Quantum-disordered slave-boson theory of underdoped cuprates

We study the stability of the spin gap phase in the U(1) slave-boson theory of the t-J model in connection to the underdoped cuprates. We approach the spin gap phase from the superconducting state and consider the quantum phase transition of the slave-bosons at zero temperature by introducing vortices in the boson superfluid. At finite temperatures, the properties of the bosons are different from those of the strange metal phase and lead to modified gauge field fluctuations. As a result, the spin gap phase can be stabilized in the quantum critical and quantum disordered regime of the boson system. We also show that the regime of quantum disordered bosons with the paired fermions can be regarded as the strong coupling version of the recently proposed nodal liquid theory.Comment: 5 pages, Replaced by the published versio

Disassortativity of random critical branching trees

Random critical branching trees (CBTs) are generated by the multiplicative branching process, where the branching number is determined stochastically, independent of the degree of their ancestor. Here we show analytically that despite this stochastic independence, there exists the degree-degree correlation (DDC) in the CBT and it is disassortative. Moreover, the skeletons of fractal networks, the maximum spanning trees formed by the edge betweenness centrality, behave similarly to the CBT in the DDC. This analytic solution and observation support the argument that the fractal scaling in complex networks originates from the disassortativity in the DDC.Comment: 3 pages, 2 figure

Unionization, Management Adjustment and Productivity

The effect of unionization on productivity is examined in this paper using time-series data on selected establishments in the U.S. cement industry. The analysis combines statistical estimation of the union impact and interviews with union and management officials to forge a link between econometric estimation and the traditional institutional analysis of union policy and management adjustment. The econometric analysis primarily deals with the problem of identifying the impact of the union in the face of firm specific effects and adjustments in labor quality. The case studies are designed to shed light on the question of how unionization affects productivity. The empirical results support the conclusion that unionization leads to productive changes in the operation of the enterprise. Evidence from the case studies suggests that much of the gain in productivity derives from a series of extensive changes in management personnel and procedure. These adjustments are a management response to changes in the employment contract which follow unionization.

Self-organized Model for Modular Complex Networks: Division and Independence

We introduce a minimal network model which generates a modular structure in a self-organized way. To this end, we modify the Barabasi-Albert model into the one evolving under the principle of division and independence as well as growth and preferential attachment (PA). A newly added vertex chooses one of the modules composed of existing vertices, and attaches edges to vertices belonging to that module following the PA rule. When the module size reaches a proper size, the module is divided into two, and a new module is created. The karate club network studied by Zachary is a prototypical example. We find that the model can reproduce successfully the behavior of the hierarchical clustering coefficient of a vertex with degree k, C(k), in good agreement with empirical measurements of real world networks

Large Deviation Function of the Partially Asymmetric Exclusion Process

The large deviation function obtained recently by Derrida and Lebowitz for the totally asymmetric exclusion process is generalized to the partially asymmetric case in the scaling limit. The asymmetry parameter rescales the scaling variable in a simple way. The finite-size corrections to the universal scaling function and the universal cumulant ratio are also obtained to the leading order.Comment: 10 pages, 2 eps figures, minor changes, submitted to PR

Mott physics in 2p2p electron dioxygenyl magnet : O2_{2}MMF6_{6} (MM=Sb, Pt)

We have investigated electronic structures and magnetic properties of O$_{2}$$M$F$_{6}$ ($M$=Sb, Pt), which are composed of two building blocks of strongly correlated electrons: O$_{2}^{+}$ dioxygenyls and $M$F$_{6}^{-}$ octahedra, by employing the first-principles electronic structure band method. For O$_{2}$SbF$_{6}$, as a reference system of O$_{2}$PtF$_{6}$, we have shown that the Coulomb correlation of O(2$p$) electrons drives the Mott insulating state. For O$_{2}$PtF$_{6}$, we have demonstrated that the Mott insulating state is induced by the combined effects of the Coulomb correlation of O(2$p$) and Pt(5$d$) electrons and the spin-orbit (SO) interaction of Pt(5$d$) states. The role of the SO interaction in forming the Mott insulating state of O$_{2}$PtF$_{6}$ is similar to the case of Sr$_{2}$IrO$_{4}$ that is a prototype of a SO induced Mott system with J$_{eff}=1/2$.Comment: 5 pages, 6 figure