1,650 research outputs found
The change of Fermi surface topology in Bi2Sr2CaCu2O8 with doping
We report the observation of a change in Fermi surface topology of
Bi2Sr2CaCu2O8 with doping. By collecting high statistics ARPES data from
moderately and highly overdoped samples and dividing the data by the Fermi
function, we answer a long standing question about the Fermi surface shape of
Bi2Sr2CaCu2O8 close to the (pi,0) point. For moderately overdoped samples
(Tc=80K) we find that both the bonding and antibonding sheets of the Fermi
surface are hole-like. However for a doping level corresponding to Tc=55K we
find that the antibonding sheet becomes electron-like. This change does not
directly affect the critical temperature and therefore the superconductivity.
However, since similar observations of the change of the topology of the Fermi
surface were observed in LSCO and Bi2Sr2Cu2O6, it appears to be a generic
feature of hole-doped superconductors. Because of bilayer splitting, though,
this doping value is considerably lower than that for the single layer
materials, which again argues that it is unrelated to Tc
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
Phenomenological theory of the underdoped phase of a high-T superconductor
We model the Fermi surface of the cuprates by one-dimensional nested parts
near and and unnested parts near the zone diagonals.
Fermions in the nested regions form 1D spin liquids, and develop spectral gaps
below some , but superconducting order is prevented by 1D phase
fluctuations.
We show that the Josephson coupling between order parameters at and
locks their relative phase at a crossover scale . Below
, the system response becomes two-dimensional, and the system displays
Nernst effect. The remaining total phase gets locked at , at
which the system develops a (quasi-) long-range superconducting order.Comment: 4 pages, 1 figure; typos corrected, references adde
Photoemission and the Origin of High Temperature Superconductivity
The condensation energy can be shown to be a moment of the change in the
occupied part of the spectral function when going from the normal to the
superconducting state. As a consequence, there is a one to one correspondence
between the energy gain associated with forming the superconducting ground
state, and the dramatic changes seen in angle resolved photoemission spectra.
Some implications this observation has are offered.Comment: 4 pages, M2S conference proceeding
Destroying coherence in high temperature superconductors with current flow
The loss of single-particle coherence going from the superconducting state to
the normal state in underdoped cuprates is a dramatic effect that has yet to be
understood. Here, we address this issue by performing angle resolved
photoemission spectroscopy (ARPES) measurements in the presence of a transport
current. We find that the loss of coherence is associated with the development
of an onset in the resistance, in that well before the midpoint of the
transition is reached, the sharp peaks in the ARPES spectra are completely
suppressed. Since the resistance onset is a signature of phase fluctuations,
this implies that the loss of single-particle coherence is connected with the
loss of long-range phase coherence.Comment: 7 pages, 7 figure
Self-energy of a nodal fermion in a d-wave superconductor
We re-consider the self-energy of a nodal (Dirac) fermion in a 2D d-wave
superconductor. A conventional belief is that Im \Sigma (\omega, T) \sim max
(\omega^3, T^3). We show that \Sigma (\omega, k, T) for k along the nodal
direction is actually a complex function of \omega, T, and the deviation from
the mass shell. In particular, the second-order self-energy diverges at a
finite T when either \omega or k-k_F vanish. We show that the full summation of
infinite diagrammatic series recovers a finite result for \Sigma, but the full
ARPES spectral function is non-monotonic and has a kink whose location compared
to the mass shell differs qualitatively for spin-and charge-mediated
interactions.Comment: 4pp 3 eps figure
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