Electronic and Vibrational Excitations on the Surface of the Three-Dimensional Topological Insulator Bi2_2Te3−x_{3-x}Sex_{x} (x = 0, 2, 3)

We study surface states in the three-dimensional topological insulators Bi$_2$Te$_{3-x}$Se$_{x}$ (x = 0, 2, 3) by polarization resolved resonant Raman spectroscopy. By tracking the spectral intensity of the surface phonon modes with respect to the incident photon energy, we show that the surface phonons are qualitatively similar to their bulk counterparts. Using the resonant Raman excitation profile, we estimated the binding energy of the surface conduction bands relative to bulk conduction bands. In addition, by analyzing the Fano interaction between the electronic continuum and the surface phonons as a function of incident photon energy, we determined the spectral properties of the electronic continuum excitations between surface and bulk states in Bi$_2$Se$_3$

R+R2R + R^2 Gravity as R+R + Backreaction

Quadratic theory of gravity is a complicated constraint system. We investigate some consequences of treating quadratic terms perturbatively (higher derivative version of backreaction effects). This approach is shown to overcome some well known problems associated with higher derivative theories, i.e., the physical gravitational degree of freedom remains unchanged from those of Einstein gravity. Using such an interpretation of $R + \beta R^2$ gravity, we investigate a classical and Wheeler DeWitt evolution of $R + \beta R^2$ gravity for a particular sign of $\beta$, corresponding to non- tachyon case. Matter is described by a phenomenological $\rho \propto a(t)^{-n}$. It is concluded that both the Friedmann potential $U(a)$ (${\dot a}^2 + 2U(a) = 0$) and the Wheeler DeWitt potential $W(a)$ ($\left[-{\partial^2\over \partial a^2} + 2W(a)\right]\psi (a) =0$) develop repulsive barriers near $a\approx 0$ for $n>4$ (i.e., $p > {1\over 3}\rho$). The interpretations is clear. Repulsive barrier in $U(a)$ implies that a contracting FRW universe ($k>0, k=0, k<0$) will bounce to an expansion phase without a total gravitational collapse. Repulsive barrier in $W(a)$ means that $a \approx 0$ is a classically forbidden region. Therefore, probability of finding a universe with the big bang singularity ($a=0$ ) is exponentially suppressed.Comment: Accepted for publication in Phy. Rev. D.,18 pages, 6 figures, Latex fil

Nonstoichiometric doping and Bi antisite defect in single crystal Bi2Se3

We studied the defects of Bi2Se3 generated from Bridgman growth of stoichiometric and nonstoichiometric self-fluxes. Growth habit, lattice size, and transport properties are strongly affected by the types of defect generated. Major defect types of Bi_Se antisite and partial Bi_2-layer intercalation are identified through combined studies of direct atomic-scale imaging with scanning transmission electron microscopy (STEM) in conjunction with energy-dispersive X-ray spectroscopy (STEM-EDX), X-ray diffraction, and Hall effect measurements. We propose a consistent explanation to the origin of defect type, growth morphology, and transport property.Comment: 5 pages, 5 figure

The Role of E-Books in the Future of the Supply Chain of the Publishing Industry

The intent of this paper is to explore the future role of ebooks in the publishing industry. Emphasis is put on the impact it has on the supply chain of the industry. Issues dealing with the legal ramifications and financial implications, such as sales taxes, will also be addressed. The first section describes characteristics of e-books and the current developments in e-books from the consumer’s point of view. With the handling of the content of publications in digital form, intellectual property rights will become more complex and will require new regulations to deal with the new medium. These and other related legal issues are addressed in the third section. With the likelihood of utilizing the Internet for the distribution of the e-book to consumers, the collection of sales taxes will be difficult for government agencies to handle. The situation will be further complicated due to the globalization of the market place. Which policies are in effect, how will they are enforced, and who are responsible for their collection are emerging issues that will need to be addressed in the global and local arenas. Then it will be followed by the impact it has on the supply chain of the industry. For example, one of the benefits of ebooks is the reduction of logistical costs throughout the supply chain. Also, due to the ease of distribution, there most likely will be consolidation of certain levels within the supply chain. It may trigger a shift of competitive power among the various levels. The likely scenario of the future business environment of the publishing industry is discussed in the concluding section