Strain-induced Evolution of Electronic Band Structures in a Twisted Graphene Bilayer

Here we study the evolution of local electronic properties of a twisted graphene bilayer induced by a strain and a high curvature. The strain and curvature strongly affect the local band structures of the twisted graphene bilayer; the energy difference of the two low-energy van Hove singularities decreases with increasing the lattice deformations and the states condensed into well-defined pseudo-Landau levels, which mimic the quantization of massive Dirac fermions in a magnetic field of about 100 T, along a graphene wrinkle. The joint effect of strain and out-of-plane distortion in the graphene wrinkle also results in a valley polarization with a significant gap, i.e., the eight-fold degenerate Landau level at the charge neutrality point is splitted into two four-fold degenerate quartets polarized on each layer. These results suggest that strained graphene bilayer could be an ideal platform to realize the high-temperature zero-field quantum valley Hall effect.Comment: 4 figure

Electrically tunable transverse magnetic focusing in graphene

Author's final manuscript January 9, 2013Electrons in a periodic lattice can propagate without scattering for macroscopic distances despite the presence of the non-uniform Coulomb potential due to the nuclei. Such ballistic motion of electrons allows the use of a transverse magnetic field to focus electrons. This phenomenon, known as transverse magnetic focusing (TMF), has been used to study the Fermi surface of metals and semiconductor heterostructures, as well as to investigate Andreev reflection and spin–orbit interaction, and to detect composite fermions. Here we report on the experimental observation of TMF in high-mobility mono-, bi- and tri-layer graphene devices. The ability to tune the graphene carrier density enables us to investigate TMF continuously from the hole to the electron regime and analyse the resulting focusing fan. Moreover, by applying a transverse electric field to tri-layer graphene, we use TMF as a ballistic electron spectroscopy method to investigate controlled changes in the electronic structure of a material. Finally, we demonstrate that TMF survives in graphene up to 300 K, by far the highest temperature reported for any system, opening the door to new room-temperature applications based on electron-optics.National Science Foundation (U.S.) (CAREER Award DMR-0845287)United States. Office of Naval Research. GATE MURI Projec

The factors that influence the reading habit among Malaysian: a systematic literature review

Reading is an action that a person does to obtain a wider knowledge through his or her experience and this process may lead that person into a very eye-opening self-discovery. In Malaysia, reading habits rate is still at a lower level, Malaysian on average read only two books per year. About 80% of Malaysian university students are reluctant readers. They can read but choose not to read. Therefore, the objective of this study is to identify the factors affecting the reading habit among Malaysia. To answer the research question of this study we performed a systematic literature review (SLR). We defined a mapping study process adapted from existing guidelines to categorize and to structure the research evidence that has been published in the area of reading habits among Malaysian and world-wide. Twenty-Four papers were used in our synthesis of evidence, and five factors were identified. The results of this SLR showed the five factors that can affect the reading habits among Malaysian: (1) Internet (2) Environmental influence (3) Lack of motivation (4) Peer pressure (5) Entertainment. The findings of this SLR would be beneficial for understanding the needs of Malaysian towards the reading habit by looking at the factors, that might be a measurement of reading habit environment in other specific scopes

Quantum dynamics in strong fluctuating fields

A large number of multifaceted quantum transport processes in molecular systems and physical nanosystems can be treated in terms of quantum relaxation processes which couple to one or several fluctuating environments. A thermal equilibrium environment can conveniently be modelled by a thermal bath of harmonic oscillators. An archetype situation provides a two-state dissipative quantum dynamics, commonly known under the label of a spin-boson dynamics. An interesting and nontrivial physical situation emerges, however, when the quantum dynamics evolves far away from thermal equilibrium. This occurs, for example, when a charge transferring medium possesses nonequilibrium degrees of freedom, or when a strong time-dependent control field is applied externally. Accordingly, certain parameters of underlying quantum subsystem acquire stochastic character. Herein, we review the general theoretical framework which is based on the method of projector operators, yielding the quantum master equations for systems that are exposed to strong external fields. This allows one to investigate on a common basis the influence of nonequilibrium fluctuations and periodic electrical fields on quantum transport processes. Most importantly, such strong fluctuating fields induce a whole variety of nonlinear and nonequilibrium phenomena. A characteristic feature of such dynamics is the absence of thermal (quantum) detailed balance.Comment: review article, Advances in Physics (2005), in pres

Van der Waals heterostructures

Research on graphene and other two-dimensional atomic crystals is intense and likely to remain one of the hottest topics in condensed matter physics and materials science for many years. Looking beyond this field, isolated atomic planes can also be reassembled into designer heterostructures made layer by layer in a precisely chosen sequence. The first - already remarkably complex - such heterostructures (referred to as 'van der Waals') have recently been fabricated and investigated revealing unusual properties and new phenomena. Here we review this emerging research area and attempt to identify future directions. With steady improvement in fabrication techniques, van der Waals heterostructures promise a new gold rush, rather than a graphene aftershock