Surface States of the Topological Insulator Bi_{1-x}Sb_x

We study the electronic surface states of the semiconducting alloy BiSb. Using a phenomenological tight binding model we show that the Fermi surface of the 111 surface states encloses an odd number of time reversal invariant momenta (TRIM) in the surface Brillouin zone confirming that the alloy is a strong topological insulator. We then develop general arguments which show that spatial symmetries lead to additional topological structure, and further constrain the surface band structure. Inversion symmetric crystals have 8 Z_2 "parity invariants", which include the 4 Z_2 invariants due to time reversal. The extra invariants determine the "surface fermion parity", which specifies which surface TRIM are enclosed by an odd number of electron or hole pockets. We provide a simple proof of this result, which provides a direct link between the surface states and the bulk parity eigenvalues. We then make specific predictions for the surface state structure for several faces of BiSb. We next show that mirror invariant band structures are characterized by an integer "mirror Chern number", n_M. The sign of n_M in the topological insulator phase of BiSb is related to a previously unexplored Z_2 parameter in the L point k.p theory of pure Bi, which we refer to as the "mirror chirality", \eta. The value of \eta predicted by the tight binding model for Bi disagrees with the value predicted by a more fundamental pseudopotential calculation. This explains a subtle disagreement between our tight binding surface state calculation and previous first principles calculations on Bi. This suggests that the tight binding parameters in the Liu Allen model of Bi need to be reconsidered. Implications for existing and future ARPES experiments and spin polarized ARPES experiments will be discussed.Comment: 15 pages, 7 figure

Finite Temperature Casimir Effect and Dispersion in the Presence of Compactified Extra Dimensions

Finite temperature Casimir theory of the Dirichlet scalar field is developed, assuming that there is a conventional Casimir setup in physical space with two infinitely large plates separated by a gap R and in addition an arbitrary number q of extra compacified dimensions. As a generalization of earlier theory, we assume in the first part of the paper that there is a scalar 'refractive index' N filling the whole of the physical space region. After presenting general expressions for free energy and Casimir forces we focus on the low temperature case, as this is of main physical interest both for force measurements and also for issues related to entropy and the Nernst theorem. Thereafter, in the second part we analyze dispersive properties, assuming for simplicity q=1, by taking into account dispersion associated with the first Matsubara frequency only. The medium-induced contribution to the free energy, and pressure, is calculated at low temperatures.Comment: 25 pages, one figure. Minor changes in the discussion. Version to appear in Physica Script

Finite Temperature Casimir Effect in Randall-Sundrum Models

The finite temperature Casimir effect for a scalar field in the bulk region of the two Randall-Sundrum models, RSI and RSII, is studied. We calculate the Casimir energy and the Casimir force for two parallel plates with separation $a$ on the visible brane in the RSI model. High-temperature and low-temperature cases are covered. Attractiveness versus repulsiveness of the temperature correction to the force is discussed in the typical special cases of Dirichlet-Dirichlet, Neumann-Neumann, and Dirichlet-Neumann boundary conditions at low temperature. The Abel-Plana summation formula is made use of, as this turns out to be most convenient. Some comments are made on the related contemporary literature.Comment: 33 pages latex, 2 figures. Some changes in the discussion. To appear in New J. Phy

Performance Impacts of E-Government: An International Perspective

Though policy makers and governments are interested in understanding the impacts of e- Government on national performance, there are relatively few empirical studies that analyze this aspect. Using secondary data from 99 countries and the IT impact literature as the guiding theoretical perspective, we first examine the impact of e-Government on first order government efficiency parameters (resource allocation and internal operations efficiency) and subsequently the impact of these first order outcomes on the two second order dimensions of national performance (social welfare and business competitiveness). Our initial analysis reveals a significant relationship between e-government development and resource allocation efficiency and also between e-Government development and internal operations efficiency. For the second order model, we find that the relationship between internal operations efficiency and social welfare competitiveness is not significant. We conducted a post-hoc analysis which revealed that the relationship between internal operational efficiency and social welfare competitiveness is fully mediated through national business competitiveness. Hence, business competitiveness emerges as an important aspect for realizing the social welfare benefits of e-Government. Through this research, we make some important contributions and implications for researchers, practitioners and policy makers

Information Systems (IS) Discipline Identity: A Review and Framework

The recent debate about crisis in the Information Systems (IS) discipline is largely attributed to its having a fluid discipline identity. Myriad conceptualizations of IS discipline identity have resulted in a plethora of unstructured and disconnected recommendations for the survival and growth of the IS field. It is therefore essential to have a theoretical framework which explains: What is IS discipline identity? In this study, we address this void in the identity literature. By extending and borrowing from the concepts of organizational and self-identity, we propose a theoretical framework for discipline identity and explicate its dimensions with respect to the IS discipline. The three contextual questions of discipline identity about purpose, period, and place set the stage for an in-depth inquiry of the three constitutive questions (or dimensions): periphery, perspective, and process, to provide a holistic framework for conceptualizing IS discipline identity. Further, we conceptualize IS discipline identity process as consisting of four recursive and iterative sub-processes: copy, consolidate, differentiate, and demonstrate (CCDD). We posit that an iterative hermeneutic focus on these four sub-processes is vital for the health of the discipline and neglecting even one of them will lead to an imbalanced identity structure. Through this paper, we seek to stimulate and further the ongoing debate on the topic

Aligning Control Structures With Control Processes For Effective Offshore Contract Performance

Past research on offshore information systems development (ISD) has found control theory to be a useful perspective for examining the co-ordination between the client and the vendor. Control literature describes two primary control modes viz. formal and informal control modes, classified as behavior, outcome, clan and self-control modes. But most control literature focuses either on the conditions for adopting a particular control mode or the influence of the chosen control mode(s) on relationship performance. Recent research on offshore ISD has uncovered two distinct control mechanisms comprising each of the control modes viz. structural and process mechanisms. Structural control mechanism describes the ‘what’ or the structure of the control mode, whereas process control mechanism explains ‘how’ or the process through which the control mode is enacted. Grounding our arguments in the alignment literature, the study theorizes the need for alignment between the control ‘structures’ and ‘processes’ within each of the control modes for effective contract performance. In effect, we posit the moderating role of control processes on the relationship between control structures and contract performance. In this research-in- progress paper, we perform a preliminary test on the theorized model, through data collected from a field study comprising offshore ISD projects executed by Indian vendors. Initial results indicate support for the ‘alignment’ argument. In future, we intend to do detailed theorizing, and ultimately test the model for different dependent variables, thereby contributing to the literature on alignment and control theory for offshore ISD

Origins of ferromagnetism in transition-metal doped Si

We present results of the magnetic, structural and chemical characterizations of Mn<sup>+</sup>-implanted Si displaying <i>n</i>-type semiconducting behavior and ferromagnetic ordering with Curie temperature,T<sub>C</sub> well above room temperature. The temperature-dependent magnetization measured by superconducting quantum device interference (SQUID) from 5 K to 800 K was characterized by three different critical temperatures (T*<sub>C</sub>~45 K, T<sub>C1</sub>~630-650 K and T<sub>C2</sub>~805-825 K). Their origins were investigated using dynamic secondary mass ion spectroscopy (SIMS) and transmission electron microscopy (TEM) techniques, including electron energy loss spectroscopy (EELS), Z-contrast STEM (scanning TEM) imaging and electron diffraction. We provided direct evidences of the presence of a small amount of Fe and Cr impurities which were unintentionally doped into the samples together with the Mn<sup>+</sup> ions, as well as the formation of Mn-rich precipitates embedded in a Mn-poor matrix. The observed T*<sub>C</sub> is attributed to the Mn<sub>4</sub>Si<sub>7</sub> precipitates identified by electron diffraction. Possible origins of and are also discussed. Our findings raise questions regarding the origin of the high ferromagnetism reported in many material systems without a careful chemical analysis

Scalar Casimir effect between two concentric D-dimensional spheres

The Casimir energy for a massless scalar field between the closely spaced two concentric D-dimensional (for D>3) spheres is calculated by using the mode summation with contour integration in the complex plane of eigenfrequencies and the generalized Abel-Plana formula for evenly spaced eigenfrequency at large argument. The sign of the Casimir energy between closely spaced two concentric D-dimensional spheres for a massless scalar field satisfying the Dirichlet boundary conditions is strictly negative. The Casimir energy between D-1 dimensional surfaces close to each other is regarded as interesting both by itself and as the key to describing of stability of the attractive Casimir force. PACS number(s): 03.70.+k, 11.10.Kk, 11.10.Gh, 03.65.GeComment: 14 pages. arXiv admin note: substantial text overlap with arXiv:1207.418