Colman, R.H.; (2011) Experimental investigations of S=1/2 kagome magnets: the search for quantum spin liquids. Doctoral thesis , UCL (University College London).

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Abstract

The search for quantum spin liquids (QSL) is an enduring problem in condensed matter physics. The QSLs are a broad class of highly correlated ground states that feature large quantum fluctuations. The archetypal of which is the RVB (Resonating Valence Bond) ground state, proposed by Anderson to be the state from which the transition to unconventional superconductivity occurs in the high-Tc cuprates. Since the proposal over 20 years ago that a RVB ground-state may be observable in insulators, experimentalists have been searching for model materials to test the properties of such a ground-state. The geometric frustration of a kagome network of spins, coupled with the high weighting of quantum fluctuations of low spin-state ions is thought to provide the key conditions for such a state to occur. Research in the field has been hindered by the scarcity of materials displaying a kagome network of S=1/2 ions. This thesis details efforts to broaden the library of candidate S=1/2 kagome materials, with the study of four new compounds: `Mg-herbertsmithite', kapellasite, haydeeite and vesignieite. Synthetic conditions, detailed structural studies and preliminary magnetic characterizations of each material are given. While no currently known S=1/2 kagome magnets fully encapsulate the simplicity of the theoretical models, their deviations from ideality can be used as an opportunity to reveal how these perturbations can affect these exotic types of dynamic ground-state. Thereby providing new insight into this quickly expanding fi eld of condensed matter physics

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