Plenarvorträge - DPG-Tagungen

Tiefe Temperaturen Montag
Rbn decreased with x in line with nm enhancements but jcJRbn decreased
also. Reasons for the jcJ and jcJRbn degradations and for the differences
between Ca doped YBCO bicrystal junction and natural junctions in
epitaxial films will be given.
11:00 Pause
TT 2 Supraleitung: Mechanismen, Phasendiagramm, konkurrierende Ordnungen
Zeit: Montag 11:15–12:45 Raum: H20
Hauptvortrag TT 2.1 Mo 11:15 H20
Neutron scattering investigations of high Tc compounds: what
have we learned so far? — •Lothar Pintschovius — Forschungszentrum
Karlsruhe, Institut für Festkörperphysik
High Tc compounds have been very extensively studied by neutron
scattering. The focus has been on elucidating the spin fluctuations because
they are widely considered to mediate high Tc superconductivity.
Nevertheless, the experimental characterization of the magnetic fluctuations
is still full of gaps for important materials. The available data show
that the magnetic excitation spectrum differs profoundly between different
classes of materials. Present theories are usually tailored to explain
the essential features in only one particular class of compounds.
The phonons were found to change not much from the insulating parent
compounds to optimally doped superconductors, with the exception
of the plane polarized Cu-O bond-stretching vibrations. It will be
discussed in how far the electron-phonon coupling effects seen in the
bond-stretching phonons can be linked to anomalies in ARPES spectra
or might be associated with dynamic charge order.
TT 2.2 Mo 11:45 H20
Local Fluctuating Charge Order in the Stripe Ground State
of La1.8−xEu0.2SrxCuO4 — •Hans-Joachim Grafe 1,2 , Nicholas
J. Curro 2 , Markus Hücker 3 , and Bernd Büchner 1 — 1 Leibniz-
Institut für Festkörper- und Werkstoffforschung Dresden, 01171 Dresden,
Germany — 2 Los Alamos National Laboratory, Los Alamos, NM 87545,
USA — 3 Brookhaven National Laboratory, Upton, NY 11973, USA
Nuclear Magnetic Resonance (NMR) studies of the planar oxygen sites
in the cuprate superconductors provides information about both local
spin and charge excitations. Here we report the striking observation of a
strongly temperature dependent electric field gradient (EFG) at the planar
oxygen site in antiferromagnetic stripe ordered La1.8−xEu0.2SrxCuO4,
which stands in stark contrast to the temperature independent result in
superconducting La2−xSrxCuO4materials. Furthermore, measurements of
the spin lattice relaxation rate of the planar oxygen suggest the presence
of glassy charge fluctuations. We interpret these results as the consequence
of inhomogeneously fluctuating charge order associated with the
onset of static stripes.
TT 2.3 Mo 12:00 H20
Dimensionality of magnetic excitations in untwinned YBCO
- an inelastic neutron scattering study — •Vladimir Hinkov 1 ,
Bernhard Keimer 1 , Pailhes Stephane 2 , Bourges Philippe 2 ,
Sidis Yvan 2 , Lin CT 1 , and Kulakov Andrej 1 — 1 MPI für
Festkörperforschung, Stuttgart, Germany — 2 Laboratoire Leon
Brillouin, Saclay, France
Theories trying to describe superconductivity in the high-Tc cuprates
are based on 2D-scenarios of strongly correlated charge carriers. The
CuO2-planes in the LSCO family are unstable against the formation of
1D ”stripes” of antiferromagnetically ordered Cu spins separated by periodically
spaced hole domain walls which should result in an 1D response
TT 3 Spin-Systeme und itinerante Magnete
in inelastic neutron scattering (INS). It is of great significance for theory,
if stripe phases are common for all high-Tc cuprates. Investigation
in YBCO is complicated by twinning - the fact that equal proportions
of twin domains with mutually perpendicular directions of the a*- and
b*-axes exist in the crystal. This automatically leads to a overall 2D response,
even if the separate domains show a 1D response. We present the
world-wide first INS-study of fully twin-free optimally doped YBCO and
demonstrate that the response is still 2D, although a strong anisotropy
between the a*- and b*-axes exist. We give a precise mapping of the
relevant (E,q) space allowing to discriminate between different theories.
TT 2.4 Mo 12:15 H20
Possible isotope effect on the resonance peak formation in high-
Tc cuprates — •Ilya Eremin 1 , Mikhail Eremin 2 , and Oleg Kamaev
2 — 1 Institut für Theoretische Physik, Freie Universität Berlin,
Arnimallee 14, D-14195 Berlin — 2 Physics Department, Kazan State
University, 420008 Kazan, Russian Federation
Within effective t−J Hamiltonian we analyze the influence of electronic
correlations and electron-phonon interaction on the dynamical spin susceptibility
in layered cuprates. We find an isotope effect on the resonance
peak in the magnetic spin susceptibility, Im χ(q, ω), seen by inelastic
neutron scattering. It results from both the electron-phonon coupling
and the electronic correlation effects taken into account beyond random
phase approximation(RPA) scheme. We find at optimal doping the isotope
coeffiecient αres ≈ 0.4 which can be further tested experimentally.
TT 2.5 Mo 12:30 H20
Precursor effects above Tc of the ”ideal” superconducting state
within a phase fluctuation model for the underdoped cuprates
— •Thomas Eckl 1 , Werner Hanke 1 , Enrico Arrigoni 1 , and
Douglas J. Scalapino 2 — 1 Institut für Theoretische Physik und Astrophysik,
Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
— 2 Department of Physics, University of California, Santa Barbara,
CA 93106-9530 USA
The phase fluctuation scenario for the underdoped (UD) cuprates is
based on the idea that the pseudogap originates from phase fluctuations
of a d x 2 −y 2 pairing gap, whose amplitude forms at T MF
c , well above the
actual superconducting (SC) transition at Tc. Recently, we have shown
that a phenomenological model for phase fluctuations can account for different
single-particle properties of the pseudogap state. Here we discuss
precursor effects of the ideal SC state above Tc within our phenomenological
phase fluctuation model. In particular, the paraconductivity and
the fluctuating diamagnetism above Tc in the pseudogap state are analyzed
and the temperature scale at which these effects become visible in
experiment discussed.
[1] T. Eckl, D. J. Scalapino, E. Arrigoni, and W. Hanke, Phys. Rev. B
66, 140510(R) (2002)
[2] T. Eckl, W. Hanke and E. Arrigoni, Phys. Rev. B 68, 014505 (2003)
Zeit: Montag 09:30–13:00 Raum: H18
TT 3.1 Mo 09:30 H18
Is there a spinon-spinon interaction in the Haldane–Shastry
model? — •Dirk Schuricht and Martin Greiter — Institut für
Theorie der Kondensierten Materie, Universität Karlsruhe, 76128 Karlsruhe
Recently, there has been great interest in the dynamics of spinons in
the Haldane–Shastry model, a paradigm for antiferromagnetic spin systems.
Bernevig, Giuliano, and Laughlin [1] have presented arguments for
the existence of a short-ranged, attractive interaction between the spinon
excitations in this model. We reexamine their analysis and conclude that
their interpretation is not correct; the spinon excitations in the Haldane–
Shastry model do not interact. The spinons rather represent an ideal gas
of half-fermions.
[1] B. A. Bernevig et al., Phys. Rev. Lett. 86, 3392 (2001).