Karsten Horn

Bio: Karsten Horn is an academic researcher from Max Planck Society. The author has contributed to research in topics: Graphene & Angle-resolved photoemission spectroscopy. The author has an hindex of 53, co-authored 285 publications receiving 16750 citations. Previous affiliations of Karsten Horn include University of London & Leipzig University.

Controlling the Electronic Structure of Bilayer Graphene

Abstract: We describe the synthesis of bilayer graphene thin films deposited on insulating silicon carbide and report the characterization of their electronic band structure using angle-resolved photoemission. By selectively adjusting the carrier concentration in each layer, changes in the Coulomb potential led to control of the gap between valence and conduction bands. This control over the band structure suggests the potential application of bilayer graphene to switching functions in atomic-scale electronic devices.

Towards wafer-size graphene layers by atmospheric pressure graphitization of silicon carbide

Abstract: Graphene, a single monolayer of graphite, has recently attracted considerable interest owing to its novel magneto-transport properties, high carrier mobility and ballistic transport up to room temperature. It has the potential for technological applications as a successor of silicon in the post Moore's law era, as a single-molecule gas sensor, in spintronics, in quantum computing or as a terahertz oscillator. For such applications, uniform ordered growth of graphene on an insulating substrate is necessary. The growth of graphene on insulating silicon carbide (SiC) surfaces by high-temperature annealing in vacuum was previously proposed to open a route for large-scale production of graphene-based devices. However, vacuum decomposition of SiC yields graphene layers with small grains (30-200 nm; refs 14-16). Here, we show that the ex situ graphitization of Si-terminated SiC(0001) in an argon atmosphere of about 1 bar produces monolayer graphene films with much larger domain sizes than previously attainable. Raman spectroscopy and Hall measurements confirm the improved quality of the films thus obtained. High electronic mobilities were found, which reach mu=2,000 cm (2) V(-1) s(-1) at T=27 K. The new growth process introduced here establishes a method for the synthesis of graphene films on a technologically viable basis.

Quasiparticle dynamics in graphene

Abstract: The effectively massless, relativistic behaviour of graphene’s charge carriers—known as Dirac fermions—is a result of its unique electronic structure, characterized by conical valence and conduction bands that meet at a single point in momentum space (at the Dirac crossing energy). The study of many-body interactions amongst the charge carriers in graphene and related systems such as carbon nanotubes, fullerenes and graphite is of interest owing to their contribution to superconductivity and other exotic ground states in these systems. Here we show, using angle-resolved photoemission spectroscopy, that electron–plasmon coupling plays an unusually strong role in renormalizing the bands around the Dirac crossing energy—analogous to mass renormalization by electron–boson coupling in ordinary metals. Our results show that electron–electron, electron–plasmon and electron–phonon coupling must be considered on an equal footing in attempts to understand the dynamics of quasiparticles in graphene and related systems.

Interlayer Interaction and Electronic Screening in Multilayer Graphene Investigated with Angle-Resolved Photoemission Spectroscopy

Abstract: The unusual transport properties of graphene are the direct consequence of a peculiar bandstructure near the Dirac point. We determine the shape of the {pi} bands and their characteristic splitting, and find the transition from two-dimensional to bulk character for 1 to 4 layers of graphene by angle-resolved photoemission. By detailed measurements of the {pi} bands we derive the stacking order, layer-dependent electron potential, screening length and strength of interlayer interaction by comparison with tight binding calculations, yielding a comprehensive description of multilayer graphene's electronic structure.

Interlayer Interaction and Electronic Screening in Multilayer Graphene

Abstract: Interlayer interaction and electronic screening in multilayer graphene Taisuke Ohta, 1, 2 Aaron Bostwick, 1 J. L. McChesney, 1, 3 Thomas Seyller, 4 Karsten Horn, 2 and Eli Rotenberg 1 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, USA Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany Montana State University, Bozeman, Montana, USA Institut f¨ r Physik der Kondensierten Materie, Universit¨ t Erlangen-N¨ rnberg, Erlangen, Germany u a u (Dated: March 30, 2007) The unusual transport properties of graphene are the direct consequence of a peculiar bandstruc- ture near the Dirac point. We determine the shape of the π bands and their characteristic splitting, and find the transition from two-dimensional to bulk character for 1 to 4 layers of graphene by angle-resolved photoemission. By detailed measurements of the π bands we derive the stacking order, layer-dependent electron potential, screening length and strength of interlayer interaction by comparison with tight binding calculations, yielding a comprehensive description of multilayer graphene’s electronic structure. PACS numbers: Much recent attention has been given to the electronic structure of multilayer films of graphene, the honeycomb carbon sheet which is the building block of graphite, car- bon nanotubes, C 60 , and other mesoscopic forms of car- bon [1]. Recent progress in synthesizing or isolating mul- tilayer graphene films [2–4] has provided access to their physical properties, and revealed many interesting trans- port phenomena, including an anomalous quantum Hall effect [5, 6], ballistic electron transport at room temper- ature [7], micron-scale coherence length [7, 8] and novel many-body couplings [9]. These effects originate from the effectively massless Dirac Fermion character of the carri- ers derived from graphene’s valence bands, which exhibit a linear dispersion degenerate near the so-called Dirac point energy, E D [10]. These unconventional properties of graphene offer a new route to room temperature, molecular-scale electron- ics capable of quantum computing [6, 7]. For example, a possible switching function in bilayer graphene has been suggested by reversibly lifting the band degeneracy at the Fermi level (E F ) upon application of an electric field [11, 12]. This effect is due to a unique sensitivity of the bandstructure to the charge distribution brought about by the interplay between strong interlayer hopping and weak interlayer screening, neither of which are currently well-understood [13, 14]. In order to evaluate the interlayer screening, stack- ing order and interlayer coupling, we have systemati- cally studied the evolution of the bandstructure of one to four layers of graphene using angle-resolved photoemis- sion spectroscopy (ARPES). We demonstrate experimen- tally that the interaction between layers and the stacking sequence affect the topology of the π bands, the former inducing an electronic transition from two-dimensional (2D) to 3D (bulk) character when going from one layer to multilayer graphene. The interlayer hopping integral and screening length are determined as a function of the num- ber of graphene layers by exploiting the sensitivity of π FIG. 1: (color online) Photoemission images revealing the bandstructure of (a) single and (b) bilayer graphene along high symmetry directions, Γ-K-M-Γ. The blue dashed lines are scaled DFT bandstructure of free standing films [16]. Inset in (a) shows the 2D Brillouin zone of graphene. states to the Coulomb potential, and the layer-dependent carrier concentration is estimated. The films were synthesized on n-type (nitrogen, 1 × 10 18 cm −3 ) 6H-SiC(0001) substrates (SiCrystal AG) that were etched in hydrogen at 1550 C. Annealing in a vac- uum first removes the resulting silicate adlayer and then causes the growth of the graphene layers between 1250 to 1400 C [15]. Beyond the first layer, the samples have a ± 0.5 monolayer thickness variation; the bandstructures of different thicknesses were extracted using the method of Ref. [11]. ARPES measurements were conducted at the Electronic Structure Factory endstation at beamline 7.01 of the Advanced Light Source, equipped with a Sci- enta R4000 electron energy analyzer. The samples were cooled to ∼ 30K by liquid He. The photon energy was 94 eV with the overall energy resolution of ∼30 meV for Fig. 1 and Fig. 2(a-d). The bandstructures of a single (Fig. 1 (a)) and a bi-

The rise of graphene

Abstract: 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.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

The electronic properties of graphene

Abstract: 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.

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

Abstract: 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。