Predicted electric field near small superconducting ellipsoids

We predict the existence of large electric fields near the surface of superconducting bodies of ellipsoidal shape of dimensions comparable to the penetration depth. The electric field is quadrupolar in nature with significant corrections from higher order multipoles. Prolate (oblate) superconducting ellipsoids are predicted to exhibit fields consistent with negative (positive) quadrupole moments, reflecting the fundamental charge asymmetry of matter.Comment: To be published in Phys.Rev.Let

Superconductivity from Undressing

Photoemission experiments in high $T_c$ cuprates indicate that quasiparticles are heavily 'dressed' in the normal state, particularly in the low doping regime. Furthermore these experiments show that a gradual undressing occurs both in the normal state as the system is doped and the carrier concentration increases, as well as at fixed carrier concentration as the temperature is lowered and the system becomes superconducting. A similar picture can be inferred from optical experiments. It is argued that these experiments can be simply understood with the single assumption that the quasiparticle dressing is a function of the local carrier concentration. Microscopic Hamiltonians describing this physics are discussed. The undressing process manifests itself in both the one-particle and two-particle Green's functions, hence leads to observable consequences in photoemission and optical experiments respectively. An essential consequence of this phenomenology is that the microscopic Hamiltonians describing it break electron-hole symmetry: these Hamiltonians predict that superconductivity will only occur for carriers with hole-like character, as proposed in the theory of hole superconductivity

Superconductivity from Undressing. II. Single Particle Green's Function and Photoemission in Cuprates

Experimental evidence indicates that the superconducting transition in high $T_c$ cuprates is an 'undressing' transition. Microscopic mechanisms giving rise to this physics were discussed in the first paper of this series. Here we discuss the calculation of the single particle Green's function and spectral function for Hamiltonians describing undressing transitions in the normal and superconducting states. A single parameter, $\Upsilon$, describes the strength of the undressing process and drives the transition to superconductivity. In the normal state, the spectral function evolves from predominantly incoherent to partly coherent as the hole concentration increases. In the superconducting state, the 'normal' Green's function acquires a contribution from the anomalous Green's function when $\Upsilon$ is non-zero; the resulting contribution to the spectral function is $positive$ for hole extraction and $negative$ for hole injection. It is proposed that these results explain the observation of sharp quasiparticle states in the superconducting state of cuprates along the $(\pi,0)$ direction and their absence along the $(\pi,\pi)$ direction.Comment: figures have been condensed in fewer pages for easier readin

Kinetic energy driven superfluidity and superconductivity and the origin of the Meissner effect

Superfluidity and superconductivity have many elements in common. However, I argue that their most important commonality has been overlooked: that both are kinetic energy driven. Clear evidence that superfluidity in $^4He$ is kinetic energy driven is the shape of the $\lambda$ transition and the negative thermal expansion coefficient below $T_\lambda$. Clear evidence that superconductivity is kinetic energy driven is the Meissner effect: I argue that otherwise the Meissner effect would not take place. Associated with this physics I predict that superconductors expel negative charge from the interior to the surface and that a spin current exists in the ground state of superconductors (spin Meissner effect). I propose that this common physics of superconductors and superfluids originates in rotational zero point motion. This view of superconductivity and superfluidity implies that rotational zero-point motion is a fundamental property of the quantum world that is missed in the current understanding.Comment: Presented at New3sc

Why holes are not like electrons: A microscopic analysis of the differences between holes and electrons in condensed matter

We give a detailed microscopic analysis of why holes are different from electrons in condensed matter. Starting from a single atom with zero, one and two electrons, we show that the spectral functions for electrons and for holes are qualitatively different because of electron-electron interactions. The quantitative importance of this difference increases as the charge of the nucleus decreases. Extrapolating our atomic analysis to the solid, we discuss the expected differences in the single particle spectral function and in frequency dependent transport properties for solids with nearly empty and nearly full electronic energy bands. We discuss the expected dependence of these quantities on doping, and the physics of superconductivity that results. We also discuss how these features of the atomic physics can be modeled by a variety of model Hamiltonians.Comment: Title was changed at editor's request. Other minor changes. To be published in Phys.Rev.

Superconductors as giant atoms: qualitative aspects

When the Fermi level is near the top of a band the carriers (holes) are maximally dressed by electron-ion and electron-electron interactions. The theory of hole superconductivity predicts that only in that case can superconductivity occur, and that it is driven by $undressing$ of the carriers at the Fermi energy upon pairing. Indeed, experiments show that dressed hole carriers in the normal state become undressed electron carriers in the superconducting state. This leads to a description of superconductors as giant atoms, where undressed time-reversed electrons are paired and propagate freely in a uniform positive background. The pairing gap provides rigidity to the wavefunction, and electrons in the giant atom respond to magnetic fields the same way as electrons in diamagnetic atoms. We predict that there is an electric field in the interior of superconductors and that the charge distribution is inhomogeneous, with higher concentration of negative charge near the surface; that the ground state of superconductors has broken parity and possesses macroscopic spin currents, and that negative charge spills out when a body becomes superconducting.Comment: Presented at the meeting 'Highlights in Condensed Matter Physics' in honor of the 60th birthday of Prof. Ferdinando Mancini, May 9-11, 2003, Salerno, Ital