Magnetic and transport properties of lightly doped La$_{2-x}$Sr$_x$CuO$_4$

We address the problem of the static magnetic correlations in La$_2$CuO$_4$ [1] and lightly doped La$_{2-x}$Sr$_x$CuO$_4$ 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. The helicoidal spin 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$_x$CuO$_4$. 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]. The calculated damping matrix is related to the in-plane resistivity, 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, cond-mat/0502588. [2] V. Juricic, M. B. Silva Neto, and C. Morais Smith, cond-mat/0510312. [3] V. Juricic, L. Benfatto, A. O. Caldeira, and C. Morais Smith, Phys. Rev. Lett. 92, 137202 (2004).