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An Introduction to Superconductivity
Published in David A. Cardwell, David C. Larbalestier, I. Braginski Aleksander, Handbook of Superconductivity, 2023
William F. “Joe” Vinen, Terry P. Orlando
In the case of superconducting metals, the phase transition involves the electron fluid that is responsible for electrical conductivity in the normal (high-temperature) phase. The frictionless flow is seen as a loss of electrical resistivity, the material often showing a resistivity that is unmeasurably small. Electrical resistivity is due to the scattering of the conduction electrons by imperfections in the crystal lattice in which they are moving, so one might be tempted to think that in a superconductor these scattering processes are mysteriously turned off. As explained in Pippard's historical introduction, this view is quite misleading. All superconductors exhibit the Meissner effect: in sufficiently small applied magnetic fields, they behave as perfectly diamagnetic materials, in the sense that the magnetic flux is excluded in a reversible manner; they behave just like conventional diamagnetic materials, except that they have a much larger diamagnetic susceptibility. The required screening current is maintained as part of the equilibrium state of the system just as it is in the diamagnetic screening current in a diamagnetic atom or molecule. Scattering processes, far from having disappeared, are helping to maintain this equilibrium, as we shall see a little later.
Thermodynamics
Published in Harshad K. D. H. Bhadeshia, Theory of Transformations in Steels, 2021
Diamagnetism is a weak, temperature independent negative susceptibility which causes the material to be repelled by a magnetic field. Any substance whatsoever can be diamagnetic. As discovered by Landau, an electron gas such as that associated with metallic bonding will exhibit diamagnetism because in a magnetic field, the electrons move within the metal in spirals, but in a quantised manner, about the field direction. This induced current results in a magnetic moment which, according to Lenz's law, opposes the applied field. Lenz's law states that when the flux through an electrical circuit is changed, an induced current is set up in a direction that opposes the change in flux. The real scenario may be more complex in a metal because the electron gas moves under the influence of the periodic potential associated with the ion cores within the crystal structure.
Superconductivity
Published in Elaine A. Moore, Lesley E. Smart, Solid State Chemistry, 2020
Elaine A. Moore, Lesley E. Smart
An unusual superconductor that is structurally related to the cuprates was identified in 1994: Sr2RuO4 has a crystal structure almost identical to La2CuO4, the parent compound of the high-TC superconductor 1-2-3 (see Figure 10.5). However, whereas La2CuO4 is an antiferromagnetic insulator, Sr2RuO4 is metallic and, below about 1.5 K, it is superconducting. Interest in this compound, despite its low TC, is due to the presence of ferromagnetism as well as superconductivity. Conventional superconductors are diamagnetic and, previously, diamagnetism had been thought of as a necessary condition for superconductivity. The ruthenium in Sr2RuO4 is formally present as Ru(IV), giving an electronic configuration of 4d4. The Ru is in the centre of an octahedron of oxygen and so the d bands are split into t2g and eg. The four 4d electrons partly occupy the t2g band. It is the electrons close to the highest-occupied levels of this band that are responsible for the superconductivity.
Tridimensional electric field effect on diamagnetic susceptibility and polarisability of a donor impurity in a double quantum dot
Published in Philosophical Magazine, 2023
Reda Arraoui, Ed-Dahmouny Ayoub, Ahmed Sali, Kamal El-Bakkari, Mohammed Jaouane, Abdelghani Fakkahi
By definition, the susceptibility of a sample is an extensive quantity that characterises its reaction to an applied field. The degree of polarisation of a material in regards toward to an applied electric field is measured as electric susceptibility. When we have a response to a magnetic field in the opposite sense of the applied field, we call it diamagnetic. In this respect, the diamagnetic susceptibility is used to investigate the magnetic behaviour of nanostructures. More recently, E. Iqraoun et al. [23] have studied the influence of an electric field applied on the binding energy, the diamagnetic susceptibility and polarisability of a shallow donor in a quantum dot with conical form. One of their results indicated that the field F enhances slightly the , whereas it diminishes when the electronic quantum confinement is strong. To the best of our knowledge, no theoretical research has been conducted on the influence of a tridimensional field F on the diamagnetic susceptibility and the polarisability of a shallow donor impurity in a symmetrical double QD.