Magnetism of non-magnetic quantum magnets
Event details
| Date | 07.12.2009 |
| Hour | 16:15 |
| Speaker | Prof. Dr. Andrey Zheludev |
| Location |
Auditoire CE 4 - Centre Est
|
| Category | Conferences - Seminars |
The ground state of certain magnetic materials is totally disordered due to zero-point quantum spin fluctuations. Excitations in such "quantum spin liquids" are strongly interacting magnons. Under appropriate conditions these quasiparticles demonstrate all the fundamental properties of quantum Bose fluids. They are subject to the same type of interactions, which may lead to peculiar instabilities, similar to the roton spectrum termination in superfluid 4He, strong finite-T effects due to mutual scattering, or even a total collapse of quasiparticle states. Obeying the same statistics, quasiparticles in spin liquids go through a sequence of quantum phase transitions between "Mott-insulator" and "superfluid" phases. These can be viewed in terms of Bose-Einstein condensation. However, unlike the conventional BEC order parameter (wave function of the condensate), the magnetic analogue is an experimentally observable physical quantity. Like their counterparts in conventional quantum fluids, quasiparticles in spin liquids are subject to localization by an external random potential. If the disorder is strong enough, or the dimensionality low enough, BEC is preceded by a novel exotic state of bosonic matter, the so-called Bose glass. But spin liquids also demonstrate unique phenomena, such as chiral condensates and Luttinget liquid phases, not realized in most conventional Bose fluids.
Excellent realizations of spin liquids are found in several prototypical magnetic materials, with one- two or three-dimensional spin networks, and with endless possibilities for interaction topologies. Chemical modifications provide opportunities to tweaking and fine-tuning the spin Hamiltionian and, through it, the properties of quasiparticles. This opens a totally new experimental route to understanding interacting Bosons. Neutron diffraction and inelastic scattering are especially useful, as they provide direct access to the spin correlation functions. The latter are central to a qualitative interpretation of the underlying physics, and are what the theorists typically like to calculate.
In this context, in my talk I will review recent neutron scattering results for several quantum spin ladder and related materials.
Links
Practical information
- General public
- Free