Antiferromagnetism and checkerboard charge order in the vortex state
Shou-Cheng Zhang
Dept. of Physics, Stanford University, Stanford, CA 94305
The central issue of high Tc superconductivity is the interplay between antiferromagnetism (AF) and superconductivity (SC). SO(5) theory proposes to unify these two forms of order under a common symmetry principle. In 1997, this theory predicted the AF vortex core in the SC state under a magnetic field. This prediction has now been verified by a number of experiments, including elastic and inelastic neutron scattering, NMR, msR and STM. In this talk, I shall review recent experimental and theoretical progrsses on the AF vortex state. In particular, we will propose a new state in which Cooper pairs forms a checkerboard crystal in a AF background. This state could be realized in underdoped cuprates around the vortex core or above Hc2.
Resonant magnetic mode in high-TC cuprates
Philippe Bourges*
Laboratoire Léon Brillouin, CEA-Saclay, 91191 Gif/Yvette
The spin dynamics of high-TC cuprates measured by inelastic neutron scattering will be discussed. Over the years, these measurements have evidenced a new magnetic excitation present only in the superconducting state. In particular, recent experiments on single layer Tl2Ba2CuO6+d, have been performed near optimum doping ( Tc ~ 90 K) that provide evidence of a sharp magnetic resonant mode below Tc in a very similar way than previous reports on bilayers YBCO and BSCO systems. This result supports models that ascribe a key role to magnetic excitations in the mechanism of superconductivity.
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* Collaborators: Y. Sidis, S. Pailhès (LLB-Saclay), B. Keimer, C. Ulrich, L. Capogna, S. Bayracki (MPI-Stuttgart) L.P. Regnault (CEA-Grenoble),
Comparative Study on the Magnetic Excitation Specta of Y123 and La214 High-Tc Systems - Are the Dynamical Stripes important? -
M. Satoa, M. Itoa, H. Harashinaa, Y. Yasuia, S. Iikuboa, K. Kakuraib
aDepertment of Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602 Japan
bAdvance Science Research Center, JAERI, Tokai, Ibaraki 319-1105 Japan
Neutron data of magnetic excitation spectra c" of YBa2Cu3O6.5 are compared with results of calculations obtained by the expression c(q,w)=c0(q,w)/{ 1+J(q) c0(q,w)}, where J(q)=J(cosqxa + cosqya). Choosing proper values of band parameters and the T-independent gap amplitude with d-wave symmetry, we obtained quite satisfactory agreement between the observed and calculated results without considering dynamical ``stripes". It is found that the broadening at the quasi particles has a role to suppress the antiferromagnetic ordering. Similar studies have also been carried out for La214, where effects of the ``dynamical stripes" can be clearly identified.
Paramagnetic Vortex State in Pr2-xCexCuO4 Single Crystals
Jeff E. Soniera, Ka Fai Poona, Graeme M. Lukeb, Pavlos Kyriakoub, Richard L. Greenec
aDepartment of Physics, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
bDepartment of Physics & Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
cCenter for Superconductivity Research, Department of Physics, University of Maryland, College Park, MD-20742, USA
Muon spin rotation (mSR) measurements of the internal magnetic field distribution in the vortex state of Pr2-xCexCuO4 single crystals are presented. A large increase in the average internal field is observed when the crystals are cooled below Tc. The observation of a paramagnetic shift in the vortex state with a local probe supports models attributing the paramagnetic Meissner effect to currents flowing inside the superconductor. We also report measurements of the in-plane magnetic penetration depth lab for the case where a diamagnetic shift is observed below Tc.