(a) and (c) show the measured one and two magnon data respectively from La4Sr10Cu24O41 with the non-magnetic background subtracted. (b) and (d) show the simulated data. The white curves show the one magnon dispersion curve and the lower boundary of the two magnon dispersion.
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The complete magnetic excitation spectrum of a cuprate compound, measured for the first time.
Cuprate ladders can be thought of as a strip cut out of a 2D square lattice, and therefore provide a link between magnetic behaviour in one and two dimensions. Additionally they share many features of the 2D high-temperature superconducting materials, and when doped and pressurised they become superconducting themselves.
We have investigated the ladder compound La4Sr10Cu24O41 and for the first time measured its complete magnetic excitation spectrum. A special feature of ladders is that the rung coupling decomposes scattering into separate one- and two-magnon contributions.
Utilising a powerful new computational method it has been possible for us to completely describe the quantum dynamics of the ladder. Our findings show not only that cyclic charge fluctuations are important in such systems but that oxygen tunnelling is essential to the description of the magnetic states. Our results provide a foundation for understanding strongly correlated states in this model cuprate.
S Notbohm, DA Tennant (University of St Andrews), B Lake (University of Oxford), R Bewley, P Manuel (ISIS), P Ribeiro (IFW-Dresden, Germany), RS Eccleston (Sheffield Hallam University) and CD Frost (ISIS)
Research date: December 2006
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