Aspects of Quantum Magnetism in Quasi One-Dimensional Materials

When: Wednesday, December 19, 2012 at 4:00 pm
Where: DA 114
Speaker: Francesco Casola
Organization: ETH, Zurich and Paul Scherrer Institute
Sponsor: Physics Colloquium

“Quantum effects are known to be particularly effective in magnets with both low spin and dimensionality. In particular, at the core of twenty years of intense experimental and theoretical work on spin-1/2 quasi-1D materials is the fact that spin physics cannot be directly addressed in terms of either a bosonic or fermionic language, although often it entails properties of both these worlds. A broad range of different phenomena thus appears to be surprisingly present even in electronic insulators, such as BEC, Bose-glasses, Luttinger liquids (LL), Wigner crystallization and asymptotic freedom. Investigating these phenomena in spin systems provides both the possibility of tuning the Hamiltonian via an applied field, pressure or through chemical substitution and, at the same time, to use well established techniques for probing magnetic properties as, for instance, nuclear magnetic resonance (NMR) and neutron scattering (NS).

Examples of such a rich physics will be discussed starting from the possibility of observing, via NS, the separation of spin- and charge-degrees of freedom in the LL phase of the model organic spin ladder material (C5D12N)2CuBr4. Next, the effects of disorder in an LL will be discussed by studying via NMR the local magnetism of BaCu2(Si1−xGex)2O7 for x = 0.5. Finally, an attempt of using the BEC paradigm for the understanding of the recently observed field-induced magnetic order in BiCu2PO6 will be made. The latter is a two-leg ladder system with strong geometric frustration of the exchange interactions. Contrary to expectations, supported by high-fields (up to μ0H = 31 T) NMR results and by numerical calculations, we will present indications for a fractionalization of the bosonic-like particles involved in the field-induced order.”

Host: Assistant Professor Adrian Feiguin