674 research outputs found
ARPES on HTSC: simplicity vs. complexity
A notable role in understanding of microscopic electronic properties of high
temperature superconductors (HTSC) belongs to angle resolved photoemission
spectroscopy (ARPES). This technique supplies a direct window into reciprocal
space of solids: the momentum-energy space where quasiparticles (the electrons
dressed in clouds of interactions) dwell. Any interaction in the electronic
system, e.g. superconducting pairing, leads to modification of the
quasi-particle spectrum--to redistribution of the spectral weight over the
momentum-energy space probed by ARPES. A continued development of the technique
had an effect that the picture seen through the ARPES window became clearer and
sharper until the complexity of the electronic band structure of the cuprates
had been resolved. Now, in an optimal for superconductivity doping range, the
cuprates much resemble a normal metal with well predicted electronic structure,
though with rather strong electron-electron interaction. This principal
disentanglement of the complex physics from complex structure reduced the
mystery of HTSC to a tangible problem of interaction responsible for
quasi-particle formation. Here we present a short overview of resent ARPES
results, which, we believe, denote a way to resolve the HTSC puzzle.Comment: A review written for a special issue of FN
Measuring the gap in ARPES experiments
Angle-resolved photoemission spectroscopy (ARPES) is considered as the only
experimental tool from which the momentum distribution of both the
superconducting and pseudo-gap can be quantitatively derived. The binding
energy of the leading edge of the photoemission spectrum, usually called the
leading edge gap (LEG), is the model-independent quantity which can be measured
in the modern ARPES experiments with the very high accuracy--better than 1 meV.
This, however, may be useless as long as the relation between the LEG and the
real gap is unknown. We present a systematic study of the LEG as a function of
a number of physical and experimental parameters. The absolute gap values which
have been derived from the numerical simulation prove, for example that the
nodal direction in the underdoped Bi-2212 in superconducting state is really
the node--the gap is zero. The other consequences of the simulations are
discussed.Comment: revtex4, 9 pages, 6 figure
Doping dependence of the mass enhancement in (Pb,Bi)_2 Sr_2 Ca Cu_2 O_8 at the antinodal point in the superconducting and normal state
Angle-resolved photoemission spectroscopy (ARPES) is used to study the mass
renormalization of the charge carriers in the high-T_c superconductor
(Pb,Bi)_2Sr_2CaCu_2O_8 in the vicinity of the (pi,0) point in the
superconducting and the normal state. Using matrix element effects at different
photon energies and due to a high momentum and energy resolution the bonding
and the antibonding bands could be separated in the whole dopant range. A huge
anisotropic coupling to a bosonic collective mode is observed below T_c for
both bands in particular for the underdoped case. Above T_c, the more isotropic
coupling to a continuum or a mode at much higher energy is significantly
weaker.Comment: 4 revtex pages, 4 eps figure
PSY48 EPIDEMIOLOGY OF HEREDITARY COAGULOPATHIES IN RUSSIA: PATIENT-REPORTED DATA. INTERMEDIATE RESULTS. PART 2
Surprises in the doping dependence of the Fermi surface in Bi(Pb)-2212
A detailed and systematic ARPES investigation of the doping-dependence of the
normal state Fermi surface (FS) of modulation-free (Pb,Bi)-2212 is presented.
The FS does not change in topology away from hole-like at any stage. The data
reveal, in addition, a number of surprises. Firstly the FS area does not follow
the usual curve describing Tc vs x for the hole doped cuprates, but is
down-shifted in doping by ca. 0.05 holes per Cu site, indicating either the
break-down of Luttinger's theorem or the consequences of a significant bi-layer
splitting of the FS. Secondly, the strong k-dependence of the FS width is shown
to be doping independent. Finally, the relative strength of the shadow FS has a
doping dependence mirroring that of Tc.Comment: 5 pages, 4 figures (revtex
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