s-wave Cooper pair insulators and theory of correlated superconductors

The pseudogap state of cuprate high-temperature superconductors has been often viewed as either a yet unknown competing order or a precursor state to superconductivity. While awaiting the resolution of the pseudogap problem in cuprates, we demonstrate that local pairing fluctuations, vortex liquid dynamics and other precursor phenomena can emerge quite generally whenever fermionic excitations remain gapped across the superconducting transition, regardless of the gap origin. Our choice of a tractable model is a lattice band insulator with short-range attractive interactions between fermions in the s-wave channel. An effective crossover between Bardeen-Cooper-Schrieffer (BCS) and Bose-Einstein condensate (BEC) regimes can be identified in any band insulator above two dimensions, while in two dimensions only the BEC regime exists. The superconducting transition is "unconventional" (non-pair-breaking) in the BEC regime, identified by either the bosonic mean-field or XY universality class. The insulator adjacent to the superconductor in the BEC regime is a bosonic Mott insulator of Cooper pairs, which may be susceptible to charge density wave ordering. We construct a function of the many-body excitation spectrum whose non-analytic changes define a sharp distinction between band and Mott insulators. The corresponding "second order transition" can be observed out of equilibrium by driving a Cooper pair laser in the Mott insulator. We explicitly show that the gap for charged bosonic excitations lies below the threshold for Cooper pair breakup in any BEC regime, despite quantum fluctuations. Our discussion ends with a view of possible consequences for cuprates, where antinodal pair dynamics has certain features in common with our simple s-wave picture.Comment: 18 pages, 4 figures, published versio

Extrinsic Entwined with Intrinsic Spin Hall Effect in Disordered Mesoscopic Bars

We show that pure spin Hall current, flowing out of a four-terminal phase-coherent two-dimensional electron gas (2DEG) within inversion asymmetric semiconductor heterostructure, contains contributions from both the extrinsic mechanisms (spin-orbit dependent scattering off impurities) and the intrinsic ones (due to the Rashba coupling). While the extrinsic contribution vanishes in the weakly and strongly disordered limits, and the intrinsic one dominates in the quasiballistic limit, in the crossover transport regime the spin Hall conductance, exhibiting sample-to-sample large fluctuations and sign change, is not simply reducible to either of the two mechanisms, which can be relevant for interpretation of experiments on dirty 2DEGs [V. Sih et al., Nature Phys. 1, 31 (2005)].Comment: 5 pages, 3 color EPS figure

Quest for Rare Events in three-dimensional Mesoscopic Disordered Metals

The study reports on the first large statistics numerical experiment searching for rare eigenstates of anomalously high amplitudes in three-dimensional diffusive metallic conductors. Only a small fraction of a huge number of investigated eigenfunctions generates the far asymptotic tail of their amplitude distribution function. The relevance of the relationship between disorder and spectral averaging, as well as of the quantum transport properties of the investigated mesoscopic samples, for the numerical exploration of eigenstate statistics is divulged. The quest provides exact results to serve as a reference point in understanding the limits of approximations employed in different analytical predictions, and thereby the physics (quantum vs semiclassical) behind large deviations from the universal predictions of random matrix theory.Comment: 5 pages, 3 embedded EPS figures, figure 3 replaced with new findings on spectral vs disorder averagin

Structural, chemical and deformation changes in friction welded joint of dissimilar steels

Fundamental principles of friction welding of dissimilar steels (high speed and tempering steel) from the aspect of metallurgical and chemical processes occurring in the joint zone are presented in this paper. Considering that phenomena accompanying the friction welding are interdependent, it was necessary to experimentally determine the process variable parameters, to establish the optimal welding regime. The experiments were set and realized so that all the variables were analyzed as a function of the friction time. The metallographic investigations included analysis of the joint zone microstructure through structural phases and hardness changes, due to influence of the heat treatment - annealing. The experimental work included analysis of the geometry changes, the joint zone structure and the basic mechanical characteristics of the joint realized by the friction welding

Spin Hall Current Driven by Quantum Interferences in Mesoscopic Rashba Rings

We propose an all-electrical nanoscopic structure where {\em pure} spin current is induced in the transverse voltage probes attached to {\em quantum-coherent} one-dimensional ring when conventional unpolarized charge current is injected through its longitudinal leads. Tuning of the Rashba spin-orbit coupling in semiconductor heterostructure hosting the ring generates quasi-periodic oscillations of the predicted spin Hall current due to {\em spin-sensitive quantum-interference effects} caused by the difference in Aharonov-Casher phase acquired by opposite spins states traveling clockwise and counterclockwise. Its amplitude is comparable to the mesoscopic spin Hall current predicted for finite-size two-dimensional electron gases, while it gets reduced in wide two-dimensional or disordered rings.Comment: 5 pages, 4 color figure

Optimizing the speed of a Josephson junction

We review the application of dynamical mean-field theory to Josephson junctions and study how to maximize the characteristic voltage IcRn which determines the width of a rapid single flux quantum pulse, and thereby the operating speed in digital electronics. We study a wide class of junctions ranging from SNS, SCmS (where Cm stands for correlated metal), SINIS (where the insulating layer is formed from a screened dipole layer), and SNSNS structures. Our review is focused on a survey of the physical results; the formalism has been developed elsewhere.Comment: (36 pages, 15 figures, to appear in Int. J. Mod. Phys. B

Transverse Spin-Orbit Force in the Spin Hall Effect in Ballistic Semiconductor Wires

We introduce the spin and momentum dependent {\em force operator} which is defined by the Hamiltonian of a {\em clean} semiconductor quantum wire with homogeneous Rashba spin-orbit (SO) coupling attached to two ideal (i.e., free of spin and charge interactions) leads. Its expectation value in the spin-polarized electronic wave packet injected through the leads explains why the center of the packet gets deflected in the transverse direction. Moreover, the corresponding {\em spin density} will be dragged along the transverse direction to generate an out-of-plane spin accumulation of opposite signs on the lateral edges of the wire, as expected in the phenomenology of the spin Hall effect, when spin-$\uparrow$ and spin-$\downarrow$ polarized packets (mimicking the injection of conventional unpolarized charge current) propagate simultaneously through the wire. We also demonstrate that spin coherence of the injected spin-polarized wave packet will gradually diminish (thereby diminishing the ``force'') along the SO coupled wire due to the entanglement of spin and orbital degrees of freedom of a single electron, even in the absence of any impurity scattering.Comment: 5 pages, 4 color EPS figures; 2 new figures and expanded discussion on the sign of spin Hall quantities. To appear in Phys. Rev. B 72 (2005

Mesoscopic Spin Hall Effect in Multiprobe Ballistic Spin-Orbit Coupled Semiconductor Bridges

We predict that unpolarized charge current driven through the longitudinal leads attached to ballistic quantum-coherent two-dimensional electron gas (2DEG) in semiconductor heterostructure will induce a {\em pure} spin current, which is not accompanied by any net charge flow, in the transverse voltage probes. Its magnitude can be tuned by the Rashba spin-orbit (SO) interaction and, moreover, it is resilient to weak spin-independent scattering off impurities within the metallic diffusive regime. While the polarization vector of the spin transported through the transverse leads is not orthogonal to the plane of 2DEG, we demonstrate that only two components (out-of-plane and longitudinal) of the transverse spin current are signatures of the spin Hall effect in four-probe Rashba spin-split semiconductor nanostructures. The linear response spin Hall current, obtained from the multiprobe Landauer-B\" uttiker scattering formalism generalized for quantum transport of spin, is the Fermi-surface determined nonequilibrium quantity whose scaling with the 2DEG size $L$ reveals the importance of processes occurring on the spin precession {\em mesoscale} $L_{\rm SO}$ (on which spin precesses by an angle $\pi$)--the out-of-plane component of the transverse spin current exhibits quasioscillatory behavior for $L \lesssim L_{\rm SO}$ (attaining the maximum value in 2DEGs of the size $L_{\rm SO} \times L_{\rm SO}$), while it reaches the asymptotic value in the macroscopic regime $L \gg L_{\rm SO}$. Furthermore, these values of the spin Hall current can be manipulated by the measuring geometry defined by the attached leads.Comment: 12 pages, 6 color EPS figures; expanded discussion to emphasize crucial role played by processes on the spin precession mesoscal

Immunoreactive neuropeptides in the cells of human thymus

The study was designed to explore the expression of different neuropeptides, viz. vasoactive intestinal peptide (VIP), calcitonin gene related peptide (CGRP), substance P (SP), bombesin and motilin in the cells of fetal and adult human thymus. Immunohistochemical staining revealed that cortical and medullary thymocytes were labeled by all antibodies, except those specific for motilin. Immunoreactive VIP and SP were observed in the solitary epithelial cells located in the subcapsular/subtrabecular cortex, at the corticomedullary junction and in the medulla. The cells within the subcapsular/subtrabecular monolayer, rare solitary cells in the deep cortex and epithelial cell network in the medulla, were labeled with antibodies to CGRP and bombesin. Hassall's corpuscles were labeled with all antibodies except that specific for SP. The obtained data obtained testify to the expression of different neuropeptides in human thymic lymphoid and non-lymphoid cells and suggest a role for neuroendocrine hormone-mediated mechanisms in the regulation of thymic homeostasis in humans

Universal conductance fluctuations in non-integer dimensions

We propose an Ansatz for Universal conductance fluctuations in continuous dimensions from 0 up to 4. The Ansatz agrees with known formulas for integer dimensions 1, 2 and 3, both for hard wall and periodic boundary conditions. The method is based solely on the knowledge of energy spectrum and standard assumptions. We also study numerically the conductance fluctuations in 4D Anderson model, depending on system size L and disorder W. We find a small plateau with a value diverging logarithmically with increasing L. Universality gets lost just in 4D.Comment: 4 pages, 4 figures submitted to Phys. Rev.