Interface roughness and proximity effect on a c-axis Josephson junction between s-wave and d-wave superconductors

The scanning superconducting quantum interference device microscope on tri-crystal high-temperature superconductor (HTSC) samples unambiguously identifies the d-wave pairing symmetry as a predominant component. This fact was also seen clearly from the current phase relation (CPR) for an in-plane junction between HTSC's, where both π periodicity and 2π periodicity are observed, depending on the relative crystal orientation. However, for c-axis junctions between HTSC's and conventional superconductor, ac Josephson effect shows that the main Shapino steps occur at V=nhf/2e (n is integer) and thus a significant s-wave component is indicated. To understand the experimental measurements, we have studied interface roughness and proximity effect on CPR of such junctions. The order parameter profiles and current phase relation are computed self-consistently using the quasiclassical theory and rough interface model. Our results suggest that the existence of a minor surface s-wave component stemming from a repulsive s-channel pairing potential in the d-wave superconductor is able to give a coherent picture.published_or_final_versio

Order parameters and current-phase relations in 3He-B Josephson junctions through a porous layer

Recent discoveries of the π states in 3He-B Josephson junctions through an array of apertures and a single aperture have aroused much theoretical interest on the mechanism of π states. Both tunneling junction and single orifice junction models were successfully applied to explain the occurrence of π states and their relationship with the texture orientations of n̂ vectors in two 3He-B reservoirs. In this paper, we study a model 3He-B Josephson junction through a porous layer. The order parameters and current-phase relations are calculated self-consistently using the quasiclassical theory. In agreement with previous theories, the π state is also observed when the n̂'s are aligned antiparallel and normal to the porous layer. In this model, however, the π state exists only when the coupling between two 3He-B reservoirs is strong, and the usual 0 state is present when the coupling diminishes. Being contrary to the single aperture case, the π state in our model is robust only when the magnetic field is aligned either nearly normal to or within the porous layer.published_or_final_versio

Effect of a point impurity on the vortex bound states in an s-wave superconductor: A self-consistent analysis

On the basis of self-consistent numerical solution of the Bogoliubov-de Gennes equations on a finite-size lattice, we study the variation of the vortex bound state when an impurity potential is added to the core of an isolated vortex line in an s-wave superconductor. The local density of states is investigated at both the core and its neighbor site. By analyzing the impurity-induced increase of the pair potential near the vortex core, we elucidate the mechanism of the vortex pinning in detail.published_or_final_versio

Order parameter and current-phase relation in Josephson junctions composed of g+s-wave superconductors

Based on the analyses of bulk sensitive experimental data on penetration depths, Raman spectra, electron photoemission spectra, etc., G. M. Zhao concluded in a recent paper [Phys. Rev. B 64, 024503 (2001)] that the symmetry of high-Tc superconductors belongs to the g+s-wave type. To explore the common and uncommon features of the g+s-wave pairing state with respect to the d-wave pairing state, both superconductor-insulator-superconductor junction and superconductor-normal metal-superconductor junction have been studied self-consistently in this paper using the quasiclassical theory. The current phase relation for g+s-wave superconductors Δ(s,θ)=Δ0(s+cos 4θ) is investigated systematically as functions of s-wave component, crystal orientation angle β, as well as roughness ρ of the interface layer. Our results show that there exists a critical βC for a given s and ρ so that the current phase relation approaches asymptotically to I(φ)=ICsin(2φ) from I(φ)=ICsin(φ) as β→βC. The order parameter and βC-s relation are calculated self-consistently as interface roughness varies. Our results are compared with their counterparts in Josephson junctions with the d-wave pairing state obtained using a similar method.published_or_final_versio

Electronic structure of the vortex lattice of d-, d+is-, and dx2-y2+idxy-wave superconductors

On the basis of the self-consistent Bogoliubov-de Gennes equations and a tight-binding lattice model, we investigate the quasiparticle spectrum of vortex-lattice state in pure d-, mixed d+is, and dx2-y2+idxy-wave superconductors. For a d-wave case, the local density of states (LDOS) at the vortex core shows a multipeak structure, and the positions of peaks as well as the width of splitting between peaks are sensitively dependent on both the magnetic-field strength and the orientation of the vortex lattice. For the mixed d+is- and dx2-y2+idxy-wave pairing states, we observe a double-peak structure of the local density of states at vortex center, where the two peaks are asymmetrically situated around the Fermi energy. By taking into account the matrix-element effect, the local density of states appears to be qualitatively consistent with the scanning-tunneling-microscopy experimental data.published_or_final_versio

Intermediate spin state stabilized by the Jahn-Teller distortion in La1/2Ba1/2CoO3

The recent high-resolution neutron and synchrotron diffraction measurements by Fauth et al. [Phys. Rev. B 65, 060401(R) (2002)] demonstrated the existence of an intermediate spin state in half-doped La1/2Ba1/2CoO3 which is accompanied by a long-range tetragonal Jahn-Teller distortion. In this paper we find that the charge uniform ferromagnetic intermediate spin state strongly couples to the Jahn-Teller effect and is stable only at moderate distortion of 1%. While the calculated magnetic moment of this state is in agreement with the experimentally measured one, the corresponding orbital ordering is the nearest-neighboring alternating d3x2-r2/d3y2-r2, instead of the observed uniform d3z2-r2 orbital ordering. A calculation is carried out using the self-consistent unrestricted Hartree-Fock approximation on a realistic multiband d-p Hubbard Hamiltonian and a generalized Jahn-Teller coupling model, in which all possible spin-, charge-, and orbital-ordered states are considered.published_or_final_versio

Holonomic quantum computation using rf superconducting quantum interference devices coupled through a microwave cavity

We propose a different scheme to realize holonomic quantum computation with rf superconducting quantum interference device (SQUID) qubits in a microwave cavity. In this scheme associated with the non-Abelian holonomies, the single-qubit gates and a two-qubit controlled-PHASE gate as well as a controlled-NOT gate can be easily constructed by tuning adiabatically the Rabi frequencies of classical microwave pulses coupled to the SQUIDs. The fidelity of these gates is estimated to be possibly higher than 90% with the current technology. © 2005 The American Physical Society.published_or_final_versio

Dominant bidding strategy in Mobile App advertising auction

The widespread use of intelligent mobile phone has promoted prosperity of mobile App advertising in recent years. Based on existing bidding status, this paper presents the dominant bidding strategy for mobile advertising auction. Firstly, our study characterizes multiple Nash Equilibria resulting from different bidding strategies in wGSP (weighted Generalized Second-Price) auction. Further more, we prove that advertiser’s rank and utility will not decrease by using the dominant bidding strategy. We also consider the situation where the reserve price is set by the mobile advertising platform. It turns out that that advertiser’s payment will be no less than reserve price. Finally, a practical implementation for a virtual market simulates the dynamic bidding process in real world environments.published_or_final_versio

Macroscopic Klein tunneling in spin-orbit-coupled Bose-Einstein condensates

We propose an experimental scheme to detect macroscopic Klein tunneling with spin-orbit-coupled Bose-Einstein condensates (BECs). We show that a nonlinear Dirac equation with tunable parameters can be realized with such BECs. Through numerical calculations, we demonstrate that macroscopic Klein tunneling can be clearly detected under realistic conditions. Macroscopic quantum coherence in such relativistic tunneling is clarified and a BEC with a negative energy is shown to be able to transmit transparently through a wide Gaussian potential barrier. © 2012 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