A simple interpretation of quantum mirages

In an interesting new experiment the electronic structure of a magnetic atom adsorbed on the surface of Cu(111), observed by STM, was projected into a remote location on the same surface. The purpose of the present paper is to interpret this experiment with a model Hamiltonian, using ellipses of the size of the experimental ones, containing about 2300 atoms. The charge distribution for the different wavefunctions is analyzed, in particular, for those with energy close to the Fermi energy of copper Ef. Some of them show two symmetric maxima located on the principal axis of the ellipse but not necessarily at the foci. If a Co atom is adsorbed at the site where the wavefunction with energy $E_F$ has a maximum and the interaction is small, the main effect of the adsorbed atom will be to split this particular wavefunction in two. The total charge density will remain the same but the local density of states will present a dip at Ef at any site where the charge density is large enough. We relate the presence of this dip to the observation of quantum mirages. Our interpretation suggests that other sites, apart from the foci of the ellipses, can be used for projecting atomic images and also indicates the conditions for other non magnetic adsorbates to produce mirages.Comment: 3 pages, 3 Fig

Nanoscale Impurity Structures on the Surface of dx2−y2d_{x^2-y^2}-wave Superconductors

We study the effects of nanoscale impurity structures on the local electronic structure of $d_{x^2-y^2}$-wave superconductors. We show that the interplay between the momentum dependence of the superconducting gap, the geometry of the nanostructure and its orientation gives rise to a series of interesting quantum effects. Among these are the emergence of a zero bias conductance peak in the superconductor's density of states and the suppression of impurity states for certain nanostructures. The latter effect can be used to screen impurity resonances in the superconducting state.Comment: 4 pages, 5 figure

Adsorbed 3d transition metal atoms and clusters on Au(111):Signatures derived from one electron calculations

The spectroscopic characteristics of systems with adsorbed d impurities on noble metal surfaces should depend on the number and geometric arrangement of the adsorbed atoms and also on their d band filling. Recent experiments using scanning tunneling microscopy have probed the electronic structure of all 3d transition metal impurities and also of Co dimers adsorbed on Au(111), providing a rich variety of results. In this contribution we correlate those experimental results with ab-initio calculations and try to establish necessary conditions for observing a Kondo resonance when using the single impurity Anderson model. We find that the relevant orbitals at the STM tip position, when it is on top of an impurity, are the dThe spectroscopic characteristics of systems with adsorbed d impurities on noble metal surfaces should depend on the number and geometric arrangement of the adsorbed atoms and also on their d band filling. Recent experiments using scanning tunneling microscopy have probed the electronic structure of all 3d transition metal impurities and also of Co dimers adsorbed on Au(111), providing a rich variety of results. In this contribution we correlate those experimental results with ab-initio calculations and try to establish necessary conditions for observing a Kondo resonance when using the single impurity Anderson model. We find that the relevant orbitals at the STM tip position, when it is on top of an impurity, are the d orbitals with m=0 and that the energy of these levels with respect to the Fermi energy determines the possibility of observing a spectroscopic feature due to the impurity. orbitals with m=0 and that the energy of these levels with respect to the Fermi energy determines the possibility of observing a spectroscopic feature due to the impurity

Aspekte der Mast- und Schlachtleistung sowie Wirtschaftlichkeit von Schweinen bei 100% Biofütterung

In an organic fattening trial 62 pigs of the genotype (PixHa)x(DuxGLR) were divided into 2 groups which were fed during finishing period with a ration containing soy prod-ucts or farm grown grain legumes, respectively. The Methionin deficit of the second group did not affect negatively the fattening performance, whereas lean meat content decreased significantly. In spite of lower feed costs of the second group the profitabil-ity was lower

Impurities, Quantum Interference and Quantum Phase Transitions in s-wave superconductors

We study the effects of quantum interference in impurity structures consisting of two or three magnetic impurities that are located on the surface of an s-wave superconductor. By using a self-consistent Bogoliubov-de Gennes formalism, we show that quantum interference leads to characteristic signatures not only in the local density of states (LDOS), but also in the spatial form of the superconducting order parameter. We demonstrate that the signatures of quantum interference in the LDOS are qualitatively, and to a large extent quantitatively unaffected by the suppression of the superconducting order parameter near impurities, which illustrates the robustness of quantum interference phenomena. Moreover, we show that by changing the interimpurity distance, or the impurities' scattering strength, the s-wave superconductor can be tuned through a series of first order quantum phase transitions in which the spin polarization of its ground state changes. In contrast to the single impurity case, this transition is not necessarily accompanied by a $\pi$-phase shift of the order parameter, and can in certain cases even lead to its enhancement. Our results demonstrate that the superconductor's LDOS, its spin state, and the spatial form of the superconducting order parameter are determined by a subtle interplay between the relative positions of the impurities and their scattering strength

Criteris d'avaluació pels centres que participen al programa agenda 21 escolar de Barcelona. Anàlisi d'un instrument d'autoavaluació i respostes davant la proposta de la seva implementació

L'Agenda 21 Escolar de Barcelona és un programa adreçat als centres de totes les etapes educatives. Un programa d'educació, participació i implicació cívica, que actua com a estímul i suport a la introducció de criteris de sostenibilitat. Això significa que de manera progressiva, el centre es va implicant en la revisió i transformació de les pràctiques escolars, assegurant la participació real dels protagonistes, creant espais i condicions per actuar amb autonomia, responsabilitat, cooperació ... Al finalitzar el cinquè curs d'A21E, els centres poden iniciar una nova etapa fent una memòria del quinquenni. El treball descriu una eina d'autoavaluació elaborada en el marc d'un grup de treball constituït per la coordinació del programa i professorat de centres diversos i l'anàlisi de les respostes dels claustres a l'hora de rebre la proposta i d'utilitzar l'instrument

Criteris d’avaluació pels centres que participen al programa agenda 21 escolar de Barcelona. Anàlisi d’un instrument d’autoavaluació i respostes davant la proposta de la seva implementació

L’Agenda 21 Escolar de Barcelona és un programa adreçat als centres de totes les etapes educatives. Un programa d'educació, participació i implicació cívica, que actua com a estímul i suport a la introducció de criteris de sostenibilitat. Això significa que de manera progressiva, el centre es va implicant en la revisió i transformació de les pràctiques escolars, assegurant la participació real dels protagonistes, creant espais i condicions per actuar amb autonomia, responsabilitat, cooperació . . . Al finalitzar el cinquè curs d’A21E, els centres poden iniciar una nova etapa fent una memòria del quinquenni. El treball descriu una eina d’autoavaluació elaborada en el marc d’un grup de treball constituït per la coordinació del programa i professorat de centres diversos i l’anàlisi de les respostes dels claustres a l’hora de rebre la proposta i d’utilitzar l’instrument