Local electronic structures on the superconducting interface LaAlO3/SrTiO3LaAlO_{3}/SrTiO_{3}

Motivated by the recent discovery of superconductivity on the heterointerface $LaAlO_{3}/SrTiO_{3}$, we theoretically investigate its local electronic structures near an impurity considering the influence of Rashba-type spin-orbit interaction (RSOI) originated in the lack of inversion symmetry. We find that local density of states near an impurity exhibits the in-gap resonance peaks due to the quasiparticle scattering on the Fermi surface with the reversal sign of the pairing gap caused by the mixed singlet and RSOI-induced triplet superconducting state. We also analyze the evolutions of density of states and local density of states with the weight of triplet pairing component determined by the strength of RSOI, which will be widely observed in thin films of superconductors with surface or interface-induced RSOI, or various noncentrosymmetric superconductors in terms of point contact tunneling and scanning tunneling microscopy, and thus reveal an admixture of the spin singlet and RSOI-induced triplet superconducting states.Comment: Phys. Rev. B 81, 144504 (2010)

Spin-resolved impurity resonance states in electron-doped cuprate superconductors

With the aim at understanding the non-monotonic $d_{x^{2}-y^{2}}$-wave gap, we analyze the local electronic structure near impurities in the electron-doped cuprate superconductors. We find that the local density of states near a non-magnetic impurity in the scenario of $d_{x^{2}-y^{2}}$-wave superconductivity with higher harmonics is qualitatively different from that obtained from the $d_{x^{2}-y^{2}}$-wave superconductivity coexisting with antiferromagnetic spin density wave order. We propose that spin-polarized scanning tunneling microscopy measurements can distinguish the two scenarios and shed light on the real physical origin of a non-monotonic $d_{x^{2}-y^{2}}$-wave gap.Comment: 5 pages, 3 figures, updated version and accepted in Phys. Rev.

Numerical simulations of a ballistic spin interferometer with the Rashba spin-orbital interaction

We numerically investigate the transport behavior of a quasi one-dimension (1D) square loop device containing the Rashba spin-orbital interaction in the presence of a magnetic flux. The conductance versus the magnetic field shows the Al'tshuler-Aronov-Spivak (AAS) and Aharonov-Bohm (AB) oscillations. We focus on the oscillatory amplitudes, and find that both of them are strongly dependent on the spin precession angle (i.e. the strength of the spin-orbit interaction) and exhibit no-periodic oscillations, which are well in agreement with a recent experiment by Koga et al. [cond-mat/0504743(unpublished)]. However, our numerical results for the ideal 1D square loop device for the node positions of the amplitudes of the AB and AAS oscillations are found to be of some discrepancies comparing with quasi-1D square loop with a finite width. In the presence of disorder and taking the disorder ensemble average, the AB oscillation in the conductance will disappear, while the time-reversal symmetric AAS oscillation still remains. Furthermore, the node positions of the AAS oscillatory amplitude remains the same.Comment: 6 pages, 7 figure

Robust and Scalable Distributed Recursive Least Squares

We consider a problem of robust estimation over a network in an errors-in-variables context. Each agent measures noisy samples of a local pair of signals related by a linear regression defined by a common unknown parameter, and the agents must cooperate to find the unknown parameter in presence of uncertainty affecting both the regressor and the regressand variables.We propose a recursive least squares estimation method providing global exponential convergence to the unknown parameter in absence of uncertainty, and robust stability of the estimate, formalized in terms of input-to-state stability, in presence of uncertainty affecting all the variables. The result relies on a cooperative excitation assumption that is proved to be strictly weaker than persistency of excitation of each local data set. The proposed estimator is validated on an adaptive road pricing application

Deduction of Pure Spin Current from Spin Linear and Circular Photogalvanic Effect in Semiconductor Quantum Wells

We study the spin photogalvanic effect in two-dimensional electron system with structure inversion asymmetry by means of the solution of semiconductor optical Bloch equations. It is shown that a linearly polarized light may inject a pure spin current in spin-splitting conduction bands due to Rashba spin-orbit coupling, while a circularly polarized light may inject spin-dependent photocurrent. We establish an explicit relation between the photocurrent by oblique incidence of a circularly polarized light and the pure spin current by normal incidence of a linearly polarized light such that we can deduce the amplitude of spin current from the measured spin photocurrent experimentally. This method may provide a source of spin current to study spin transport in semiconductors quantitatively

Enhanced gradient tracking algorithms for distributed quadratic optimization via sparse gain design

In this paper we propose a new control-oriented design technique to enhance the algorithmic performance of the distributed gradient tracking algorithm. We focus on a scenario in which agents in a network aim to cooperatively minimize the sum of convex, quadratic cost functions depending on a common decision variable. By leveraging a recent system-theoretical reinterpretation of the considered algorithmic framework as a closed-loop linear dynamical system, the proposed approach generalizes the diagonal gain structure associated to the existing gradient tracking algorithms. Specifically, we look for closed-loop gain matrices that satisfy the sparsity constraints imposed by the network topology, without however being necessarily diagonal, as in existing gradient tracking schemes. We propose a novel procedure to compute stabilizing sparse gain matrices by solving a set of nonlinear matrix inequalities, based on the solution of a sequence of approximate linear versions of such inequalities. Numerical simulations are presented showing the enhanced performance of the proposed design compared to existing gradient tracking algorithms

Impurity resonance states in noncentrosymmetric superconductor CePt3SiCePt_{3}Si: a probe for Cooper-pairing symmetry

Motivated by the recent discovery of noncentrosymmetric superconductors, such as $CePt_{3}Si$, $CeRhSi_{3}$ and $CeIrSi_{3}$, we investigate theoretically the impurity resonance states with coexisting $s$- and p-wave pairing symmetries. Due to the nodal structure of the gap function, we find single nonmagnetic impurity-induced resonances appearing in the local density of state (LDOS). In particular, we analyze the evolution of the local density of states for coexisting isotropic s-wave and p-wave superconducting states and compare with that of anisotropic s-wave and p-wave symmetries of the superconducting gap. Our results show that the scanning tunneling microscopy can shed light on the particular structure of the superconducting gap in non-centrosymmetric superconductors.Comment: 5 pages, 5 figures, typos corrected, final version in Phys. Rev.

D-branes as GMS Solitons in Vacuum String Field Theory

In this paper we map the D-brane projector states in the vacuum string field theory to the noncommutative GMS solitons based on the recently proposed map of Witten's star to Moyal's star. We find that the singular geometry conditions of Moore and Taylor are associated with the commutative modes of these projector states in our framework. The properties of the candidate closed string state and the wedge state are also discussed, and the possibility of the non-GMS soliton in VSFT is commented.Comment: 19 pages, LaTex; revised version, typos corrected; third version, a new subsection about the midpoint singulariy regularization added;fourth edition, arguments improve

Incorporating basic calibrations in existing machine-learned turbulence modeling

This work aims to incorporate basic calibrations of Reynolds-averaged Navier-Stokes (RANS) models as part of machine learning (ML) frameworks. The ML frameworks considered are tensor-basis neural network (TBNN), physics-informed machine learning (PIML), and field inversion & machine learning (FIML) in J. Fluid Mech., 2016, 807, 155-166, Phys. Rev. Fluids, 2017, 2(3), 034603 and J. Comp. Phys., 2016, 305, 758-774, and the baseline RANS models are the one-equation Spalart-Allmaras model, the two-equation $k$-$\omega$ model, and the seven-equation Reynolds stress transport models. ML frameworks are trained against plane channel flow and shear-layer flow data. We compare the ML frameworks and study whether the machine-learned augmentations are detrimental outside the training set. The findings are summarized as follows. The augmentations due to TBNN are detrimental. PIML leads to augmentations that are beneficial inside the training dataset but detrimental outside it. These results are not affected by the baseline RANS model. FIML's augmentations to the two eddy viscosity models, where an inner-layer treatment already exists, are largely neutral. Its augmentation to the seven-equation model, where an inner-layer treatment does not exist, improves the mean flow prediction in a channel. Furthermore, these FIML augmentations are mostly non-detrimental outside the training dataset. In addition to reporting these results, the paper offers physical explanations of the results. Last, we note that the conclusions drawn here are confined to the ML frameworks and the flows considered in this study. More detailed comparative studies and validation & verification studies are needed to account for developments in recent years

Acceleration of bouncing balls in external fields

We introduce two models, the Fermi-Ulam model in an external field and a one dimensional system of bouncing balls in an external field above a periodically oscillating plate. For both models we investigate the possibility of unbounded motion. In a special case the two models are equivalent