Low-energy spin dynamics in La$_{1.95}$Sr$_{0.05}$CuO$_4$*

The low energy part of spin fluctuation spectra $S({\bf q},E)$ of La$_{1.95}$Sr$_{0.05}$CuO$_4$ were measured using the cold neutron triple-axis spectrometer SPINS from 1.5 to 80 K. The incommensurate doublets of magnetic peaks show a tendency to move towards the commensurate (pi,pi) point with increasing energy, like the incommensurate quartets in (La,Ba)$_2$CuO$_4$ and other related cuprates. There is an energy-resolution limited ``central peak'' at $E=0$ below ~20K in the spectra $S({\bf q},E)$, likely due to the spin-glass transition [1]. The inelastic component has a different temperature dependence from the ``central peak'' and a detailed quantitative description of the data becomes available. The {\em local} spectra $S(E)$ behave in a manner closely resembling those of Li-doped La$_{2}$CuO$_4$ [2].\\ \,[1] Y. Chen et al., Phys. Rev. B {\bf 72}, 184401 (2005).\\ \,[2] W. Bao et al., Phys. Rev. Lett. {\bf 91}, 127005 (2003); Y. Chen et al., cond-mat/0408547.