Correcting 100 years of misunderstanding: electric fields in superconductors, hole superconductivity, and the Meissner effect

From the outset of superconductivity research it was assumed that no electrostatic fields could exist inside superconductors, and this assumption was incorporated into conventional London electrodynamics. Yet the London brothers themselves initially (in 1935) had proposed an electrodynamic theory of superconductors that allowed for static electric fields in their interior, which they unfortunately discarded a year later. I argue that the Meissner effect in superconductors necessitates the existence of an electrostatic field in their interior, originating in the expulsion of negative charge from the interior to the surface when a metal becomes superconducting. The theory of hole superconductivity predicts this physics, and associated with it a macroscopic spin current in the ground state of superconductors ("Spin Meissner effect"), qualitatively different from what is predicted by conventional BCS-London theory. A new London-like electrodynamic description of superconductors is proposed to describe this physics. Within this theory superconductivity is driven by lowering of quantum kinetic energy, the fact that the Coulomb repulsion strongly depends on the character of the charge carriers, namely whether electron- or hole-like, and the spin-orbit interaction. The electron-phonon interaction does not play a significant role, yet the existence of an isotope effect in many superconductors is easily understood. In the strong coupling regime the theory appears to favor local charge inhomogeneity. The theory is proposed to apply to all superconducting materials, from the elements to the high $T_c$ cuprates and pnictides, is highly falsifiable, and explains a wide variety of experimental observations.Comment: Proceedings of the conference "Quantum phenomena in complex matter 2011 - Stripes 2011", Rome, 10 July -16 July 2011, to be published in J. Supercond. Nov. Mag

A general parametrization for the long-range part of neutrinoless double beta decay

Double beta decay has been proven to be a powerful tool to constrain $B-L$ violating physics beyond the standard model. We present a representation for the long-range part of the general $0\nu\beta\beta$ decay rate allowed by Lorentz-invariance. Combined with the short range part this general parametrization in terms of effective $B-L$ violating couplings will provide the $0\nu\beta\beta$ limits on arbitrary lepton number violating theories.Comment: Talk presented by H. P\"as at the Erice School on Nuclear Physics, 19th course "Neutrinos in Astro, Particle and Nuclear Physics", Erice, Italy, 16-24 September 1997, 2 pages, Latex, requires worldsci.st

A superformula for neutrinoless double beta decay II: The short range part

A general Lorentz-invariant parameterization for the short-range part of the 0vBB decay rate is derived. Combined with the long range part already published this general parameterization in terms of effective B-L violating couplings allows one to extract the 0vBB limits on arbitrary lepton number violating theories.Comment: 8 pages, LaTeX, 2 figure

Quantum Monte Carlo and exact diagonalization study of a dynamic Hubbard model

A one-dimensional model of electrons locally coupled to spin-1/2 degrees of freedom is studied by numerical techniques. The model is one in the class of $dynamic$ $Hubbard$ $models$ that describe the relaxation of an atomic orbital upon double electron occupancy due to electron-electron interactions. We study the parameter regime where pairing occurs in this model by exact diagonalization of small clusters. World line quantum Monte Carlo simulations support the results of exact diagonalization for larger systems and show that kinetic energy is lowered when pairing occurs. The qualitative physics of this model and others in its class, obtained through approximate analytic calculations, is that superconductivity occurs through hole undressing even in parameter regimes where the effective on-site interaction is strongly repulsive. Our numerical results confirm the expected qualitative behavior, and show that pairing will occur in a substantially larger parameter regime than predicted by the approximate low energy effective Hamiltonian.Comment: Some changes made in response to referees comments. To be published in Phys.Rev.

Quasiparticle undressing in a dynamic Hubbard model: exact diagonalization study

Dynamic Hubbard models have been proposed as extensions of the conventional Hubbard model to describe the orbital relaxation that occurs upon double occupancy of an atomic orbital. These models give rise to pairing of holes and superconductivity in certain parameter ranges. Here we explore the changes in carrier effective mass and quasiparticle weight and in one- and two-particle spectral functions that occur in a dynamic Hubbard model upon pairing, by exact diagonalization of small systems. It is found that pairing is associated with lowering of effective mass and increase of quasiparticle weight, manifested in transfer of spectral weight from high to low frequencies in one- and two-particle spectral functions. This 'undressing' phenomenology resembles observations in transport, photoemission and optical experiments in high T_c cuprates. This behavior is contrasted with that of a conventional electron-hole symmetric Holstein-like model with attractive on-site interaction, where pairing is associated with 'dressing' instead of 'undressing'

R-parity violation: Hide & Seek

We point out that, if R-parity is broken spontaneously, the neutralino can decay to the final state majoron plus neutrino, which from the experimental point of view is indistinguishable from the standard missing momentum signal of supersymmetry. We identify the regions of parameter space where this decay mode is dominant and show that they are independent of R-parity conserving SUSY parameters. Thus, (a) only very weak limits on R-parity violating couplings can be derived from the observation of missing momentum events and (b) at future collider experiments huge statistics might be necessary to establish that R-parity indeed is broken. Parameter combinations which give calculated relic neutralino density larger than the measured dark matter density in case of conserved R-parity are valid points in this scenario and their phenomenology at the LHC deserves to be studied.Comment: 8 pages, 2 figures; ref. added; matches published version (title changed in the published version

Meissner effect, Spin Meissner effect and charge expulsion in superconductors

The Meissner effect and the Spin Meissner effect are the spontaneous generation of charge and spin current respectively near the surface of a metal making a transition to the superconducting state. The Meissner effect is well known but, I argue, not explained by the conventional theory, the Spin Meissner effect has yet to be detected. I propose that both effects take place in all superconductors, the first one in the presence of an applied magnetostatic field, the second one even in the absence of applied external fields. Both effects can be understood under the assumption that electrons expand their orbits and thereby lower their quantum kinetic energy in the transition to superconductivity. Associated with this process, the metal expels negative charge from the interior to the surface and an electric field is generated in the interior. The resulting charge current can be understood as arising from the magnetic Lorentz force on radially outgoing electrons, and the resulting spin current can be understood as arising from a spin Hall effect originating in the Rashba-like coupling of the electron magnetic moment to the internal electric field. The associated electrodynamics is qualitatively different from London electrodynamics, yet can be described by a small modification of the conventional London equations. The stability of the superconducting state and its macroscopic phase coherence hinge on the fact that the orbital angular momentum of the carriers of the spin current is found to be exactly $\hbar/2$, indicating a topological origin. The simplicity and universality of our theory argue for its validity, and the occurrence of superconductivity in many classes of materials can be understood within our theory.Comment: Submitted to SLAFES XX Proceeding

Electromotive forces and the Meissner effect puzzle

In a voltaic cell, positive (negative) ions flow from the low (high) potential electrode to the high (low) potential electrode, driven by an `electromotive force' which points in opposite direction and overcomes the electric force. Similarly in a superconductor charge flows in direction opposite to that dictated by the Faraday electric field as the magnetic field is expelled in the Meissner effect. The puzzle is the same in both cases: what drives electric charges against electromagnetic forces? I propose that the answer is also the same in both cases: kinetic energy lowering, or `quantum pressure'