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A reexamination of the effective fine structure constant of graphene, as measured in graphite  [PDF]
Yu Gan,Gilberto de la Pena Munoz,Anshul Kogar,Bruno Uchoa,Diego Casa,Thomas Gog,Eduardo Fradkin,Peter Abbamonte
Physics , 2015,
Abstract: We present a refined and improved study of the influence of screening on the effective fine structure constant of graphene, $\alpha^\ast$, as measured in graphite using inelastic x-ray scattering. This follow-up to our previous study[1] was carried out with two times better momentum resolution, five times better energy resolution, and improved techniques for reducing experimental background. We compare our results to RPA calculations and evaluate the relative importance of interlayer hopping, excitonic corrections, and screening from higher energy excitations. We find that the static, limiting value of $\alpha^\ast$ falls in the range 0.25 to 0.35, which is higher than our previous result of 0.14[1], but still below the value expected from RPA. Graphitic effects from interlayer hopping were found to play a negligible role in the range of momenta studied. Instead, the anomalous screening was found to arise from a combination of excitonic effects in the $\pi \rightarrow \pi^\ast$ continuum and screening from the tightly bound $\sigma$-bands. Both effects appear to fade in the limit of low momentum, suggesting a recovery of RPA in the asymptotic limit, but should have significant influence on low-energy measurements on length scales less than a few nm, such as STM.
Atomic Control of Strain in Freestanding Graphene  [PDF]
P. Xu,Y. Yang,S. D. Barber,M. L. Ackerman,J. K. Schoelz,D. Qi,I. A. Kornev,L. Dong,L. Bellaiche,S. Barraza-Lopez,P. M. Thibado
Physics , 2015,
Abstract: In this study, we describe a new experimental approach based on constant-current scanning tunneling spectroscopy to controllably and reversibly pull freestanding graphene membranes up to 35 nm from their equilibrium height. In addition, we present scanning tunneling microscopy (STM) images of freestanding graphene membranes with atomic resolution. Atomic-scale corrugation amplitudes 20 times larger than the STM electronic corrugation for graphene on a substrate were observed. The freestanding graphene membrane responds to a local attractive force created at the STM tip as a highly-conductive yet flexible grounding plane with an elastic restoring force. We indicate possible applications of our method in the controlled creation of pseudo-magnetic fields by strain on single-layer graphene.
The Meaning Of The Fine Structure Constant  [PDF]
R. L. Oldershaw
Physics , 2007,
Abstract: A possible explanation is offered for the longstanding mystery surrounding the meaning of the fine structure constant. The reasoning is based on a discrete self-similar cosmological paradigm that has shown promise in explaining the general scaling properties of nature's global hierarchy. The discrete scale invariance of the paradigm implies that "strong gravity" governs gravitational interactions within atomic scale systems. Given the revised gravitational coupling constant and Planck mass, one can demonstrate that the fine structure constant is the ratio of the strengths of the unit electromagnetic interaction and the unit gravitational interaction within atomic scale systems. [Abridged]
Determination of the Fine Structure Constant by $π$  [PDF]
Anastass Anastasov
Physics , 1997,
Abstract: In the present report the author presents a simple and systematically defined formula for the fine structure constant based only on the number $\pi$. The difference between the suggested value and the currently known experimental one is about 60 times smaller than the uncertainty interval.
Quasi-freestanding and single-atom thick layer of hexagonal boron nitride as a substrate for graphene synthesis  [PDF]
D. Usachov,D. Haberer,A. Grüneis,H. Sachdev,A. B. Preobrajenski,V. K. Adamchuk,C. Laubschat,D. V. Vyalikh
Physics , 2010, DOI: 10.1103/PhysRevB.82.075415
Abstract: We demonstrate that freeing a single-atom thick layer of hexagonal boron nitride (hbn) from tight chemical bonding to a Ni(111) thin film grown on a W(110) substrate can be achieved by intercalation of Au atoms into the interface. This process has been systematically investigated using angle-resolved photoemission spectroscopy, X-ray photoemission and absorption techniques. It has been demonstrated that the transition of the hbn layer from the "rigid" into the "quasi-freestanding" state is accompanied by a change of its lattice constant. Using chemical vapor deposition, graphene has been successfully synthesized on the insulating, quasi-freestanding hbn monolayer. We anticipate that the in situ synthesized weakly interacting graphene/hbn double layered system could be further developed for technological applications and may provide perspectives for further inquiry into the unusual electronic properties of graphene.
Aging of the Universe and the fine structure constant  [PDF]
M. Kozlowski,J. Marciak-Kozlowska
Physics , 2003,
Abstract: In this paper the aging of the Universe is investigated in the frame of quantum hyperbolic heat transport equation. For the open universe, when t to \infty, hbar to \infty, c to 0 and fine structure constant alpha is constant. Key words: Quantum heat transport; Open universe; Fine structure constant.
Optical transparency of graphene as determined by the fine-structure constant  [PDF]
Daniel E. Sheehy,Joerg Schmalian
Physics , 2009, DOI: 10.1103/PhysRevB.80.193411
Abstract: The observed 97.7% optical transparency of graphene has been linked to the value 1/137 of the fine structure constant, by using results for noninteracting Dirac fermions. The agreement in three significant figures requires an explanation for the apparent unimportance of the Coulomb interaction. Using arguments based on Ward identities, the leading corrections to the optical conductivity due to the Coulomb interactions are correctly computed (resolving a subtle theoretical issue) and shown to amount to only 1-2%, corresponding to 0.03-0.04% in the transparency.
An Alternative to the Variation of the Fine Structure Constant  [PDF]
Mario Everaldo de Souza
Physics , 2003,
Abstract: It is considered that quasars evolve into normal galaxies by means of expansion of matter. The order of magnitude of the expansion velocity can be estimated. The Doppler shift caused by such expansion explains the supposed variation of the fine structure constant. This variation has been based on observations of absorption lines of gas clouds seen against background quasars. These ideas maintain the constancy of the fine structure constant.
Habitable sphere and fine structure constant  [PDF]
Miroslaw Kozlowski,Janina Marciak-Kozlowska
Physics , 2005,
Abstract: Future space missions, TPF and Darwin will focus on searches of signatures of life on extrasolar planets. In this paper we look for model independ definition of the habitable zone. It will be shown that the radius of the habitable sphere depends only on the constants of the Nature. Key words: Habitable sphere, fine structure constant.
On the fine structure constant in the Machian universe  [PDF]
Merab Gogberashvili,Igor Kanatchikov
Physics , 2010,
Abstract: Within the Machian model of the universe the dark energy is identified with the Machian energy of collective gravitational interactions of all particles inside the horizon. It is shown that the fine structure constant can be expressed in terms of the observed radiative, baryon and dark energy densities of the universe and the densities of various matter components are interrelated via it.
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