335 research outputs found
About the relation between the quasiparticle Green's function in cuprates obtained from ARPES data and the magnetic susceptibility
Angle resolved photoemission spectroscopy (ARPES) provides a detailed view of
the renormalized band structure in cuprates and, consequently, is a key to the
self-energy and the quasiparticle Green's function. Such information gives a
clue to the comparison of ARPES with scanning tunneling microscopy, inelastic
neutron scattering (INS), and Raman scattering data. Here we touch on a
potential possibility of such a comparison with the dynamical magnetic
susceptibility measured in INS experiments. Calculations based on the
experimentally measured quasiparticle self-energies in cuprates lead to the
estimated magnetic susceptibility response with many-body effects taken into
account.Comment: Will be presented at the M2S-HTSC-VIII conference in Dresde
From tunneling to photoemission: correlating two spaces
Correlating the data measured by tunneling and photoemission spectroscopies
is a long-standing problem in condensed matter physics. The quasiparticle
interference, recently discovered in high-Tc cuprates, reveals a possibility to
solve this problem. Application of modern phase retrieval algorithms to Fourier
transformed tunneling data allows to recover the distribution of the
quasiparticle spectral weight in the reciprocal space of solids measured
directly by photoemission. This opens a direct way to unify these two powerful
techniques and may help to solve a number of problems related with space/time
inhomogeneities predicted in strongly correlated electron systems.Comment: more info at http://www.imp.kiev.ua/~kord/AC-ARPES/index.htm
Determination of critical current density in melt-processed HTS bulks from levitation force measurements
A simple approach to describe the levitation force measurements on
melt-processed HTS bulks was developed. A couple of methods to determine the
critical current density were introduced. The averaged -plane
values for the field parallel to this plane were determined. The first and
second levitation force hysteresis loops calculated with these values
coincide remarkably well with the experimental data.Comment: 10 pages (tex), 2 figures (in jpeg
Singular Fermi Surfaces II. The Two--Dimensional Case
We consider many--fermion systems with singular Fermi surfaces, which contain
Van Hove points where the gradient of the band function
vanishes. In a previous paper, we have treated the case of spatial dimension . In this paper, we focus on the more singular case and establish
properties of the fermionic self--energy to all orders in perturbation theory.
We show that there is an asymmetry between the spatial and frequency
derivatives of the self--energy. The derivative with respect to the Matsubara
frequency diverges at the Van Hove points, but, surprisingly, the self--energy
is in the spatial momentum to all orders in perturbation theory, provided
the Fermi surface is curved away from the Van Hove points. In a prototypical
example, the second spatial derivative behaves similarly to the first frequency
derivative. We discuss the physical significance of these findings.Comment: 68 pages LaTeX with figure
An ARPES view on the high-Tc problem: phonons vs spin-fluctuations
We review the search for a mediator of high-Tc superconductivity focusing on
ARPES experiment. In case of HTSC cuprates, we summarize and discuss a
consistent view of electronic interactions that provides natural explanation of
both the origin of the pseudogap state and the mechanism for high temperature
superconductivity. Within this scenario, the spin-fluctuations play a decisive
role in formation of the fermionic excitation spectrum in the normal state and
are sufficient to explain the high transition temperatures to the
superconducting state while the pseudogap phenomenon is a consequence of a
Peierls-type intrinsic instability of electronic system to formation of an
incommensurate density wave. On the other hand, a similar analysis being
applied to the iron pnictides reveals especially strong electron-phonon
coupling that suggests important role of phonons for high-Tc superconductivity
in pnictides.Comment: A summary of the ARPES part of the Research Unit FOR538,
http://for538.wmi.badw.d
Electronic band structure of optimal superconductors: from cuprates to ferropnictides and back again
While the beginning decade of the high-Tc cuprates era passed under
domination of local theories, Abrikosov was one of the few who took seriously
the electronic band structure of cuprates, stressing the importance of an
extended Van Hove singularity near the Fermi level. These ideas have not been
widely accepted that time mainly because of a lack of experimental evidence for
correlation between saddle point position and superconductivity. In this short
contribution, based on the detailed comparison of the electronic band
structures of different families of cuprates and iron based superconductors I
argue that a general mechanism of the Tc enhancement in all known high-Tc
superconductors is likely related with the proximity of certain Van Hove
singularities to the Fermi level. While this mechanism remains to be fully
understood, one may conclude that it is not related with the electron density
of states but likely with some kind of resonances caused by a proximity of the
Fermi surface to topological Lifshitz transition. One may also notice that the
electronic correlations often shifts the electronic bands to optimal for
superconductivity positions
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