Graphene is a rapidly rising star on the horizon of materials science and condensed-matter physics. This strictly two-dimensional material exhibits exceptionally high crystal and electronic quality, and, despite its short history, has already revealed a cornucopia of new physics and potential applications, which are briefly discussed here. Whereas one can be certain of the realness of applications only when commercial products appear, graphene no longer requires any further proof of its importance in terms of fundamental physics. Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena, some of which are unobservable in high-energy physics, can now be mimicked and tested in table-top experiments. More generally, graphene represents a conceptually new class of materials that are only one atom thick, and, on this basis, offers new inroads into low-dimensional physics that has never ceased to surprise and continues to provide a fertile ground for applications.

The rise of graphene

Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

This article reviews the basic theoretical aspects of graphene, a one-atom-thick allotrope of carbon, with unusual two-dimensional Dirac-like electronic excitations. The Dirac electrons can be controlled by application of external electric and magnetic fields, or by altering sample geometry and/or topology. The Dirac electrons behave in unusual ways in tunneling, confinement, and the integer quantum Hall effect. The electronic properties of graphene stacks are discussed and vary with stacking order and number of layers. Edge (surface) states in graphene depend on the edge termination (zigzag or armchair) and affect the physical properties of nanoribbons. Different types of disorder modify the Dirac equation leading to unusual spectroscopic and transport properties. The effects of electron-electron and electron-phonon interactions in single layer and multilayer graphene are also presented.

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The electronic properties of graphene

Quantum electrodynamics (resulting from the merger of quantum mechanics and relativity theory) has provided a clear understanding of phenomena ranging from particle physics to cosmology and from astrophysics to quantum chemistry. The ideas underlying quantum electrodynamics also influence the theory of condensed matter, but quantum relativistic effects are usually minute in the known experimental systems that can be described accurately by the non-relativistic Schrodinger equation. Here we report an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation. The charge carriers in graphene mimic relativistic particles with zero rest mass and have an effective 'speed of light' c* approximately 10(6) m s(-1). Our study reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions. In particular we have observed the following: first, graphene's conductivity never falls below a minimum value corresponding to the quantum unit of conductance, even when concentrations of charge carriers tend to zero; second, the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; and third, the cyclotron mass m(c) of massless carriers in graphene is described by E = m(c)c*2. This two-dimensional system is not only interesting in itself but also allows access to the subtle and rich physics of quantum electrodynamics in a bench-top experiment.

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Two-dimensional gas of massless Dirac fermions in graphene

抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Carbon fibres (CF) represent a significant volume fraction of modern structural airframes. Embedded into polymer matrices, they provide significant strength and stiffness gains over unit weight as compared to other competing structural materials. Most CF are known to be fully turbostratic, consisting of graphene layers slipped sideways relative to each other, which leads to an inter-graphene distance much greater than graphite. Here, we use the Raman G peak to assess the response to strain CF with reference to graphene itself [1]. Our results highlight the predominance of the in-plane graphene properties in all complex graphitic structures examined. A universal master plot relating the G peak strain sensitivity to tensile modulus of all types of CF, as well as graphene, is presented. We derive a universal value of average phonon shift rate with axial stress , where is the G peak position at zero stress, for both graphene and CF with annular morphology [1]. The use of this for stress measurements in a variety of applications is discussed.

Universal stress evaluation in graphene and carbon fibres

Indirect excitons (IXs) in van der Waals transition-metal dichalcogenide (TMD) heterostructures are characterized by a high binding energy making them stable at room temperature and giving the opportunity for exploring fundamental phenomena in excitonic systems and developing excitonic devices operational at high temperatures. We present the observation of IXs at room temperature in van der Waals TMD heterostructures based on monolayers of MoS$_2$ separated by atomically thin hexagonal boron nitride. The IXs realized in the TMD heterostructure have lifetimes orders of magnitude longer than lifetimes of direct excitons in single-layer TMD, and their energy is gate controlled.

Indirect excitons in van der Waals heterostructures at room temperature

We report on magnetometry of individual Al disks with the radiusr from several μm down to 103A. The studies were carried out using a novel μ-magnetisation measurement technique which is based on detection of a local magnetic field by submicron Hall probes. The technique allows non-invasive access to individual superconducting samples of the size comparable with the coherence length ξ(T=0) (0D regime). The superconducting phase diagram of Al disks exhibits an oscillatory behaviour due to the size quantization in the energy spectrum of Cooper pairs, in analogy to the classical Little-Parks experiment. The experiment also reveals a number of new features related to the reduced dimensionality: a) recovery of the type-I phase transition aroundr=ξ(0) while the transition remains type-II in both limitsr >ξ b) mesoscopic correction to the ideal Meissner state due to partial penetration of a vortex and c) metastable superconductivity due to a hysteretic transition between the ground and excited states in the superconducting energy spectrum.

Magnetisation of individual mesoscopic superconductors

This paper describes some recent developments in our understanding of quantum transport phenomena in mesoscopic semiconducting structures. Two types of structure are considered: ultra-small wires of a degenerate semiconductor in the presence of a strong magnetic field and small-area resonant tunneling diodes. There are already some excellent review articles on universal conductance fluctuations and quantum interference effects in mesoscopic metallic and semiconducting structures in the linear transport regime. Therefore this subject is dealt with only briefly in the following section, which also highlights some recent work on the magnetoresistance of semiconducting n + GaAs wires in the high magnetic field regime. The paper then goes on to describe the manifestation of mesoscopic effects in small-area resonant tunneling devices, which are inherently non-linear conductors, exhibiting strong deviations from Ohm’s Law behavior.

Andre K. Geim

Papers

Universal stress evaluation in graphene and carbon fibres

Indirect excitons in van der Waals heterostructures at room temperature

Magnetisation of individual mesoscopic superconductors

Some Recent Developments in Quantum Transport in Mesoscopic Structures and Quantum Wells

Ultra-sensitive terahertz detection with 2d tunnel field-effect transistors