205 research outputs found
Thermal and Quantum Fluctuations Induced Additional Gap in Single-particle Spectrum of d-p model
The possibility of thermal and quantum fluctuations induced attractive
interaction leading to a pairing gap \Delta_tq in the single-particle spectrum
of d-p model in the limit of a large N of fermion flavor is investigated
analytically. This is an anomalous pairing gap in addition to the one with
d-wave symmetry originating from partially screened, inter-site coulomb
interaction. The motivation was to search for a hierarchy of multiple many-body
interaction scales in high-Tc superconductor as suggested by recent
experimental findings. The pairing gap anisotropy stems from more than one
sources, namely, nearest neighbour hoppings and the p-d hybridization but not
the coupling of the effective interaction. The temperature at which \Delta_tq
vanishes may be driven to zero by using a tuning parameter to have access to
quantum criticality only when N >> 1. For the physical case N = 2, the usual
coherent quasi-particle feature surfaces in the spectral weight everywhere in
the momentum space below the pairing gap \Delta_tq. Thus it appears that the
reduction in spin degeneracy has the effect of masking quantum criticality.Comment: 11 pages,No figure,Accepted for publication in Physica
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The hierarchy of multiple many-body interaction scales in high-temperature superconductors
To date, angle-resolved photoemission spectroscopy has been successful in identifying energy scales of the many-body interactions in correlated materials, focused on binding energies of up to a few hundred meV below the Fermi energy. Here, at higher energy scale, we present improved experimental data from four families of high-T{sub c} superconductors over a wide doping range that reveal a hierarchy of many-body interaction scales focused on: the low energy anomaly ('kink') of 0.03-0.09eV, a high energy anomaly of 0.3-0.5eV, and an anomalous enhancement of the width of the LDA-based CuO{sub 2} band extending to energies of {approx} 2 eV. Besides their universal behavior over the families, we find that all of these three dispersion anomalies also show clear doping dependence over the doping range presented
Optical determination of the relation between the electron-boson coupling function and the critical temperature in high T cuprates
We take advantage of the connection between the free carrier optical
conductivity and the glue function in the normal state, to reconstruct from the
infrared optical conductivity the glue-spectrum of ten different high-Tc
cuprates revealing a robust peak in the 50-60 meV range and a broad con- tinuum
at higher energies for all measured charge carrier concentrations and
temperatures up to 290 K. We observe that the strong coupling formalism
accounts fully for the known strong temperature dependence of the optical
spectra of the high Tc cuprates, except for strongly underdoped samples. We
observe a correlation between the doping trend of the experimental glue spectra
and the critical temperature. The data obtained on the overdoped side of the
phase diagram conclusively excludes the electron-phonon coupling as the main
source of superconducting pairing.Comment: Accepted for publication in Phys. Rev.
Analysis of the spectral function of Nd1.85Ce0.15CuO4, obtained by angle resolved photoemission spectroscopy
Samples of Nd(2-x)Ce(x)CuO(4), an electron-doped high temperature
superconducting cuprate (HTSC), near optimal doping at x = 0.155 were measured
via angle resolved photoemission (ARPES). We report a renormalization feature
in the self energy ("kink") in the band dispersion at 50 - 60 meV present in
nodal and antinodal cuts across the Fermi surface. Specifically, while the kink
had previously only been seen in the antinodal region, it is now observed also
in the nodal region, reminiscent of what has been observed in hole-doped
cuprates.Comment: 4 pages, 4 figure
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Extracting the spectral function of the cuprates by a full two-dimensional analysis: Angle-resolved photoemission spectra of Bi2Sr2CuO6
Recently, angle-resolved photoemission spectroscopy (ARPES) has revealed a dispersion anomaly at high binding energy near 0.3-0.5 eV in various families of the high-temperature superconductors. For further studies of this anomaly we present a new two-dimensional fitting-scheme and apply it to high-statistics ARPES data of the strongly-overdoped Bi{sub 2}Sr{sub 2}CuO{sub 6} cuprate superconductor. The procedure allows us to extract the self-energy in an extended energy and momentum range. It is found that the spectral function of Bi{sub 2}Sr{sub 2}CuO{sub 6} can be parameterized using a small set of tight-binding parameters and a weakly-momentum-dependent self-energy up to 0.7 eV in binding energy and over the entire first Brillouin zone. Moreover the analysis gives an estimate of the momentum dependence of the matrix element, a quantity, which is often neglected in ARPES analyses
Calculation of overdamped c-axis charge dynamics and the coupling to polar phonons in cuprate superconductors
In our recent paper we presented empirical evidences suggesting that
electrons in cuprate superconductors are strongly coupled to unscreened c-axis
polar phonons. In the overdoped regime the c-axis metallizes and we present
here simple theoretical arguments demonstrating that the observed effect of the
metallic c-axis screening on the polar electron-phonon coupling is consistent
with a strongly overdamped c-axis charge dynamics in the optimally doped
system, becoming less dissipative in the overdoped regime.Comment: 6 pages, 1 figure. to be published in Phys. Rev.
Creation and control of a two-dimensional electron liquid at the bare SrTiO3 surface
Many-body interactions in transition-metal oxides give rise to a wide range
of functional properties, such as high-temperature superconductivity, colossal
magnetoresistance, or multiferroicity. The seminal recent discovery of a
two-dimensional electron gas (2DEG) at the interface of the insulating oxides
LaAlO3 and SrTiO3 represents an important milestone towards exploiting such
properties in all-oxide devices. This conducting interface shows a number of
appealing properties, including a high electron mobility, superconductivity,
and large magnetoresistance and can be patterned on the few-nanometer length
scale. However, the microscopic origin of the interface 2DEG is poorly
understood. Here, we show that a similar 2DEG, with an electron density as
large as 8x10^13 cm^-2, can be formed at the bare SrTiO3 surface. Furthermore,
we find that the 2DEG density can be controlled through exposure of the surface
to intense ultraviolet (UV) light. Subsequent angle-resolved photoemission
spectroscopy (ARPES) measurements reveal an unusual coexistence of a light
quasiparticle mass and signatures of strong many-body interactions.Comment: 14 pages, 4 figures, supplementary information (see other files
Strong energy-momentum dispersion of phonon-dressed carriers in the lightly doped band insulator SrTiO
Much progress has been made recently in the study of the effects of
electron-phonon (el-ph) coupling in doped insulators using angle resolved
photoemission (ARPES), yielding evidence for the dominant role of el-ph
interactions in underdoped cuprates. As these studies have been limited to
doped Mott insulators, the important question arises how this compares with
doped band insulators where similar el-ph couplings should be at work. The
archetypical case is the perovskite SrTiO (STO), well known for its giant
dielectric constant of 10000 at low temperature, exceeding that of
LaCuO by a factor of 500. Based on this fact, it has been suggested
that doped STO should be the archetypical bipolaron superconductor. Here we
report an ARPES study from high-quality surfaces of lightly doped SrTiO.
Comparing to lightly doped Mott insulators, we find the signatures of only
moderate electron-phonon coupling: a dispersion anomaly associated with the low
frequency optical phonon with a and an overall bandwidth
renormalization suggesting an overall coming from the higher
frequency phonons. Further, we find no clear signatures of the large pseudogap
or small polaron phenomena. These findings demonstrate that a large dielectric
constant itself is not a good indicator of el-ph coupling and highlight the
unusually strong effects of the el-ph coupling in doped Mott insulators
Contribution of interband effects caused by long-wavelength transverse optical phonons to electron-phonon coupling in doped polar insulators
We estimate the contribution of the long-wavelength el-TO-ph interaction and
discuss the effect it has on electron pairing in doped polar systems like
SrTiO3 and PbTe. The analytical and numerical results presented in the study
indicate that the el-TO-ph interaction tends to contribute little to the total
strength of electron-phonon coupling in these and related materials. To explain
this fact we consider possible reasons why the effect of the polar
long-wavelength transverse optical phonons on the coupling constant "lambda" is
far less than one might suppose.Comment: 5 pages, 3 table
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