138 research outputs found
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
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.
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
Angle-resolved photoemission spectroscopy study of HgBaCuO
HgBaCuO (Hg1201) has been shown to be a model cuprate for
scattering, optical, and transport experiments, but angle-resolved
photoemission spectroscopy (ARPES) data are still lacking owing to the absence
of a charge-neutral cleavage plane. We report on progress in achieving the
experimental conditions for which quasiparticles can be observed in the
near-nodal region of the Fermi surface. The d-wave superconducting gap is
measured and found to have a maximum of 39 meV. At low temperature, a kink is
detected in the nodal dispersion at approximately 51 meV below the Fermi level,
an energy that is different from other cuprates with comparable T. The
superconducting gap, Fermi surface, and nodal band renormalization measured
here provide a crucial momentum-space complement to other experimental probes
Quasiparticle dynamics and spin-orbital texture of the SrTiO3 two-dimensional electron gas
Two-dimensional electron gases (2DEGs) in SrTiO have become model systems
for engineering emergent behaviour in complex transition metal oxides.
Understanding the collective interactions that enable this, however, has thus
far proved elusive. Here we demonstrate that angle-resolved photoemission can
directly image the quasiparticle dynamics of the -electron subband ladder of
this complex-oxide 2DEG. Combined with realistic tight-binding supercell
calculations, we uncover how quantum confinement and inversion symmetry
breaking collectively tune the delicate interplay of charge, spin, orbital, and
lattice degrees of freedom in this system. We reveal how they lead to
pronounced orbital ordering, mediate an orbitally-enhanced Rashba splitting
with complex subband-dependent spin-orbital textures and markedly change the
character of electron-phonon coupling, co-operatively shaping the low-energy
electronic structure of the 2DEG. Our results allow for a unified understanding
of spectroscopic and transport measurements across different classes of
SrTiO-based 2DEGs, and yield new microscopic insights on their functional
properties.Comment: 10 pages including supplementary information, 4+4 figure
- …