The microscopic basis for phase-sensitive experiments for determination of the order parameter symmetry in Fe-based superconductors

We present a microscopic theory of dc Josephson current, based on the construction of a coherent temperature Green function in the tight-binding approximation, in junctions with multiband superconductors. This theory is applied to the junctions with multiband Fe-based superconductors (FeBS) described by anisotropic s-wave order parameter symmetries, which probably realized in FeBS. We confirm microscopically the previously suggested crucial experiment for determination of the type of the order parameter symmetry in FeBS.Comment: 5 pages, 3 figure

Anomalous superconducting proximity effect and coherent charge transport in semiconducting thin film with spin-orbit interaction

We present a microscopic theory of the superconducting proximity effect in a semiconducting thin film with spin-orbit interaction ($N_{SO}$) in an external magnetic field. We demonstrate that an effective 1D Hamiltonian which describes induced superconductivity in $N_{SO}$ in contact with a usual $s$-wave superconductor possesses not only spin-singlet induced superconducting order parameter term, as commonly adopted, but spin triplet order parameter term also. Using this new effective Hamiltonian we confirm previous results for a normal current across contacts of $N_{SO}$ with a normal metal and for a Josephson current with the same $N_{SO}$ with induced superconductivity, obtained previously in the framework of the phenomenological Hamiltonian without spin-triplet terms. However, a calculated current-phase relation across the transparent contact between $N_{SO}$ with induced superconductivity in magnetic field and usual $s$-wave superconductor differs significantly from previous results. We suggest the experiment which can confirm our theoretical predictions.Comment: 5 pages, 6 figure

Magnetism, superconductivity and coupling in cuprate heterostructures probed by low-energy muon-spin rotation

We present a low-energy muon-spin-rotation study of the magnetic and superconducting properties of YBa2Cu3O7/PrBa2Cu3O7 trilayer and bilayer heterostructures. By determining the magnetic-field profiles throughout these structures we show that a finite superfluid density can be induced in otherwise semiconducting PrBa2Cu3O7 layers when juxtaposed to YBa2Cu3O7 "electrodes" while the intrinsic antiferromagnetic order is unaffected.Comment: 10 pages, 9 figures; figure 9 corrected in version

Steps on current-voltage characteristics of a silicon quantum dot covered by natural oxide

Considering a double-barrier structure formed by a silicon quantum dot covered by natural oxide with two metallic terminals, we derive simple conditions for a step-like voltage-current curve. Due to standard chemical properties, doping phosphorus atoms located in a certain domain of the dot form geometrically parallel current channels. The height of the current step typically equals to (1.2 pA)N, where N=0,1,2,3... is the number of doping atoms inside the domain, and only negligibly depends on the actual position of the dopants. The found conditions are feasible in experimentally available structures.Comment: 4 pages, 3 figure

The Josephson current in Fe-based superconducting junctions: theory and experiment

We present theory of dc Josephson effect in contacts between Fe-based and spin-singlet $s$-wave superconductors. The method is based on the calculation of temperature Green's function in the junction within the tight-binding model. We calculate the phase dependencies of the Josephson current for different orientations of the junction relative to the crystallographic axes of Fe-based superconductor. Further, we consider the dependence of the Josephson current on the thickness of an insulating layer and on temperature. Experimental data for PbIn/Ba$_{1-x}$K$_{x}$(FeAs)$_2$ point-contact Josephson junctions are consistent with theoretical predictions for $s_{\pm}$ symmetry of an order parameter in this material. The proposed method can be further applied to calculations of the dc Josephson current in contacts with other new unconventional multiorbital superconductors, such as $Sr_2RuO_4$ and superconducting topological insulator $Cu_xBi_2Se_3$.Comment: 16 pages, 14 figure

Heteronuclear compounds formed in the systems based on Fe(II), Fe(III), Al(III), SO 4 2-, Cl--H2O-OH -, and NH3

The possibility of synthesizing heteronuclear compounds in the systems based on Fe(II), Fe(III), Al(III), SO 4 2-, Cl --H2O-OH-, and NH3 was studied. A mathematical model based on data on the potentiometric titration was developed. The elemental and phase composition and the structure of the compounds synthesized were determined by the XPA, DTA and NMR methods to optimize the conditions of the synthesis. © 2010 Pleiades Publishing, Ltd

Evaluation of the regulatory effect of carnosine and alpha-lipoic acid on the cytokine profile of the cerebral cortex of Wistar rats under induced obesity

BACKGROUND: The model of obesity under experimental conditions is reproduced by using high-calorie diets in animals. It has been established that metabolic disorders cause meta-inflammation not only in peripheral organs and tissues, but also in brain structures. The search for effective neuroprotective antioxidants to suppress inflammatory processes in the cerebral cortex in obesity is an urgent task due to the widespread prevalence of this disease.AIM: to evaluate the effect of minor biologically active substances — carnosine (CAR) and α-lipoic acid (ALA) on the cytokine profile of the frontal cortex of the left hemisphere of the brain in Wistar male rats with obesity induced by a high-calorie choline-deficient diet.MATERIALS AND METHODS: The studies were carried out on male Wistar rats with an initial body weight of 150±10 g. The animals were randomized by body weight into 5 groups. For 8 weeks, rats of the 1st (control) group received a complete modified diet of AIN93M; rats of the 2nd group consumed a high-calorie choline-deficient diet (HCHDR), the fat content of which was 45%, fructose — 20% of the energy value of the diet; rats of the 3rd group received HCHDR with the addition of CAR at a dose of 75 mg per 1 kg of body weight; rats of the 4th group received HCHDR with the addition of ALA at a dose of 75 mg per 1 kg of body weight; rats of the 5th group received HCHDR with the addition of the CAR + ALA complex in a total dose of 150 mg per 1 kg of body weight. Animals were removed from the experiment by decapitation under ether anesthesia. The levels of triglycerides (Tg) and free fatty acids (FFA) in blood plasma (mmol) were determined on a biochemical analyzer (Konelab 20i, Thermo Clinical Labsystems Oy, Finland). Content of cytokines and chemokines (pg/ml): GM-CSF, IL-10, IL-17A, IL-12p40, IL-12p70, IL-1α, IL-2, IL-4, IL-5, IFN-γ, MCP-1, M-CSF, MIP-1α, MIP-2, MIP-3α, RANTES, and TNF-α in cerebral cortex lysates were determined by multiplex immunoassay using a Luminex 200 analyzer (Luminex Corporation, USA). To assess the relationship between the level of cytokines in blood plasma and changes in their concentrations under the influence of HCCDR in lysates of the cortex of the frontal lobe of the left hemisphere of the brain, the ratio was calculated: the level of cytokines pg/ml in blood plasma [1]/the content of cytokines pg/ml in lysates (pl/ lys) for each sample.RESULTS: On the model of obesity in rats, the presence of an inflammatory process in the cerebral cortex was established, as evidenced by an increase in the content of pro-inflammatory factors: IL-2, M-CSF, MIP-1α and RANTES and a decrease in the content of immunoregulatory cytokines of varying severity: IL-10, IL17A, IL-12p40, IL-12p70, TNF-a, MIP-2 and MIP-3α in group 2 rats. (HCHDR) compared with the control group. Enrichment of HCHDR with biologically active substances: CAR, ALA or their complex, ensured the normalization of lipid metabolism, as evidenced by the decrease in the ratio of circulating Tg to FFA in the blood serum of rats to control values: 1st gr. (control) — 1,04±0.23; 2nd gr. (HCHDR) — 1,64±0.63; 3rd gr. (CAR) — 0,98±0.31; 4th gr. (ALA) — 0,86±0.31; 5th gr. (CAR+ALA) — 1,02±0.38. Enrichment of HCHDR with CAR, ALA or their complex led to a decrease in the content of pro-inflammatory and apoptosis-regulating cytokines and chemokines in the cortex of the frontal lobe of the rat brain: IL-1α, IL-2, IL-17A, M-CSF, MCP-1, MIP3α and RANTES, along with an increase in the level of the anti-inflammatory cytokine IL-10, which indicates the suppression of the inflammatory process induced by the consumption of HCHDR in rats.CONCLUSION: The data obtained indicate the prospect of using CAR and ALA or their complex as neuroprotective antioxidants to reduce the inflammatory process in brain structures in obesity

The Anderson Model out of equilibrium: Time dependent perturbations

The influence of high-frequency fields on quantum transport through a quantum dot is studied in the low-temperature regime. We generalize the non crossing approximation for the infinite-U Anderson model to the time-dependent case. The dc spectral density shows asymmetric Kondo side peaks due to photon-assisted resonant tunneling. As a consequence we predict an electron-photon pump at zero bias which is purely based on the Kondo effect. In contrast to the resonant level model and the time-independent case we observe asymmetric peak amplitudes in the Coulomb oscillations and the differential conductance versus bias voltage shows resonant side peaks with a width much smaller than the tunneling rate. All the effects might be used to clarify the question whether quantum dots indeed show the Kondo effect.Comment: 13 pages, REVTEX 3.0, 5 figure