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

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

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

A detailed characterization of magnetic oxide films is essential to enable their use in magnetoresistive devices since their properties depend critically on stoichiometry and structural order. Here, the composition and magnetic properties of ultrathin iron oxide films grown epitaxially on Al2O3(0001) have been characterized using x-ray magnetic circular dichroism XMCD and magnetoresistance (MR) measurements. The XMCD data show by comparison with theoretical calculations that we have successfully found growth conditions for well ordered epitaxial films with Fe3O4 stoichiometry. Nonstoichiometric films exhibit, in addition to a relative reduction in Fe2+ ions, a net transfer of Fe3+ from tetrahedral to octahedral sites. The in-plane MR for both these films is found to be 1% at room temperature in a field of 1 T even though the electrical conductivity differs by a factor of 5.

Magnetic properties of stoichiometric and nonstoichiometric ultrathin Fe3O4(111) films on Al2O3(0001)

We present composite plasmonic nanostructures designed to achieve cascaded enhancement of electromagnetic fields at optical frequencies. Our structures were made with the help of electron-beam lithography and comprise a set of metallic nanodisks placed one above another. The optical properties of reproducible arrays of these structures were studied by using scanning confocal Raman spectroscopy. We show that our composite nanostructures robustly demonstrate dramatic enhancement of the Raman signals when compared to those measured from constituent elements.

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Cascaded Optical Field Enhancement in Composite Plasmonic Nanostructures

We present results from composite plasmonic nanostructures designed to achieve the cascaded enhancement of electromagnetic fields at optical frequencies. Our structures comprise a small metallic nanodisc suspended above a larger disk. We probe the optical properties of these structures by coating them with a layer of a visible-light fluorophore and observing fluorescence signals with the help of scanning confocal microscopy. A 43 ± 5-fold increase in the far-field fluorescence signal has been observed for two-tier composite nanostructures, when compared to the signal obtained from individual nanodiscs. Our results offer the prospect of using such nanostructures for field concentration, optical manipulation of nanoobjects, chemical and biological sensing.

http://www.condmat.physics.manchester.ac.uk/pdf/mesoscopic/publications/graphene/Nano.Lett%202010.%20composite%20Au%20nanostructures.pdf

Composite au nanostructures for fluorescence studies in visible light.

The magnetic properties of an eight-monolayer ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}(111)$ film grown epitaxially on Pt(111) have been studied by the magneto-optic Kerr effect (MOKE) and conversion electron M\"ossbauer spectroscopy. The MOKE results indicate that a saturation of the magnetization is achieved with a field of about 500 Oe. In zero field the magnetization remains saturated. Apart from a paramagnetic contribution of 11%, which is interpreted as originating from the interface layer, the M\"ossbauer spectrum is identical to that of bulk ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}.$ Furthermore, the data indicate that all the magnetic moments are in the plane of the film.

In-plane magnetization of an ultrathin film of Fe3O4(111) grown epitaxially on Pt(111)

We study optical properties of optomagnetic metamaterials produced by regular arrays of double gold dots (nanopillars). Using combined data of spectroscopic ellipsometry, transmission and reflection measurements, we identify localized plasmon resonances of a nanopillar pair and measure their dependences on dot sizes. We formulate the necessary condition at which an effective field theory can be applied to describe optical properties of a composite medium and employ interferometry to measure phase shifts for our samples. A negative phase shift for transmitted green light coupled to an antisymmetric magnetic mode of a double-dot array is observed.

Fred Schedin

Papers

Magnetic properties of stoichiometric and nonstoichiometric ultrathin Fe3O4(111) films on Al2O3(0001)

Cascaded Optical Field Enhancement in Composite Plasmonic Nanostructures

Composite au nanostructures for fluorescence studies in visible light.

In-plane magnetization of an ultrathin film of Fe3O4(111) grown epitaxially on Pt(111)

Plasmonic resonances in optomagnetic metamaterials based on double dot arrays.