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Low dimensional quantum systems which display collective singlet or spin gap behaviour are of great topical interest due to novelty of the ground states they display. However, while there are many instances of quasi one dimensional spin ladder or chain compounds, there are relatively few good quasi two dimensional experimental examples. SrCu2(BO3)2 is an unusual quantum spin system with a 2D arrangement of spin-1/2 Cu dimers, known to possess a collective singlet ground state. This compound is thought to be the first experimental realisation of the Shastry-Sutherland model. One aspect of the study of SrCu2(BO3)2 for which there is a little information is the influence of impurities on the nature of the singlet ground state. This is due to the relative difficulty of growing high quality single crystals of doped SrCu2(BO3)2. There is much interest in such studies due to the remarkable phenomena associated with doping other quasi-two dimensional copper-oxide quantum magnets, with high-temperature superconductivity being the best appreciated example. In this talk I will discuss the neutron scattering studies of single crystals of doped SrCu2-xMgx(BO3)2 and Sr1-xLaxCu2(BO3)2 and compare these results to our neutron scattering measurements on pure SrCu2(BO3)2. Particular emphasis is placed on the lifetimes of the one-triplet excitations as well as the existence of the in-gap spin excitations in the presence of Mg and La impurities.
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The main advantage of combining Brillouin spectroscopy (BS) with high-resolution x-ray diffraction (XRD) techniques is the ability to perform simultaneous measurements of velocities and elastic moduli (by Brillouin spectroscopy) and the volume/density (by XRD), independent of any pressure standard. With this unique system, located in the 13BM-D station (GSECARS, APS), it is now possible to study materials with BS and XRD in-situ at high pressure-temperature conditions that provide information essential for interpreting seismic observations and constraining models of the composition and evolution of the Earth. Although the system is designed to be very user-friendly, successful BS measurements at high pressure using diamond anvils requires special preparation and a thorough understanding of the peculiarities of the on-line high pressure BS technique. To help our users make the best use of this exceptional technique, we are organizing this COMPRES/GSECARS-supported workshop focusing on the major topics relevant to high pressure research using Brillouin spectroscopy combined with high-resolution x-ray diffraction techniques.
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