Spin Dynamics of the Spin-Ladder Dimer-Chain Material<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>Sr</mml:mi></mml:mrow><mml:mrow><mml:mn>14</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>Cu</mml:mi></mml:mrow><mml:mrow><mml:mn>24</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>O</mml:mi></mml:mrow><mml:mrow><mml:mn>41</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Abstract

We have performed inelastic neutron scattering on a single crystal sample of ${\mathrm{Sr}}_{14}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ to study the spin dynamics of the ${\mathrm{Cu}}_{2}{\mathrm{O}}_{3}$ spin ladder layers and ${\mathrm{CuO}}_{2}$ chains. Our data are best fitted with a dispersion which has a spin gap of $32.5\ifmmode\pm\else\textpm\fi{}0.1\mathrm{meV}$ and a maximum of $193.5\ifmmode\pm\else\textpm\fi{}2.4\mathrm{meV}$, consistent with a coupling along the ladders, ${J}_{\ensuremath{\parallel}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}130\phantom{\rule{0ex}{0ex}}\mathrm{meV}$ and a rung coupling ${J}_{\ensuremath{\perp}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}72\mathrm{meV}$. Excitations with an energy transfer of approximately 11.5 meV arise from a dimer chain with an antiferromagnetic intradimer coupling ${J}_{1}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}11.2\mathrm{meV}$ between next-nearest-neighbor Cu ions, and a ferromagnetic interdimer coupling ${J}_{2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}1.1\mathrm{meV}$. The dimer chains have a periodicity of five units.