Superconducting tunnel junctions (STJs) can be used as high-resolution energy-dispersive X-ray detectors. STJ detectors are based on the measurement of an increased tunneling current from excess charge carriers that are excited above the superconducting energy gap by the absorption of an X-ray. Nb-based STJ detectors have a theoretical energy resolution limit below 5 eV FWHM for X-ray energies ...

The formation of bound states at surfaces of materials with an energy gap in the bulk electron spectrum is a well known physical phenomenon. At superconductor surfaces, quasiparticles with energies inside the superconducting gap ∆ may be trapped in bound states in quantum wells, formed by total reflection against the vacuum and total Andreev reflection against the superconductor. Since an elect...

We use a total Hamiltonian containing both an electron-phonon induced attractive part of the interaction between electrons, and a Coulomb repulsive part formulated in the Hubbard modelBy diagonalising it in the Bogoliubov and Valatin mean field approximation, we obtain equations for a two valued superconducting gap function, with a much more precise statement about the repulsive cut off energy ...

We study the magnetization dynamics in a ferromagnet/insulator/superconductor tunnel junction and the associated buildup of the electrical polarization. We show that for an open circuit, the induced voltage varies strongly and nonmonotonically with the precessional frequency, and can be enhanced significantly by the superconducting correlations. For frequencies much smaller or much larger than ...

Magnetic and nonmagnetic impurities in correlated electron systems are an important probe of the properties of the host material. There is large and growing body of research on impurities in high-temperature superconductors.[1, 2] The refinement of experimental techniques probing local properties stimulated the theoretical work on defects in those systems. The investigation of the effects of Zn...

Wehave recently used inelastic neutron scattering to measure themagnetic excitation spectrum of La1.875Ba0.125CuO4 up to 200 meV. This particular cuprate is of interest because it exhibits static charge and spin stripe order. The observed spectrum is remarkably similar to that found in superconducting YBa2Cu3O6+x and La2−xSrxCuO4; the main differences are associated with the spin gap. We sugges...

Superconductivity in small metallic specimens is studied with regard to the size dependence of the parity gap (∆P ), a parameter distinguishing between the energy of even and odd number of electrons in the granule. ∆P is shown to be an increasing function of level spacing δ. The energy gap of superconductor ∆, on the other hand, decreases with increasing δ and vanishes at δ = δc which is of the...

Conventional superconductivity follows Bardeen-Cooper-Schrieffer(BCS) theory of electrons-pairing in momentum-space, while superfluidity is the Bose-Einstein condensation(BEC) of atoms paired in real-space. These properties of solid metals and ultra-cold gases, respectively, are connected by the BCS-BEC crossover. Here we investigate the band dispersions in FeTe(0.6)Se(0.4)(Tc = 14.5 K ~ 1.2 me...

I present the detailed behavior of phonon dispersion curves near momenta which span the electronic Fermi sea in a superconductor. I demonstrate that an anomaly, similar to the metallic Kohn anomaly, exists in a superconductor’s dispersion curves when the frequency of the phonon spanning the Fermi sea exceeds twice the superconducting energy gap. This anomaly occurs at approximately the same mom...

We performed a reverse process of the usual optical data analysis of boson-exchange superconductors. We calculated the optical self-energy from two (MMP and MMP+peak) input model electron-boson spectral density functions using Allen's formula for one normal and two (s- and d-wave) superconducting cases. We obtained the optical constants including the optical conductivity and the dynamic dielect...