9 research outputs found
The coherent {\it d}-wave superconducting gap in underdoped LaSrCuO as studied by angle-resolved photoemission
We present angle-resolved photoemission spectroscopy (ARPES) data on
moderately underdoped LaSrCuO at temperatures below and
above the superconducting transition temperature. Unlike previous studies of
this material, we observe sharp spectral peaks along the entire underlying
Fermi surface in the superconducting state. These peaks trace out an energy gap
that follows a simple {\it d}-wave form, with a maximum superconducting gap of
14 meV. Our results are consistent with a single gap picture for the cuprates.
Furthermore our data on the even more underdoped sample
LaSrCuO also show sharp spectral peaks, even at the
antinode, with a maximum superconducting gap of 26 meV.Comment: Accepted by Phys. Rev. Let
Origins of large critical temperature variations in single layer cuprates
We study the electronic structures of two single layer superconducting
cuprates, TlBaCuO (Tl2201) and
(BiPb)(SrLa)CuO (Bi2201) which
have very different maximum critical temperatures (90K and 35K respectively)
using Angular Resolved Photoemission Spectroscopy (ARPES). We are able to
identify two main differences in their electronic properties. First, the shadow
band that is present in double layer and low T single layer cuprates
is absent in Tl2201. Recent studies have linked the shadow band to structural
distortions in the lattice and the absence of these in Tl2201 may be a
contributing factor in its T.Second, Tl2201's Fermi surface (FS)
contains long straight parallel regions near the anti-node, while in Bi2201 the
anti-nodal region is much more rounded. Since the size of the superconducting
gap is largest in the anti-nodal region, differences in the band dispersion at
the anti-node may play a significant role in the pairing and therefore affect
the maximum transition temperature.Comment: 6 pages, 5 figures,1 tabl
Anomalies in the Fermi surface and band dispersion of quasi-one-dimensional CuO chains in the high-temperature superconductor YBa2Cu4O8
We have investigated the electronic states in quasi one dimensional (1D) CuO
chains by microprobe Angle Resolved Photoemission Spectroscopy. We find that
the quasiparticle Fermi surface consists of six disconnected segments,
consistent with recent theoretical calculations that predict the formation of
narrow, elongated Fermi surface pockets for coupled CuO chains. In addition, we
find a strong renormalization effect with a significant kink structure in the
band dispersion. The properties of this latter effect [energy scale (~40 meV),
temperature dependence and behavior with Zn-doping] are identical to those of
the bosonic mode observed in CuO2 planes of high temperature superconductors,
indicating they have a common origin.Comment: accepted in Phys. Rev. Let
Anisotropic quasiparticle scattering rates in slightly underdoped to optimally doped high-temperature \LSCO\ superconductors
An angle-resolved photoemission study of the scattering rate in the
superconducting phase of the high-temperature superconductor \LSCO\ with
and , as a function of binding energy and momentum, is
presented. We observe that the scattering rate scales linearly with binding
energy up to the high-energy scale eV. The scattering rate is
found to be strongly anisotropic, with a minimum along the (0,0)-()
direction. A possible connection to a quantum-critical point is discussed.Comment: Final version published in PR
Field-induced soft-mode quantum phase transition in LaSrCuO
Inelastic neutron-scattering experiments on the high-temperature
superconductor LaSrCuO reveal a magnetic excitation
gap that decreases continuously upon application of a magnetic field
perpendicular to the CuO planes. The gap vanishes at the critical field
required to induce long-range incommensurate antiferromagnetic order, providing
compelling evidence for a field-induced soft-mode driven quantum phase
transition
Utilisation de la diffusion des neutrons dans l’étude des mécanismes microscopiques à l’origine de la supraconductivité
La supraconductivité non conventionnelle est certainement l’un des phénoménes les plus remarquables associés à la physique des systémes dits à fortes corrélations électroniques. Dans ces systémes, les degrés de liberté du spin et de la charge de l’électron sont trés fortement couplés, de sorte que le déplacement des charges est contraint par l’environnement magnétique formé par leurs spins. La diffusion inélastique des neutrons est l’unique sonde expérimentale permettant de photographier l’état magnétique de ces systémes dans tout l’espace réciproque et de suivre son évolution sur une échelle d’énergie parfaitement adaptée à celle de la supraconductivité. A travers l’exemple des cuprates supraconducteurs haute température critique, nous montrons comment la diffusion inélastique des neutrons apporte des informations uniques permettant de comprendre l’organisation électronique de ces systèmes à l’échelle microscopique et les mécanismes mise en jeu dans l’apparition de la supraconductivté