Session 27aC

QED₃ Theory of Pairing Pseudogap in Cuprates

Zlatko Tesanovic

Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA

I review recent progress in understanding the underdoped cuprates by using a fluctuating d-wave superconductor as the point of departure. As the phase order is destroyed by underdoping, the effective theory takes the form of a quantum electrodynamics in (2+1) dimensions (QED₃). The role of Dirac fermions is played by nodal quasiparticles while the gauge field encodes topological frustration felt by quasiparticles in presence of unbound vortex-antivortex fluctuations. In its chirally symmetric phase, the QED₃ effective theory is a non-Fermi liquid, exhibiting anomalous power laws in its fermionic propagators. As one approaches half-filling, this algebraic Fermi liquid (AFL) suffers a spontaneous transition to the chiral symmetry-broken state of QED₃. The chiral symmetry breaking gives rise to an incommensurate antiferromagnetism (SDW), QED₃ stripe phases and other forms of competing insulating states.

Interplay between static magnetism and superconductivity in HTSC cuprates

Yasutomo J. Uemura^a, Andrei T. Savici^a, Graeme M. Luke^b, Kenji M. Kojima^c, Shin-ichi Uchida^c

^aPhysics Department, Columbia University, New York, NY 10027, USA

^bDepartment of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada

^cDepartment of Superconductivity, University of Tokyo, Tokyo 113, Japan

We present our recent results of Muon Spin Relaxation (mSR) studies which reveraled: (1) formation of nano-scale ( ~ 15-30 Å radius) islands with static magnetism in superconducting stage-4 La₂CuO_4.11 [A.T. Savici et al. , PRB66 in press]; (2) trade-off between the volume fraction of static magnetsim and the superfluid density in (La,Eu,Sr)₂CuO₄, which demonstrates that static magnetism and supercnductivity occur in mutually exclusive regions; (3) correlations between T_c and n_s/m^* (superconducting carrier density / effective mass) in these systems with co-existing superconductivity and static magnetism; and (4) field-induced static magnetism existing exclusively in the under-optimally doped region of (La,Sr)₂CuO₄.

Magnetism and superconductivity of La_2-xSr_xCuO₄: The NMR point of view

Marc-Henri Julien

Laboratoire de Spectrometrie Physique, Universite J. Fourier Grenoble, 38042 St Martin d'Heres, France

Recent NMR results showing the coexistence of magnetic order and superconductivity in La_2-xSr_xCuO₄ will be reviewed. The data will be compared to those obtained by other techniques. The glassy nature of magnetic freezing, the existence of inhomogeneities, the influence of a magnetic field, the spin and charge textures are among important questions to be discussed. See Phys. Rev. B 63, 144508 (2001) for an introduction and references.¹

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