82 research outputs found
Spectroscopic distinction between the normal state pseudogap and the superconducting gap of cuprate high T_{c} superconductors
We report on broad-band infrared ellipsometry measurements of the c-axis
conductivity of underdoped RBa_{2}Cu_{3}O_{7-d} (R=Y, Nd, and La) single
crystals. Our data provide a detailed account of the spectral weight (SW)
redistributions due to the normal state pseudogap (PG) and the superconducting
(SC) gap. They show that these phenomena involve different energy scales,
exhibit distinct doping dependencies and thus are likely of different origin.
In particular, the SW redistribution in the PG state closely resembles the one
of a conventional charge- or spin density wave (CDW or SDW) system.Comment: 4 pages, 4 figure
Manifestation of pseudogap in ab-plane optical characteristics
A model in which a gap forms in the renormalized electronic density of state
(DOS) with missing states recovered just above the pseudogap , is
able to give a robust description of the striking, triangular like, peak seen
in the real part of the optical self-energy of underdoped cuprates. We use this
model to explore the effect of the pseudogap on the real part of the optical
conductivity and on the partial sum rule associated with it. An important
result is that the optical spectral weight redistributes over a much larger
frequency window than it does in the DOS.Comment: 12 pages, 3 figures. Submitted to Journal of Physics: Condensed
Matte
C-axis lattice dynamics in Bi-based cuprate superconductors
We present results of a systematic study of the c axis lattice dynamics in
single layer Bi2Sr2CuO6 (Bi2201), bilayer Bi2Sr2CaCu2O8 (Bi2212) and trilayer
Bi2Sr2Ca2Cu3O10 (Bi2223) cuprate superconductors. Our study is based on both
experimental data obtained by spectral ellipsometry on single crystals and
theoretical calculations. The calculations are carried out within the framework
of a classical shell model, which includes long-range Coulomb interactions and
short-range interactions of the Buckingham form in a system of polarizable
ions. Using the same set of the shell model parameters for Bi2201, Bi2212 and
Bi2223, we calculate the frequencies of the Brillouin-zone center phonon modes
of A2u symmetry and suggest the phonon mode eigenvector patterns. We achieve
good agreement between the calculated A2u eigenfrequencies and the experimental
values of the c axis TO phonon frequencies which allows us to make a reliable
phonon mode assignment for all three Bi-based cuprate superconductors. We also
present the results of our shell model calculations for the Gamma-point A1g
symmetry modes in Bi2201, Bi2212 and Bi2223 and suggest an assignment that is
based on the published experimental Raman spectra. The
superconductivity-induced phonon anomalies recently observed in the c axis
infrared and resonant Raman scattering spectra in trilayer Bi2223 are
consistently explained with the suggested assignment.Comment: 29 pages, 13 figure
Extracting the electron--boson spectral function F() from infrared and photoemission data using inverse theory
We present a new method of extracting electron-boson spectral function
F() from infrared and photoemission data. This procedure is
based on inverse theory and will be shown to be superior to previous
techniques. Numerical implementation of the algorithm is presented in detail
and then used to accurately determine the doping and temperature dependence of
the spectral function in several families of high-T superconductors.
Principal limitations of extracting F() from experimental
data will be pointed out. We directly compare the IR and ARPES
F() and discuss the resonance structure in the spectra in
terms of existing theoretical models
Transverse optical Josephson plasmons, equations of motion
A detailed calculation is presented of the dielectric function in
superconducttors consisting of two Josephson coupled superconducting layers per
unit cell, taking into account the effect of finite compressibility of the
electron fluid. From the model it follows, that two longitudinal, and one
transverse optical Josephson plasma resonance exist in these materials, for
electric field polarization perpendicular to the planes. The latter mode
appears as a resonance in the transverse dielectric function, and it couples
directly to the electrical field vector of infrared radiation. A shift of all
plasma frequencies, and a reduction of the intensity of the transverse optical
Josephson plasmon is shown to result from the finite compressibility of the
electron fluid.Comment: 17 pages, ReVTeX, 7 figures in eps forma
Evidence of precursor superconductivity as high as 180 K from infrared spectroscopy
We show that a multilayer analysis of the infrared c-axis response of
RBa2Cu3O7-d (R=Y, Gd, Eu) provides important new information about the
anomalous normal state properties of underdoped cuprate high temperature
superconductors. Besides competing correlations which give rise to a pseudogap
that depletes the low-energy electronic states below T*>>Tc, it enables us to
identify the onset of a precursor superconducting state below Tons>Tc. We map
out the doping phase diagram of Tons which reaches a maximum of ~180 K at
strong underdoping and present magnetic field dependent data which confirm our
conclusions.Comment: 5 pages, 3 figure
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