Effect of superlattice modulation of electronic parameters on the density of states of cuprate superconductors

Recent scanning tunneling microscopy on BSCCO 2212 has revealed a substantial spatial supermodulation of the energy gap in the superconducting state. We propose that this gap modulation is due to the superlattice modulations of the atoms in the structure, and hence the parameters in a microscopic model of the CuO2 plane. The gap modulation is estimated using renormalized mean field theory for a t- t′ -J model on a superlattice. The results compare well with experiment. © 2007 The American Physical Society.published_or_final_versio

Resonant intrinsic spin hall effect in p-type GaAs quantum well structure

We study intrinsic spin Hall effect in p-type GaAs quantum well structure described by Luttinger Hamiltonian and a Rashba spin-orbit coupling arising from the structural inversion symmetry breaking. The Rashba term induces an energy level crossing in the lowest heavy hole subband, which gives rise to a resonant spin Hall conductance. The resonance may be used to identify the intrinsic spin Hall effect in experiments. © 2006 The American Physical Society.published_or_final_versio

π Junction to probe antiphase s-Wave pairing in iron pnictide superconductors

Josephson junctions between a FeAs-based superconductor with antiphase s-wave pairing and a conventional s-wave superconductor are studied. The translational invariance in a planar junction between a single crystal pnictide and an aluminum metal greatly enhances the relative weight of electron pockets in the pnictide to the critical current. In a wide doping region of the pnictide, a planar and a point contact junction have opposite phases, which can be used to design a trijunction ring with π phase to probe the antiphase pairing. © 2009 The American Physical Society.published_or_final_versio

Quadratic magnetic field dependence of magnetoelectric photocurrent

We experimentally study the spin and electric photocurrents excited by a linearly polarized light via direct interband transitions in an InGaAs/InAlAs quantum well. In the absence of a magnetic field, the linearly polarized light induces a pure spin current due to the spin-orbit coupling, which may be transformed into a measurable electric current by applying an in-plane magnetic field. The induced electric photocurrent is linear with the in-plane magnetic field. Here, we report a quadratic magnetic field dependence of the photocurrent in the presence of an additional perpendicular component of the magnetic field. We attribute the observation to the Hall effect of magnetoelectric photocurrent. © 2011 American Physical Society.published_or_final_versio

Finite-temperature Gutzwiller projection for strongly correlated electron systems

We generalized the Gutzwiller projectional variational method for the ground state of strongly correlated electron systems to the case of finite temperature. Under the Gutzwiller approximation, we show that this maps to a finite temperature renormalized mean-field theory. As one of the key ingredients in the theory, we obtained an explicit expression of the projection entropy or the entropy change due to the projection. We illustrate the application of the theory to the Anderson impurity problem and the half-filled Hubbard model and compare the theory to more elaborate techniques. We find qualitative agreement. The theory can be applied to a wide variety of Hubbard, t-J, and Anderson impurity models. © 2010 The American Physical Society.published_or_final_versio

Magnetoelectric photocurrent generated by direct interband transitions in InGaAs/InAlAs two-dimensional electron gas

We report the observation of magnetoelectric photocurrent generated via direct interband transitions in an InGaAs/InAlAs two-dimensional electron gas by a linearly polarized incident light. The electric current is proportional to the in-plane magnetic field, which unbalances the velocities of the photoexcited carriers with opposite spins and consequently generates the electric current from a hidden spin photocurrent. The spin photocurrent can be evaluated from the measured electric current, and the conversion coefficient of spin photocurrent to electric current is self-consistently estimated to be 10-3-10 -2 per Tesla. The observed light-polarization dependence of the electric current is well explained by a theoretical model which reveals the wave vector angle dependence of the photoexcited carrier density. © 2010 The American Physical Society.published_or_final_versio

Interdependent network reciprocity in evolutionary games

Besides the structure of interactions within networks, also the interactions between networks are of the outmost importance. We therefore study the outcome of the public goods game on two interdependent networks that are connected by means of a utility function, which determines how payoffs on both networks jointly influence the success of players in each individual network. We show that an unbiased coupling allows the spontaneous emergence of interdependent network reciprocity, which is capable to maintain healthy levels of public cooperation even in extremely adverse conditions. The mechanism, however, requires simultaneous formation of correlated cooperator clusters on both networks. If this does not emerge or if the coordination process is disturbed, network reciprocity fails, resulting in the total collapse of cooperation. Network interdependence can thus be exploited effectively to promote cooperation past the limits imposed by isolated networks, but only if the coordination between the interdependent networks is not disturbe

Directional ordering of fluctuations in a two-dimensional compass model

A classical realization of directional coupling in two dimension of the effective orbital-orbital interaction in the Mott insulating phase of the transition metal oxides (TMO) was presented. The model exhibited partial orbital ordering in the form of directional ordering of fluctuation at low temperatures stabilized by an entropy gap. The directional ordering was necessarily accompanied by a lattice distortion and the bond length in horizontal and vertical directions became unequal when the couplings of the orbital isosopin to lattice modes were included. Analysis shows that the compass model has a low temperature phase which exhibited long-ranged correlations in the directions of fluctuations in both isospin and lattice spaces.published_or_final_versio

High volumetric energy density capacitors based on new electrode material lanthanum nitride

This is the author accepted manuscript. The final version is available from the American Chemical Society via the DOI in this recordLaN is synthesized via calcining La2O3 in NH3 and studied as capacitive material for energy storage. A volumetric capacitance of 951.3 F cm-3 was found in 1 mol dm-3 Na2SO4 using a current density of 1 Ag-1, with less than 1% loss of capacitance being experienced after 5000 cycles. In addition, 87.3% of the initial capacitance remained at a current density of 10 A g-1. LaN exhibits high capacitance that is attributed to subsurface space charge accumulation with a possible electric double-layer capacitor component. A reversible electrode process ensures long cycle life and favorable electrical charge transfer. The assembled LaN symmetrical capacitor showed high volumetric energy densities, facilitating high-duty applications.National Natural Science Foundation of ChinaFoundation for Innovation Groups of Basic Research in Gansu Provinc

Automated functional testing of online search services

Search services are the main interface through which people discover information on the Internet. A fundamental challenge in testing search services is the lack of oracles. The sheer volume of data on the Internet prohibits testers from verifying the results. Furthermore, it is difficult to objectively assess the ranking quality because different assessors can have very different opinions on the relevance of a Web page to a query. This paper presents a novel method for automatically testing search services without the need of a human oracle. The experimental findings reveal that some commonly used search engines, including Google, Yahoo!, and Live Search, are not as reliable as what most users would expect. For example, they may fail to find pages that exist in their own repositories, or rank pages in a way that is logically inconsistent. Suggestions are made for search service providers to improve their service quality. Copyright © 2010 John Wiley & Sons, Ltd. A novel method for automatically testing search services without the need of a human oracle is presented. The experimental findings reveal that some commonly used search engines, including Google, Yahoo!, and Live Search, are not as reliable as what most users would expect. For example, they may fail to find pages that exist in their own repositories, or rank pages in a way that is logically inconsistent. Suggestions are made for search service providers to improve their service quality. Copyright © 2010 John Wiley & Sons, Ltd.link_to_subscribed_fulltex