Search results for "conductivity"
showing 10 items of 1988 documents
Vortex-creep activation energy in YBa2Cu3O7/PrBa2Cu3O7 superlattices
2010
Abstract YBa 2 Cu 3 O 7 /PrBa 2 Cu 3 O 7 (YBCO/PBCO) superlattices with a different ratio of the superconducting and insulating layer thicknesses were prepared by high pressure dc sputtering. The vortex-creep activation energy U 0 was determined by analyzing the in-plane resistive transition of 200 μm wide bridges with the external magnetic field B oriented along the c axis. It was found that U 0 is proportional to the thickness of the YBCO layers, and does only weakly depend on the PBCO layer thickness, when the latter exceeds two unit cells. We observed a change in the variation of U 0 with the current I in the specimen: U 0 exhibits a plateau in the low- I region, then decreases signific…
The quality factor of a superconducting rf resonator in a magnetic field.
2010
The quality factor of a superconducting NbTi resonator at 1.6 MHz in a magnetic field up to 1.2 T as well as its temperature dependence is investigated. A hysteresis effect in the superconducting surface resistance as a function of the magnetic field is observed. An unloaded Q-value of the resonator of 40,500 is achieved at 3.9 K. It is shown that this Q-value is limited by dielectric losses in the FORMVAR insulation of the coils wire. The details of the Q-value optimization are discussed. In the temperature dependence of the Q-value a steep decrease is observed above T approximately = 7.5 K. Finally, the implications of these measurements for real trap experiments are discussed in detail.
The explicative power of the vector potential for superconductivity: a path for high school
2014
In the classroom practice the notion of the magnetic vector potential is never introduced, both because it is not contained in secondary school textbooks and because teachers usually associate this concept with complex topics they dealt with in their university courses. In our experience instead, we have found that the introduction of the vector potential can be of great help in students’ understanding of electromagnetism and modern physics topics. In this paper we will show how the use of the vector potential allows a phenomenological and consistent explanation of superconductivity at a level suitable for high school students. We will deal with the two main aspects of superconductivity: th…
Size-dependent enhancement of superconductivity in Al and Sn nanowires: shape-resonance effect
2006
A shape-dependent superconducting resonance can be expected when an energy level associated with the transverse motion in a wire passes through the Fermi surface. We show that the recently observed width-dependent increase of ${T}_{c}$ in Al and Sn nanowires is a consequence of this shape-resonance effect.
Ag/(Bi, Pb)-Sr-Ca-Cu-O superconducting tape processing: Solid state chemistry aspects
1993
Abstract Different preparation methods have been used to obtain starting powders used in the fabrication of composite tapes by the powder-in-tube method. The effect of these distinct starting powders on the superconducting properties of Ag/Bi-Sr-Ca-Cu-O monofilament tapes has been investigated. The changes in the physical properties, including the critical current density at 77 K and ac magnetic susceptibility, and microstructure, using optical and electronic microscopy, have been analyzed in relation to the solid state reactions involved in the Bi 2 Sr 2 CaCu 2 O 8+δ and Bi 2 Sr 2 Ca 2 Cu 3 O 10+δ phase transformations.
Intercalation effect on hyperfine parameters of Fe in FeSe superconductor with Tc = 42 K
2015
57Fe-Mossbauer spectra of superconducting beta-FeSe, the Li/NH3 intercalate product and a subsequent sample of this intercalate treated with moist He gas have been measured in temperature range 4.7 - 290 K. A correlation is established between hyperfine parameters and critical temperature Tc in these phases. A strong increase of isomer shift upon intercalation is explained by a charge transfer from the Li/NH3 intercalate to the FeSe layers resulting in an increase of Tc up to 42 K. A significant decrease of the quadrupole splitting above 240 K has been attributed to diffusive motion of Li+ ions within the interlamellar space.
Anomalous magnetic hysteresis in the microwave surface resistance of MgB2 superconductor
2007
We report experimental results of the field-induced variations of the microwave surface resistance in samples of MgB2, produced by different methods. By sweeping the DC magnetic field at increasing and decreasing values, we have detected a magnetic hysteresis that can be ascribed to the different magnetic induction, due to the critical state of the fluxon lattice. The hysteresis observed in the bulk samples has an unusual shape, which cannot be justified in the framework of the critical-state models.
Field-induced suppression of the pi-band superconductivity and magnetic hysteresis in the microwave surface resistance of MgB_2 at temperatures near …
2009
We report on the magnetic-field-induced variations of the microwave surface resistance, R_s, in a polycrystalline MgB_2 sample, at different values of temperature. We have detected a magnetic hysteresis in R_s, which exhibits an unexpected plateau on decreasing the DC magnetic field below a certain value. In particular, at temperatures near T_c the hysteresis manifests itself only through the presence of the plateau. Although we do not quantitatively justify the anomalous shape of the magnetic hysteresis, we show that the results obtained in the reversible region of the R_s(H) curve can be quite well accounted for by supposing that, in this range of magnetic field, the pi-gap is almost supp…
Prediction of pressure-induced superconductivity in the novel ternary system ScCaH2n (n = 1–6)
2021
Hydrogen-rich systems are currently thought to constitute the most promising potential high-temperature superconductor materials. Here, the high-pressure structure and superconductivity of the ternary hydrogen-rich system ScCaH2n (n = 1–6) are systematically investigated by using the prediction method of particle swarm optimization structure combined with first-principles calculations. As n increases, the electron local function (ELF) indicates that the hydrogen atoms in this system exhibit different behaviors corresponding to single H atoms, H2 molecules, graphene-like layers and, ultimately, H clathrate cages. The electron phonon coupling (EPC) calculation shows that the superconducting t…
Transient DC-Arc Voltage Model in the Hybrid Switch of the DTT Fast Discharge Unit
2021
The focus of this work is the transient modelling of the DC-arc voltage on a Hybrid Switch (a mechanical switch in parallel with a static switch) of a key protection component called Fast Discharge Unit (FDU) in the Divertor Tokamak Test (DTT). The DTT facility is an experimental tokamak in advanced design and realization phase, which will be built in the ENEA Research Centre in Frascati (Italy). The FDU allows the safe discharge of the Toroidal Field (TF) superconducting magnets when a quench is detected or a failure occurs in the power supply or in the cryogenic system. In this work, the arc conductance of the mechanical By-Pass Switch (BPS) of the Hybrid Switch is modelled using the well…