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dc.contributor.advisorLee, Stephen
dc.contributor.advisorTennant, David Alan
dc.contributor.authorNotbohm, Susanne
dc.description.abstractThis thesis describes the neutron scattering measurements of magnetic excitations in spin-chains and ladders. The first part discusses an experimental investigation of the copper oxide family Srâ â Cuâ â Oâ â composed of edge-sharing chains and spin-ladders. The study of Laâ Srâ â Cuâ â Oâ â comprises a slightly hole-doped chain and an undoped ladder structure where the chain can be modeled by a ferromagnetic nearest and an antiferromagnetic next-nearest neighbor coupling. The hole effects are apparent in gaps in the dispersion relation and can be described by a charge-density wave agreeing with the commensuration of the dispersion. Investigating the undoped ladder establishes the exchange constants including a cyclic exchange manifested by the two-magnon continuum and the suppression of the S = 1 bound mode. An orbital consideration provides an explanation for the exchanges including the different sizes of rung and leg coupling. The excitation spectrum of the doped ladder in Caâ .â Srâ â .â Cuâ â Oâ â can be described by a direct comparison with the undoped ladder and the differences consisting of a higher energy mode and subgap scattering can be successfully modeled by the charge spectrum of the ladder calculated from the free electron model. The second part of the thesis investigates the alternating chain material Cu(NOâ )â · 2.5D2O and establishes the gapped one-magnon dispersion, the two-magnon continuum and for the first time the S =1 bound mode. Applying magnetic field drives the system through two critical field transitions, condensation of magnons into the ground state and saturation. The modes beyond saturation can be modeled by spin wave theory and the excitations at the first critical field follow Luttinger Liquid behavior. Additionally investigated are the temperature effects with the excitations being of a different nature but containing the signature of a strong correlated system. For an outlook the measurements including temperature and field are provided with further theoretical descriptions necessary.en
dc.format.extent8023999 bytes
dc.publisherUniversity of St Andrews
dc.subjectQuantum magnetsen
dc.subjectQuasi one-dimensional systemen
dc.subjectHole-doping effectsen
dc.subjectStrong correlationen
dc.subject.lcshQuantum field theoryen
dc.subject.lcshNuclear spinen
dc.titleSpin dynamics of quantum spin-ladders and chainsen
dc.type.qualificationnamePhD Doctor of Philosophyen
dc.publisher.institutionThe University of St Andrewsen
dc.publisher.departmentHahn-Meitner-Institute Berlinen

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