ORAL SESSION 2CL3: Late News
Tuesday, Feb. 22, 3:30 p.m. – 6:00 p.m., Room 302A (GRB)
Chairs: D. Gubser (Naval Research Lab), J.L. Tholence (CNRS)
2CL3.1 Stripe Formation and Disorder Induced Stripe Fragmentation and Pinning*
V.V. Moshchalkov, L. Trappeniers, and J. Vanacken, Laboratorium voor Vaste-Stoffysica en Magnetisme, K.U.Leuven, Celestijnenlaan 200 D, B-3001 Leuven, Belgium
Presenting Author: V.V. Moshchalkov
We have analyzed the zero field and high field transport properties of several underdoped high-Tc systems. A convincing scaling behavior has been found for all of them, thus proving that the underlying scattering mechanism remains the same as we approach the metal-insulator transition from the metallic side. The scaling temperature To(x) grows substantially with the decreasing hole concentration x. We associate To with the opening of the spin-gap in the spin-ladders appearing due to the stripe formation. Three distinctly different temperature regimes have been identified: (i) high temperature Heisenberg-like 2D regime; (ii) intermediate temperature 1D stripe regime; and (iii) low temperature disorder induced stripe fragmentation and pinning with the enhanced inter fragments and inter-stripe hole hopping, which recovers an effective 2D weak localization logarithmic behavior of resistivity with temperature. The third regime has been revealed by suppressing superconductivity in fields up to 60 T. Hall conductivity data are used to estimate the evolution of the stripe "order parameter" with temperature.
*Supported by the FWO-Vlaanderen, IWT, GOA and IUAP Programs.
2CL3.3 Microwave Absorption Peaks: Signatures of Charge Dynamics in Cuprate Superconductors
Srinivas Sridhar, Zhiyong Zhai, Patanjali Parimi, and Nazih Hakim, Physics Department, Northeastern University, 360 Huntington Avenue, Boston, MA 02115
Presenting Author: S. Sridhar
We present new results and analysis of the microwave response of cuprate superconductors and related oxide materials. A common result observed is the presence of peaks in the temperature dependent microwave absorption. We have observed such peaks in superconducting (T < Tc in Y:123 and Hg:1223), metallic or pseudo-gap (T > Tc in Hg:1201 and underdoped YBCO) and insulating (Sr14Cu24O41 and La5/3Sr1/3NiO4) states. The ubiquitous presence of the peaks clearly indicates that the present explanation of the peaks observed in the superconducting state as due to a competition of relaxation time and quasiparticle density is incorrect, and instead strongly suggests that thy have a non-quasiparticle origin. In La5/3Sr1/3NiO4 the peaks are clearly associated with stripe formation. The similarity of the absorption peaks suggests that stripes may also be responsible for the microwave data observed in the HTS. Excellent quantitative agrement with experimental data is demonstrated using a surprisingly simple description of the charge dynamics.
Work performed in collaboration with Z. Zhai, P.V. Patanjali, N. Hakim, C. Kusko (Northeastern), A. Erb (U. of Geneva), A. Revcolevschi (U.Paris-Sud, Orsay), S. Cheong (Rutgers University), A. Maignan (Caen) and D. Colson (Saclay).
Work supported by NSF, AFOSR and ONR.
2CL3.4 New reentrant superconducting-normal transition in Sr1-xKxBiO3 superconductor: magnetotransport and magnetization study
D.C. Kim 1, J.S. Kim 1, S.J. Joo 1, G.T. Kim 1, C. Bougerol-Chaillout 2, S.M. Kazakov 3, J.S. Pshirkov 3, E.V. Antipov 3, and Y.W. Park 1. 1 Department of Physics and Condensed Matter Research Institute, Seoul National University, Seoul 151-742, Korea. 2 Laboratoire de Cristallographie, CNRS, BP166, 38042 Grenoble Cedex 9, France. 3 Department of Chemistry, Moscow State University, Moscow 119899, Russia.
Presenting Author: Y.W. Park
We report a new reentrant superconducting-normal transition observed in the Sr1-xKxBiO3 superconductor. In magnetotransport measurement, unlike the previous reports about the reentrant resistive transition where the superconducting region becomes reduced and finally resumes the normal state by increasing the external magnetic field (H) or the current (I), we observed the recovery of superconductivity induced by applying H or increasing I. The dc magnetization measurement shows a gradual decrease of the diamagnetic susceptibility - appearance of the paramagnetic Meissner effect- at low fields (H < 50Oe) in the same temperature range where the reentrant normal resistivity was measured. The sample dependence of the reentrant resistive transition suggests the important role of grain boundaries in our samples. Possible physical origins of the observed reentrant transition found in both magnetotransport and susceptibility measurement will be discussed.
2CL3.5 Penetration Depth Studies With Slow Muons
Christof Niedermayer, Fakultät für Physik,
University Konstanz, D-78457 Konstanz, Germany
Presenting Author: Christof Niedermayer During the last two decades a variety of techniques have been
developed which use polarized positive muons as microscopic probes in
condensed matter research (muon spin rotation, relaxation, resonance, mSR).
The mSR technique to date has been limited to bulk studies of matter due
to the high energy of the positive muon (MeV range), resulting in a
large penetration into the target material.
Low energy muons, which can now be prepared by moderating a
conventional muon beam (with energies ranging from 10 eV to 30 keV),
only penetrate into the surface regions*. Hence they provide a unique tool
for local investigations of properties near surfaces and in thin samples. Here
we report the use of low energy muons to determine the spatial variation of
the field distribution in a flux line lattice which emerges through the
surface
of a superconducting film and to directly measure the penetration of
magnetic field into a thin
YBa2Cu3O7 - film in the Meissner state
(i.e. excluding
flux lines).
These studies are based on the low energy mSR program of E.
Morenzoni and coworkers at the Paul-Scherrer Institute in Villigen
Switzerland and
on the fruitful collaboration with the groups of E.M. Forgan
(Birmingham) and J. Litterst (Braunschweig).
*E. Morenzoni, Th. Prokscha, A. Hofer, B. Matthias, M. Meyberg,
Th. Wutzke, H. Gluckler, M. Birke, J. Litterst, Ch. Niedermayer, G. Schatz,
J. Appl. Phys. 81 (1997) 2240.
2CL3.6 Importance of the crossover-current density for a vortex-glass analysis
Patrick Voss-de Haan, Gerhard Jakob, and Hermann Adrian, Institute of Physics, Johannes Gutenberg-University, D-55099 Mainz, Germany.
Presenting Author: G. Jakob
Recent experimental results obtained from transport measurements on extremely long measurement bridges [1] have questioned the validity of previous vortex glass analyses. For electric field windows restricted to relatively high values of E ³ 10-5 V/m the dynamic exponent of the vortex glass transition z » 6, in agreement with theoretical predictions and previous experimental results. However, for extended windows (down to E £ 10-8 V/m) – while the characteristics of a vortex glass transition are preserved – all analyses unambiguously result in z » 9.
In light of this observation the question remains in how far the value of z may further increase for data taken at still lower electric fields. The glass scaling analysis of current-voltage characteristics and the Vogel-Fulcher analysis of resistive transitions both already strongly support the notion that z does not increase any further. A combined analysis of the crossover-current density J0 and crossover-electric field E0 , limiting the critical regime of the vortex glass transition, generally allows a conclusive determination of z dependent primarily on higher electric-field data.
[1] P. Voss-de Haan, G. Jakob, H. Adrian, Phys. Rev. B60, 12443 (1999).