Condensed-Matter Physics & Materials Science Seminar

In the first part of the talk, we will address the problem of the static magnetic correlations in La(2)CuO(4) [1] and lightly doped La(2-x)Sr(x)CuO4 within the framework of a dipolar frustration model for a canted antiferromagnet [2]. We show that the Dzyaloshinskii-Moriya and XY anisotropies are responsible for robustness of the Neel state for x < 2% while, for higher doping, the antiferromagnetic ground state is unstable towards a helicoidal magnetic phase where the transverse components of the staggered magnetization rotate in a plane perpendicular to the orthorhombic b-axis. Such helicoidal structure gives rise to incommensurate peaks in elastic neutron scattering, and is consistent with recent Raman and magnetic susceptibility experiments in La(2-x)Sr(x)CuO4. Finally, we propose the neutron scattering experiment in the magnetic field perpendicular to the CuO(2) planes as the ``smoking gun'' for discriminating between a scenario based on the formation of a helicoid and the diagonal stripe scenario.

In the second part, the transport properties in the spin-glass phase of La(2-x)Sr(x)CuO(4) will be discussed. We propose that the dissipative dynamics of topological defects in a spiral state is responsible for the transport properties in the spin-glass phase of cuprates [3]. Using the collective-coordinate method, we show that topological defects are coupled to a bath of magnetic excitations. By integrating out the bath degrees of freedom, we find that the dynamical properties of the topological defects are dissipative. The calculated damping matrix is related to the in-plane resistivity [4], which exhibits an anisotropy and linear temperature dependence in agreement with experimental data.

References:
[1] M. B. Silva Neto, L. Benfatto, V. Juricic, and C. Morais Smith, Phys. Rev. B 73, xxxxx (2006), cond-mat/0502588.
[2] V. Juricic, M. B. Silva Neto, and C. Morais Smith, cond-mat/0510312, to appear in Phys. Rev. Lett. (2006).
[3] V. Juricic, L.