3,905 research outputs found
Scanning Tunneling Spectroscopy of Bi2Sr2CuO6+d: New Evidence for the Common Origin of the Pseudogap and Superconductivity
Using scanning tunneling spectroscopy, we investigated the temperature dependence of the quasiparticle density of states of overdoped Bi2Sr2CuO6+δ between 275 mK and 82 K. Below Tc = 10 K, the spectra show a gap with well-defined coherence peaks at ±Δp≃12 meV, which disappear at Tc. Above Tc, the spectra display a clear pseudogap of the same magnitude, gradually filling up and vanishing at T*≃68 K. The comparison with Bi2Sr2CaCu2O8+δ demonstrates that the pseudogap and the superconducting gap scale with each other, providing strong evidence that they have a common origin
Far-infrared absorption and the metal-to-insulator transition in hole-doped cuprates
By studying the optical conductivity of BSLCO and YCBCO, we show that the
metal-to-insulator transition (MIT) in these hole-doped cuprates is driven by
the opening of a small gap at low T in the far infrared. Its width is
consistent with the observations of Angle-Resolved Photoemission Spectroscopy
in other cuprates, along the nodal line of the k-space. The gap forms as the
Drude term turns into a far-infrared absorption, whose peak frequency can be
approximately predicted on the basis of a Mott-like transition. Another band in
the mid infrared softens with doping but is less sensitive to the MIT.Comment: To be published on Physical Review Letter
Nonchiral Edge States at the Chiral Metal Insulator Transition in Disordered Quantum Hall Wires
The quantum phase diagram of disordered wires in a strong magnetic field is
studied as a function of wire width and energy. The two-terminal conductance
shows zero-temperature discontinuous transitions between exactly integer
plateau values and zero. In the vicinity of this transition, the chiral
metal-insulator transition (CMIT), states are identified that are
superpositions of edge states with opposite chirality. The bulk contribution of
such states is found to decrease with increasing wire width. Based on exact
diagonalization results for the eigenstates and their participation ratios, we
conclude that these states are characteristic for the CMIT, have the appearance
of nonchiral edges states, and are thereby distinguishable from other states in
the quantum Hall wire, namely, extended edge states, two-dimensionally (2D)
localized, quasi-1D localized, and 2D critical states.Comment: replaced with revised versio
High frequency and high wavenumber solar oscillations
We determine the frequencies of solar oscillations covering a wide range of
degree (100< l <4000) and frequency (1.5 <\nu<10 mHz) using the ring diagram
technique applied to power spectra obtained from MDI (Michelson Doppler Imager)
data. The f-mode ridge extends up to degree of approximately 3000, where the
line width becomes very large, implying a damping time which is comparable to
the time period. The frequencies of high degree f-modes are significantly
different from those given by the simple dispersion relation \omega^2=gk. The
f-mode peaks in power spectra are distinctly asymmetric and use of asymmetric
profile increases the fitted frequency bringing them closer to the frequencies
computed for a solar model.Comment: Revised version. 1.2 mHz features identified as artifacts of data
analysis. Accepted for publication in Ap
Correlations, inhomogeneous screening, and suppression of spin-splitting in quantum wires at strong magnetic fields
A self-consistent treatment of exchange and correlation interactions in a
quantum wire (QW) subject to a strong perpendicular magnetic field is presented
using a modified local-density approximation (MLDA). The influence of many-body
interactions on the spin-splitting between the two lowest Landau levels (LLs)
is calculated within the screened Hartree-Fock approximation (SHFA), for
filling factor \nu=1, and the strong spatial dependence of the screening
properties of electrons is taken into account. In comparison with the
Hartree-Fock result, the spatial behavior of the occupied LL in a QW is
strongly modified when correlations are included. Correlations caused by
screening at the edges strongly suppress the exchange splitting and smoothen
the energy dispersion at the edges. The theory accounts well for the
experimentally observed strong suppression of the spin-splitting pertinent to
the \nu=1 quantum Hall effect (QHE) state as well as the destruction of this
state in long, quasi-ballistic GaAlAs/GaAs QWs.Comment: Text 23 pages in Latex/Revtex/preprint format, 6 Postscript figures,
submitted to Physical Review
Thermal conductivity of lightly Sr- and Zn-doped LaCuO single crystals
Both ab-plane and c-axis thermal conductivities ( and
) of lightly doped LaSrCuO and
LaCuZnO single crystals ( or = 0 -- 0.04) are
measured from 2 to 300 K. It is found that the low-temperature phonon peak (at
20 -- 25 K) is significantly suppressed upon Sr or Zn doping even at very low
doping, though its precise doping dependences show interesting differences
between the Sr and Zn dopants, or between the plane and the c axis. Most
notably, the phonon peak in decreases much more quickly with Sr
doping than with Zn doping, while the phonon-peak suppression in
shows an opposite trend. It is discussed that the scattering of phonons by
stripes is playing an important role in the damping of the phonon heat
transport in lightly doped LSCO, in which static spin stripes has been observed
by neutron scattering. We also show and data of
LaNdSrCuO and
LaEuSrCuO single crystals to compare with the
data of the lightly doped crystals for the discussion of the role of stripes.
At high temperature, the magnon peak (i.e., the peak caused by the spin heat
transport near the N\'{e}el temperature) in is found to be
rather robust against Zn doping, while it completely disappears with only 1% of
Sr doping.Comment: 7 pages, 4 figures, accepted for publication in Phys. Rev.
High-temperature optical spectral weight and Fermi liquid renormalization in Bi-based cuprates
The optical conductivity and the spectral weight W(T) of two superconducting
cuprates at optimum doping, Bi2Sr2-xLaxCuO6 and Bi2Sr2CaCu2O8, have been first
measured up to 500 K. Above 300 K, W(T) deviates from the usual T2 behavior in
both compounds, even though the zero-frequency extrapolation of the optical
conductivity remains larger than the Ioffe-Regel limit. The deviation is
surprisingly well described by the T4 term of the Sommerfeld expansion, but its
coefficients are enhanced by strong correlation. This renormalization is due to
strong correlation, as shown by the good agreement with dynamical mean field
calculations.Comment: 5 pages, 3 figures, Physical Review Letters in pres
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