906 research outputs found
Can Impurity Effects Help to Identify the Symmetry of the Order Parameter of the Cuprates?
The effects of non-magnetic impurities on the properties of superconductors
with order parameters (OP) of different symmetry are discussed. In particular,
we contrast the case of a d_{x^2 - y^2} with various forms of an anisotropic
s-wave (ASW) gap. The biggest qualitative difference occurs if the phase of the
s-wave OP does not change sign.Comment: 2pages, uuencoded Postscript, to appear in the Proceedings of the
M^2-HTSC IV conferenc
Odd Parity and Line Nodes in Heavy Fermion Superconductors
Group theory arguments have demonstrated that a general odd parity order
parameter cannot have line nodes in the presence of spin-orbit coupling. In
this paper, it is shown that these arguments do not hold on the
zone face of a hexagonal close packed lattice. In particular, three of the six
odd parity representations vanish identically on this face. This has potential
relevance to the heavy fermion superconductor .Comment: 5 pages, revte
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
Tunneling spectra of submicron BiSrCaCuO intrinsic Josephson junctions: evolution from superconducting gap to pseudogap
Tunneling spectra of near optimally doped, submicron
BiSrCaCuO intrinsic Josephson junctions are presented,
and examined in the region where the superconducting gap evolves into
pseudogap. The spectra are analyzed using a self-energy model, proposed by
Norman {\it et al.}, in which both quasiparticle scattering rate and
pair decay rate are considered. The density of states derived
from the model has the familiar Dynes' form with a simple replacement of
by = ( + )/2. The
parameter obtained from fitting the experimental spectra shows a roughly linear
temperature dependence, which puts a strong constraint on the relation between
and . We discuss and compare the Fermi arc behavior
in the pseudogap phase from the tunneling and angle-resolved photoemission
spectroscopy experiments. Our results indicate an excellent agreement between
the two experiments, which is in favor of the precursor pairing view of the
pseudogap.Comment: 7 pages, 6 figure
On the determination of the Fermi surface in high-Tc superconductors by angle-resolved photoemission spectroscopy
We study the normal state electronic excitations probed by angle resolved
photoemission spectroscopy (ARPES) in Bi2201 and Bi2212. Our main goal is to
establish explicit criteria for determining the Fermi surface from ARPES data
on strongly interacting systems where sharply defined quasiparticles do not
exist and the dispersion is very weak in parts of the Brillouin zone.
Additional complications arise from strong matrix element variations within the
zone. We present detailed results as a function of incident photon energy, and
show simple experimental tests to distinguish between an intensity drop due to
matrix element effects and spectral weight loss due to a Fermi crossing. We
reiterate the use of polarization selection rules in disentangling the effect
of umklapps due to the BiO superlattice in Bi2212. We conclude that, despite
all the complications, the Fermi surface can be determined unambiguously: it is
a single large hole barrel centered about (pi,pi) in both materials.Comment: Expanded discussion of symmetrization method in Section 5, figures
remain the sam
Calculation of Effective Coulomb Interaction for , , and
In this paper, the Slater integrals for a screened Coulomb interaction of the
the Yukawa form are calculated and by fitting the Thomas-Fermi wavevector, good
agreement is obtained with experiment for the multiplet spectra of
and ions. Moreover, a predicted multiplet spectrum for the heavy
fermion superconductor is shown with a calculated Coulomb U of 1.6 eV.
These effective Coulomb interactions, which are quite simple to calculate,
should be useful inputs to further many-body calculations in correlated
electron metals.Comment: 8 pages, revtex, 3 uuencoded postscript figure
Electron Self-Energy of High Temperature Superconductors as Revealed by Angle Resolved Photoemission
In this paper, we review some of the work our group has done in the past few
years to obtain the electron self-energy of high temperature superconductors by
analysis of angle-resolved photoemission data. We focus on three examples which
have revealed: (1) a d-wave superconducting gap, (2) a collective mode in the
superconducting state, and (3) pairing correlations in the pseudogap phase. In
each case, although a novel result is obtained which captures the essense of
the data, the conventional physics used leads to an incomplete picture. This
indicates that new physics needs to be developed to obtain a proper
understanding of these materials.Comment: 5 pages, revtex, 3 encapsulated postscript figures, SNS97 proceeding
Transport and the Order Parameter of Superconducting UPt3
We calculate the ultrasonic absorption and the thermal conductivity in the
superconducting state of UPt as functions of temperature and direction of
propagation and polarization. Two leading candidates for the superconducting
order parameter are considered: the and representations. Both
can fit the data except for the ultrasonic absorption in the phase. To do
that, it is necessary to suppose that the system has only a single domain, and
that must be chosen as the most favorable one. However, the theory
requires fine-tuning of parameters to fit the low temperature thermal
conductivity. Thus, transport data favor the theory. Measurements of
the thermal conductivity as a function of pressure at low temperature could
help to further distinguish the two theories.Comment: 7 pages, 4 figure
Fermi edge singularities in X-ray spectra of strongly correlated fermions
We discuss the problem of the X-ray absorption in a system of interacting
fermions and, in particular, those features in the X-ray spectra that can be
used to discriminate between conventional Fermi-liquids and novel "strange
metals". Focusing on the case of purely forward scattering off the core-hole
potential, we account for the relevant interactions in the conduction band by
means of the bosonization technique. We find that the X-ray Fermi edge
singularities can still be present, although modified, even if the density of
states vanishes at the Fermi energy, and that, in general, the relationship
between the two appears to be quite subtle.Comment: Latex, 16 pages, Princeton preprin
Magnetic Collective Mode Dispersion in High Temperature Superconductors
Recent neutron scattering experiments in the superconducting state of YBCO
have been interpreted in terms of a magnetic collective mode whose dispersion
relative to the commensurate wavevector has a curvature opposite in sign to a
conventional magnon dispersion. The purpose of this article is to demonstrate
that simple linear response calculations are in support of a collective mode
interpretation, and to explain why the dispersion has the curvature it does.Comment: 3 pages, revtex, 4 encapsulated postscript figure
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