97,195 research outputs found
Influence of the atomic-scale inhomogeneity of the pair interaction on extracted from the STM spectra characteristics of high- superconductors
The influence of the atomic-scale inhomogeneities of the pairing interaction
strength on the superconducting order parameter and the conductance spectra
measurable by STM is studied in the framework of weak-coupling BCS-like theory
for two-dimensional lattice model. First of all, it is found that the
inhomogeneity having the form of atomic-scale regions of enhanced pair
interaction increases the ratio of the local low-temperature gap in
differential conductance spectra to the local temperature of vanishing the gap
. Even in the framework of mean-field treatment this ratio is
shown to be larger than the one corresponding to the homogeneous case. It is
shown that the effect of thermal phase fluctuations of the superconducting
order parameter can further increase this ratio. Taking them into account in
the framework of a toy model we obtained the ratio to be . It is found that the additional atomic-scale hopping element disorder and
weak potential scatterers, which can also take place in cuprate materials, have
no considerable effect on the statistical properties of the system, including
the distribution of the gaps, and the ratio . The second
consequence of the atomic-scale order parameter inhomogeneity is the
anticorrelation between the low-temperature gap and the high-temperature
zero-bias conductance. The obtained results could bear a relation to recent STM
measurements.Comment: 14 pages, 13 figure
Electron spin relaxation in graphene: the role of the substrate
Theory of the electron spin relaxation in graphene on the SiO substrate
is developed. Charged impurities and polar optical surface phonons in the
substrate induce an effective random Bychkov-Rashba-like spin-orbit coupling
field which leads to spin relaxation by the D'yakonov-Perel' mechanism.
Analytical estimates and Monte Carlo simulations show that the corresponding
spin relaxation times are between micro- to milliseconds, being only weakly
temperature dependent. It is also argued that the presence of adatoms on
graphene can lead to spin lifetimes shorter than nanoseconds.Comment: 5 pages, 4 figure
All Abelian Quotient C.I.-Singularities Admit Projective Crepant Resolutions in All Dimensions
For Gorenstein quotient spaces , a direct generalization of the
classical McKay correspondence in dimensions would primarily demand
the existence of projective, crepant desingularizations. Since this turned out
to be not always possible, Reid asked about special classes of such quotient
spaces which would satisfy the above property. We prove that the underlying
spaces of all Gorenstein abelian quotient singularities, which are embeddable
as complete intersections of hypersurfaces in an affine space, have
torus-equivariant projective crepant resolutions in all dimensions. We use
techniques from toric and discrete geometry.Comment: revised version of MPI-preprint 97/4, 35 pages, 13 figures,
latex2e-file (preprint.tex), macro packages and eps-file
Spin-density induced by electromagnetic wave in two-dimensional electron gas
We consider the magnetic response of a two-dimensional electron gas (2DEG)
with a spin-orbit interaction to a long-wave-length electromagnetic excitation.
We observe that the transverse electric field creates spin polarization
perpendicular to the 2DEG plane. The effect is more prominent in clean systems
with resolved spin-orbit-split subbands, and reaches maximum when the frequency
of the wave matches the subband splitting at the Fermi momentum. The relation
of this effect to the spin-Hall effect is discussed.Comment: Final published for
Diverging Entanglement Length in Gapped Quantum Spin Systems
We prove the existence of gapped quantum Hamiltonians whose ground states
exhibit an infinite entanglement length, as opposed to their finite correlation
length. Using the concept of entanglement swapping, the localizable
entanglement is calculated exactly for valence bond and finitely correlated
states, and the existence of the so--called string-order parameter is
discussed. We also report on evidence that the ground state of an
antiferromagnetic chain can be used as a perfect quantum channel if local
measurements on the individual spins can be implemented.Comment: 4 page
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