Underscreened Kondo effect in quantum dots coupled to ferromagnetic leads

We analyze the equilibrium transport properties of underscreened Kondo effect in the case of a two-level quantum dot coupled to ferromagnetic leads. Using the numerical renormalization group (NRG) method, we have determined the gate voltage dependence of the dot's spin and level-resolved spectral functions. We have shown that the polarization of the dot is very susceptible to spin imbalance in the leads and changes sign in the middle of the S=1 Coulomb valley. Furthermore, we have also found that by fine-tuning an external magnetic field one can compensate for the presence of ferromagnetic leads and restore the Kondo effect in the case of $S=1/2$ Coulomb valley. However, the underscreened Kondo effect cannot be fully recovered due to its extreme sensitivity with respect to the magnetic field.Comment: 7 pages, 6 figure

Kondo "underscreening" cloud: spin-spin correlations around a partially screened magnetic impurity

We consider the spatial spin correlations around a partially screened spin-1 magnetic moment in a metal exhibiting the underscreened Kondo effect. We find that the underscreening of the impurity spin results in spatial spin correlations that are more pronounced as compared to the fully screened Kondo effect; their power-law decay is weaker because of characteristic logarithmic corrections at large distances. The spin correlator also changes sign as a function of distance to the impurity allowing for ferromagnetic correlations between conduction electron spin density and the local moment. The numerical findings are shown to be in agreement with the predictions deriving from an effective ferromagnetic Kondo Hamiltonian.Comment: 4+ pages, 2 figures, submitted to Phys. Rev.

Kondo screening cloud in a one dimensional wire: Numerical renormalization group study

We study the Kondo model --a magnetic impurity coupled to a one dimensional wire via exchange coupling-- by using Wilson's numerical renormalization group (NRG) technique. By applying an approach similar to which was used to compute the two impurity problem we managed to improve the bad spatial resolution of the numerical renormalization group method. In this way we have calculated the impurity spin - conduction electron spin correlation function which is a measure of the Kondo compensation cloud whose existence has been a long standing problem in solid state physics. We also present results on the temperature dependence of the Kondo correlations.Comment: published versio

Periodicity of high-order functions in the CNS Final progress report, year ending 30 Jun. 1971

Analysis of cerebral slow potentials underlying human attentive processes in central nervous syste

A low-cost mechanism to reconfigure the operating frequency band of a Vivaldi antenna for cognitive radio and spectrum monitoring applications

A frequency agile Vivaldi antenna whose operating frequency band can be switched between two selected bands is proposed in this paper for spectrum monitoring and cognitive radio applications. A RF switch is introduced into the back-slot of a Vivaldi antenna to allow switching of the operational band. The realised gains of the antenna are 10.5 dBi in the low band around 3.1 GHz, and 12 dBi in high band around 4.1 GHz. The radiation pattern is stable and its direction is consistent across the two bands. This design can be applied to multiple reconfigurable bands by using more RF switches to tune the desired operating frequency. A set of reliable design equations has been provided as well. This reconfigurable antenna offers improved gain and isolation over multiple, wideband and multiband antennas without increasing the cost and size when compared to those designs reported

Return to Sexual Activity and Modern Family Planning Use in the Extended Postpartum Period: An Analysis of Findings from Seventeen Countries

Unintended pregnancies can lead to poor maternal and child health outcomes. Family planning use during the first year postpartum has the potential to significantly reduce at least some of these unintended pregnancies. This paper examines the relationship of menses return, breastfeeding status, and postpartum duration on return to sexual activityand use of modern family planning among postpartum women. This paper presents results from a secondary data analysis of Demographic and Health Surveys from 17 countries. For postpartum women, the return of menses,breastfeeding status, and postpartum duration are significantly associated with return to sexual activity in at least 10 out of the 17 countries but not consistently associated with family planning use. Only menses return had a significant association with use of modern family planning in the majority of countries. These findings point to the importance of education about pregnancy risk prior to menses return (Afr J Reprod Health 2010; 14[4]: 75-82)