84,634 research outputs found
Superconductivity from Hole Undressing
Photoemission and optical experiments indicate that the transition to
superconductivity in cuprates is an 'undressing' transition . In photoemission
this is seen as a coherent quasiparticle peak emerging from an incoherent
background, in optics as violation of the Ferrell-Glover-Tinkham sum rule
indicating effective mass reduction of superconducting carriers. We propose
that this is a manifestation of the fundamental electron-hole asymmetry of
condensed matter described by the theory of hole superconductivity. The theory
asserts that electrons in nearly empty bands and holes in nearly full bands are
fundamentally different : the former yield high conductivity and normal metals,
the latter yield low normal state conductivity and high temperature
superconductivity. This is because the normal state transport of electrons is
coherent and that of holes is incoherent. We explain how this asymmetry arises
from the Coulomb interaction between electrons in atoms and the nature of
atomic orbitals, and propose a simple Hamiltonian to describe it. A
mechanism for superconductivity follows from this physics, whereby dressed hole
carriers undress by pairing, turning (partially) into electrons and becoming
more mobile in the superconducting state.Comment: Presented at the Third International Conference on New Theories,
Discoveries, and Applications of Superconductors and Related Materials
(New3SC-3), Hawaii, January 2001, to be published in Physica
Consequences of charge imbalance in superconductors within the theory of hole superconductivity
The theory of hole superconductivity proposes that the fundamental asymmetry
between electrons and holes in solids is responsible for superconductivity.
Here we point out a remarkable consequence of this theory: a tendency for
negative charge to be expelled from the bulk of the superconductor towards the
surface. Experimentally observable consequences of this physics are discussed
Hole Superconductivity in : a high cuprate without Cu
The theory of hole superconductivity explains high temperature
superconductivity in cuprates as driven by pairing of hole carriers in oxygen
orbitals in the highly negatively charged planes. The pairing
mechanism is hole undressing and is Coulomb-interaction driven. We propose that
the planes of atoms in are akin to the planes without ,
and that the recently observed high temperature superconductivity in
arises similarly from undressing of hole carriers in the planar boron
orbitals in the negatively charged planes. Doping with electrons
and with holes should mirror the behavior of underdoped and overdoped high
cuprates respectively. We discuss possible ways to achieve higher
transition temperatures in boron compounds based on this theory.Comment: A section on isotope effect has been added, as well as other minor
change
Superconductors as giant atoms predicted by the theory of hole superconductivity
The theory of hole superconductivity proposes that superconductivity
originates in the fundamental electron-hole asymmetry of condensed matter and
that it is an 'undressing' transition. Here we propose that a natural
consequence of this theory is that superconductors behave as giant atoms. The
model predicts that the charge distribution in superconductors is
inhomogeneous, with higher concentration of negative charge near the surface.
Some of this negative charge will spill out, giving rise to a negative electron
layer right outside the surface of the superconductor, which should be
experimentally detectable. Also superconductors should have a tendency to
easily lose negative charge and become positively charged. Macroscopic spin
currents are predicted to exist in superconducting bodies, giving rise to
electric fields near the surface of multiply connected superconductors that
should be experimentally detectable.Comment: To be published in Phys.Lett.
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
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.
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
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 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
Why non-superconducting metallic elements become superconducting under high pressure
We predict that simple metals and early transition metals that become
superconducting under high pressures will show a change in sign of their Hall
coefficient from negative to positive under pressure. If verified, this will
strongly suggest that hole carriers play a fundamental role in `conventional'
superconductivity, as predicted by the theory of hole superconductivity.Comment: Submitted to M2S-IX Tokyo 200
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 ,
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
Towards an understanding of hole superconductivity
From the very beginning K. Alex M\"uller emphasized that the materials he and
George Bednorz discovered in 1986 were superconductors. Here I would
like to share with him and others what I believe to be key reason for why
high cuprates as well as all other superconductors are hole
superconductors, which I only came to understand a few months ago. This paper
is dedicated to Alex M\"uller on the occasion of his 90th birthday.Comment: Dedicated to Alex M\"uller on the Occasion of his 90th Birthday.
arXiv admin note: text overlap with arXiv:1703.0977
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