurements revealed that the electrons and holes separated by the type-II interface between MoS2 and MoSe2 could transfer to the two graphene layers, respectively. With high spatial and temporal resolution, they found that while the holes in one graphene layer undergoes a classical diffusion process with a large diffusion coefficient of 65 cm2 s–1 and a charge mobility of 5000 cm2 V–1 s–1, the electrons in the other graphene layer exhibits a quasi-ballistic transport feature. […]

Physicists turn pencil lead into metaphorical ‘gold’

Phys.org  October 30, 2023 Rhombohedral-stacked multilayer graphene hosts a pair of flat bands touching at zero energy, which should give rise to correlated electron phenomena that can be tuned further by an electric field. An international team of researchers (USA – MIT, Harvard University, Japan) measured electron transport through hexagonal boron nitride-encapsulated pentalayer graphene down to 100 mK and observed a correlated insulating state with resistance at the megaohm level or greater at charge density n = 0 and displacement field D = 0. By increasing D, they observed a Chern insulator state with C = −5 and two other states with C = −3 at a magnetic field […]

The right twist and strain for graphene to form 1D moirés

Phys.org   October 30, 2023 The formation of one-dimensional moiré patterns is a consequence of an interplay between twist and strain which gives rise to a collapse of the reciprocal space unit cell. An international team of researchers (Spain, Poland) found a simple relation between the two quantities and the material specific Poisson ratio. The induced one-dimensional behavior was characterized by two, usually incommensurate, periodicities. According to the researchers their results offer explanations for the complex patterns of one-dimensional channels observed in low angle twisted bilayer graphene systems and twisted bilayer dichalcogenides. Their findings can be applied to any hexagonal twisted […]

From a five-layer graphene sandwich, a rare electronic state emerges

Science Daily   October 18, 2023 Multiferroics have multifunctional electrical and magnetic device applications. Two-dimensional materials with honeycomb lattices offer opportunities to engineer unconventional multiferroicity. Orbital multiferroics could offer strong valley–magnetic couplings and large responses to external fields—enabling device applications such as multiple-state memory elements and electric control of the valley and magnetic states. An international team of researchers (USA – MIT, Harvard University, Japan) has shown orbital multiferroicity in Penta layer rhombohedral graphene. They observed anomalous Hall signals Rxy with an exceptionally large Hall angle and orbital magnetic hysteresis at hole doping. There were four such states with different valley […]

Experiments reveal that water can ‘talk’ to electrons in graphene

Nanowerk  June 23, 2023 Liquids induce electronic polarization and drive electric currents as they flow; electronic excitations, in turn, participate in hydrodynamic friction. Yet, the underlying solid–liquid interactions have been lacking a direct experimental probe. An international team of researchers (Germany, UK, Spain) heated graphene electron quasi-instantaneously by a visible excitation pulse and monitored the time evolution of the electronic temperature with a terahertz pulse. They observed that water accelerated the cooling of the graphene electrons, whereas other polar liquids leave the cooling dynamics largely unaffected. A quantum theory of solid–liquid heat transfer accounts for the water-specific cooling enhancement through […]

Ultra-lightweight multifunctional space skin created to withstand extreme conditions in space

Nanowerk  March 22, 2023 Current tissue engineering approaches combine different scaffold materials with living cells to provide biological substitutes that can repair and eventually improve tissue functions. Both natural and synthetic materials have been fabricated for transplantation of stem cells and their specific differentiation into muscles, bones, and cartilages. One of the key objectives for bone regeneration therapy to be successful is to direct stem cells’ proliferation and to accelerate their differentiation in a controlled manner using growth factors and osteogenic inducers. An international team of researchers (Singapore, South Korea) has shown that graphene provides a promising biocompatible scaffold that […]

Reaching superconductivity layer by layer

Phys.org  March 2, 2023 Multilayered graphene has many promising qualities ranging from widely tunable band structure and special optical properties to new forms of superconductivity. An international team of researchers (Austria, Israel) studied multilayer graphene for the possibility of creating topological superconductivity. In their theoretical model, simulated on a computer, they looked at various possible arrangements of different graphene sheets on top of each other and the behavior of electrons that move in the multiplayer graphene. Depending on how the different layers of graphene are shifted with respect to each other and on how many layers there were, the positively […]

Study: Superconductivity switches on and off in ‘magic-angle’ graphene

Pays.org January 30, 2023 Superconducting FETs operate through continuous tuning of carrier density, but no bistable superconducting FET, which could serve as a new type of cryogenic memory element, has been reported. Recently, gate hysteresis and resultant bistability in Bernal-stacked bilayer graphene aligned to its insulating hexagonal boron nitride gate dielectrics were discovered. An international team of researchers (USA- MIT, Israel) reported the observation of hysteresis in magic-angle twisted bilayer graphene (MATBG) with aligned boron nitride layers. The bistable behaviour coexists alongside the strongly correlated electron system of MATBG without disrupting its correlated insulator or superconducting states. The all-van der […]

At the edge of graphene-based electronics

Nanowerk  December 22, 2022 An international team of researchers (USA – Georgia Institute of Technology, National High Magnetic Field Laboratory, France) has demonstrated that the annealed edges in conventionally patterned graphene epitaxially grown on a silicon carbide substrate (epigraphene) are stabilized by the substrate and support a protected edge state. The edge state has a mean free path that is greater than 50 microns, 5000 times greater than the bulk states and involves a theoretically unexpected Majorana-like zero-energy non-degenerate quasiparticle that does not produce a Hall voltage. In seamless integrated structures, the edge state formed a zero-energy one-dimensional ballistic network […]

Simpler graphene method paves way for new era of nanoelectronics

Phys.org  March 15, 2022 The high electron mobility of graphene points to great potential for broadband communications and high-speed electronics operating at terahertz switching rates. However, complex, and expensive fabrication methods make it more expensive and hinder mass production of such devices. Researchers in Sweden proposed chemical vapor deposition (CVD) of graphene on commercial copper (Cu) foils providing a scalable route towards high-quality single-layer graphene. The graphene is grown on a metallic surface like Cu, Pt or Ir, after which it can be separated from the metal and transferred to specifically required substrates. The process can be simply explained as […]