Search

We propose an effective theory of non-Abelian superconductivity, an SU(2)xU(1) extension of the Abelian Landau-Ginzburg theory, which could be viewed as an effective theory of ferromagnetic superconductivity made of spin-up and spin-down doublet Cooper pair. Just like the Abelian Landau-Ginzburg theory it has the U(1) electromagnetic interaction, but the new ingredient is the non-Abelian SU(2) gauge interaction between the spin doublet Cooper pairs. A remarkable feature of the theory is the mixing between the U(1) gauge boson and the diagonal part of the SU(2) gauge boson. After the mixing it has a massless non-Abelian gauge boson (the massless s-boson) and massive gauge boson (the massive photon), in addition to the massive off-diagonal non-Abelian gauge bosons (the massive s-bosons) which induce the spin-flip interaction between the spin up and down components of the Cooper pair. So, unlike the ordinary Landau-Ginzburg theory it has a long range interaction mediated by the massless s-boson, which could be responsible for the long range magnetic order and spin waves observed in ferromagnetic superconductors. The theory is characterized by three scales. In addition to the correlation length fixed by the mass of the Higgs field it has two different penetration lengths, the one fixed by the mass of the photon (which generates the well known Meissner effect) and the other fixed by the mass of the off-diagonal gauge bosons (which determines the range of the spin flip interaction). The non-Abelian structure of the theory naturally accommodates new topological objects, the non-Abrikosov quantized spin vortex (as well as the well known Abrikosov vortex) and non-Abelian spin monopole. We discuss the physical implications of the non-Abelian Landau-Ginzburg theory. • The SU(2)xU(1) extension of the Abelian Landau-Ginzburg theory, is proposed. • The massless non-Abelian gauge boson induces the long range magnetic order in the ferromagnetic superconductors. [ABSTRACT FROM AUTHOR]

It is generally believed that the laws of thermodynamics govern superconductivity as an equilibrium state of matter, and hence that the normal-superconductor transition in a magnetic field is reversible under ideal conditions. Because eddy currents are generated during the transition as the magnetic flux changes, the transition has to proceed infinitely slowly to generate no entropy. Experiments showed that to a high degree of accuracy no entropy was generated in these transitions. However, in this paper we point out that for the length of times over which these experiments extended, a much higher degree of irreversibility due to decay of eddy currents should have been detected than was actually observed. We also point out that within the conventional theory of superconductivity no explanation exists for why no Joule heat is generated in the superconductor to normal transition when the supercurrent stops. In addition we point out that within the conventional theory of superconductivity no mechanism exists for the transfer of momentum between the supercurrent and the body as a whole, which is necessary to ensure that the transition in the presence of a magnetic field respects momentum conservation. We propose a solution to all these questions based on the alternative theory of hole superconductivity. The theory proposes that in the normal-superconductor transition there is a flow and backflow of charge in direction perpendicular to the phase boundary when the phase boundary moves. We show that this flow and backflow explains the absence of Joule heat generated by Faraday eddy currents, the absence of Joule heat generated in the process of the supercurrent stopping, and the reversible transfer of momentum between the supercurrent and the body, provided the current carriers in the normal state are holes . [ABSTRACT FROM AUTHOR]

The analysis of Pippard (1950) for the growth of the normal phase into the superconducting phase in the presence of a magnetic field H > H c is applied in reverse to the case H < H c ( H c = critical magnetic field). We carry out the analysis both for a planar and a cylindrical geometry. As the superconducting phase grows into the normal phase, a supercurrent is generated at the superconductor–normal phase boundary that flows in direction opposite to the Faraday electric field resulting from the moving phase boundary. This supercurrent motion is in direction opposite to what is dictated by the Lorentz force on the current carriers, and in addition requires that mechanical momentum of opposite sign be transferred to the system as a whole to ensure momentum conservation. In the cylindrical geometry case, a macroscopic torque of unknown origin acts on the body as a whole as the magnetic field is expelled. We argue that the conventional BCS-London theory of superconductivity cannot explain these facts, and that as a consequence the Meissner effect remains unexplained within the conventional theory of superconductivity. We propose that the Meissner effect can only be understood by assuming that there is motion of charge in direction perpendicular to the normal–superconductor phase boundary and point out that the unconventional theory of hole superconductivity describes this physics. [ABSTRACT FROM AUTHOR]

Abstract: Superconductivity in carbon nanotubes (CNTs) is attracting considerable attention. Recently, we have reported successful boron doping into single-walled CNTs (SWNTs) and also revealed its correlation with superconductivity. In the present study, we report results of high-pressure magnetization measurements in films consisting of ropes of boron-doped SWNTs. It reveals that and magnitude for Meissner effect are mostly independent of applied pressure, while the magnitude of graphite diamagnetism drastically increases as pressure increases. We also report the observation of resistance drop and correlation of boron doping with multi-walled CNTs, in which we reported superconductivity previously. [Copyright &y& Elsevier]

Abstract: We apply the Bogoliubov-de Gennes equations to the confinement of a monopole–antimonopole pair in a superconductor. This is related to the problem of a quark–antiquark pair bound by a confining string, consisting of a colour-electric flux tube, dual to the magnetic vortex of type-II superconductors. We study the confinement of the field lines due to the superconducting state and calculate the effective potential between the two monopoles. The monopoles can be simulated in a real experiment inserting two long and thin magnetic rods. At short distances the potential is Coulombic and at large distances the potential is linear, as previously determined solving the Ginzburg–Landau equations. The magnetic field lines and the string tension are also studied as a function of the temperature T. Because we take into account the explicit fermionic degrees of freedom, this work may open new perspectives to the breaking of chiral symmetry or to colour superconductivity. [Copyright &y& Elsevier]

The recently discovered APt 3 P (A = Sr, Ca, La) family of superconductors offers a platform to study frequency dependent superconducting phenomena as the electron–phonon coupling varies from weak to strong. Here we perform ab initio Eliashberg theory calculations to investigate two such phenomena, the occurrence of dip-hump structures in the tunneling spectra and the magnetic field induced coexistence of even and odd frequency superconductivity in these compounds. By calculating the superfluid density, we make materials specific predictions for the occurrence of the paramagnetic Meissner effect as a hallmark of odd frequency pairing. Our results provide a link between two seemingly uncorrelated aspects of even and odd frequency superconductivity and provide theoretical guidance for the future experimental identification of bulk odd frequency superconductivity in this materials' family. • Ab initio Eliashberg calculations for even and odd frequency superconductivity. • Focus on the APt 3 P (A=Sr,Ca,La) family of superconductors. • Self-consistently calculated tunneling dip-hump and paramagnetic Meissner effect. • Predictions for experimentally identifying bulk odd frequency superconductivity. [ABSTRACT FROM AUTHOR]

In this article we employ the matching method to analytically investigate the properties of holographic superconductors in the framework of Maxwell electrodynamics taking into account the effects of back reaction on spacetime. The relationship between the critical temperature (T c) and the charge density (ρ) has been obtained first. The influence of back reaction on Meissner like effect in this holographic superconductor is then studied. The results for the critical temperature indicate that the condensation gets harder to form when we include the effect of back reaction. We also give a detailed discussion about the dependence of our results on the choice of the matching point. The expression for the critical magnetic field (B c) above which the superconducting phase vanishes is next obtained. It is observed from our investigation that the ratio of B c and T c 2 increases with the increase in the back reaction parameter. However, the critical magnetic field B c decreases with increase in the back reaction parameter. [ABSTRACT FROM AUTHOR]

The paper contains several incorrect statements related to the fact that the key issues of reversibility of the normal-superconductor transition [1] and the hole-like nature of the normal charge carriers [2] were not properly recognized. Even though these issues were clarified in subsequent publications [3,4] , we believe it should be useful for the reader that we clarify here which of the statements in this paper are incorrect. [ABSTRACT FROM AUTHOR]