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

We have used a nonlocal configuration of measurement probes to study the magnetoresistance of diffusive n+-GaAs wires at high magnetic fields where ωcτ>1. At low temperatures we observe universal conductance fluctuations (UCF). For ωcτ>1 there is a large increase in the Lee-Stone correlation field but the amplitude is unchanged in strong disagreement with the theoretical prediction. We conclude that the UCF in this regime cannot be scaled in terms of a single parameter, the phase coherence length. At higher temperatures, where the UCF are quenched, we observe qualitatively new magnetoresistance oscillations which have the same periodicity as Shubnikov-de Haas oscillations but differ from them in many important respects. In particular, the new oscillations disappear at low temperatures. This indicates the importance of dissipation in the measurement of nonlocal resistance. There is excellent agreement between the temperature dependence of the new oscillations and a simple model.

Nonlocal magnetoresistance of diffusive wires in high magnetic fields

Universal behaviour of the thermoelectric power of composite fermions

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Giant photo-effect in proton transport through graphene

We show that excess noise in micron-sized samples fabricated from Si-doped GaAs/GaAlAs quantum wells and heterostructures is a strong non-monotonic function of temperature with several sharp peaks below room temperature. The noise power at the peaks exceeds the background noise by several orders of magnitude. The observed behaviour represents a classical noise source where only a single type of switching defect with a well-defined activation energy is present. We attribute the resonances to deep metastable donors and provisionally identify one of the donors as the known DX-centre in GaAs and GaAlAs.

Giant temperature resonances of noise in submicron quantum well structures

Fine-tuned ion transport across nanoscale pores is key to many biological processes such as information processing in the brain. Recent experimental advances have enabled the confinement of water and ions down to two dimensions, unveiling specific transport properties unreachable at larger scales and triggering hopes to reproduce the advanced ionic machinery of biological systems. Here we report experiments demonstrating the emergence of memory in the transport of aqueous electrolytes across (sub-)nanoscale channels. Our study unveils two types of ionic memristor responses, depending on the type of channel material and confinement, with long-term memory – from minutes to hours. We rationalize these behaviors in terms of self-assembly or surface adsorption of ions and show how arbitrarily large timescales can emerge from coupling ion transport to interfacial processes. Such behavior allows us to implement Hebbian learning with nanofluidic systems using ions in water as charge carriers, similar to the way that neurons work. This lays the ground for biomimetic neuromorphic computations on aqueous electrolytic chips.

Andre K. Geim

Papers

Nonlocal magnetoresistance of diffusive wires in high magnetic fields

Universal behaviour of the thermoelectric power of composite fermions

Giant photo-effect in proton transport through graphene

Giant temperature resonances of noise in submicron quantum well structures

Long-term memory and synapse-like dynamics of ionic carriers in two-dimensional nanoﬂuidic channels