Tunable Ground States in Two Model Quantum Magnets
Event details
| Date | 27.08.2012 |
| Hour | 15:15 |
| Speaker | Dr. Daniel Silevitch, James Franck Institute, University of Chicago |
| Location | |
| Category | Conferences - Seminars |
The ability to control the ground state of a quantum mechanical system and tune it across different limits is an important experimental tool, both for manipulating the properties of a system and for studying the associated quantum critical behavior. Here, we discuss two experimental realizations of model spin Hamiltonians and show how the ground states can be varied by external tuning mechanisms. The Shastry-Sutherland model, consisting of a square lattice of S=1/2 dimerized spins, has been extensively studied as a soluble spin system with multiple ground states as a function of the ratio of the inter- and intra-dimer couplings. We show that in the experimental realization SrCu2(BO3)2 the magnetic state is observable via high-resolution X-ray diffraction and that hydrostatic pressure in a diamond anvil cell tunes the material across a series of ground states. A second-order quantum phase transition marks the change from the ambient-pressure, low temperature configuration of singlets to a plaquette state, followed by a first-order transition to a long-range-ordered antiferromagnet [1]. The Transverse-Field Ising Model, with its interplay between spin interactions and quantum tunneling, provides a rich laboratory for studying aspects of basic quantum mechanics. Here, we focus on the dipole-coupled Ising crystal LiHoxY1-xF4. At x=4.5%, the equilibrium state of the system is shown to depend on the thermodynamic boundary conditions between the crystal and an external heat reservoir, permitting controllable switching between states dominated by thermal vs. quantum fluctuations. A similar selectivity can be achieved by following specific cooling trajectories while using a transverse magnetic field to tune the rate of quantum tunneling in the material [2].
[1] S. Haravifard et al., PNAS 109 2286-2289 (2012)
[2] M. A. Schmidt et al., in preparation
[1] S. Haravifard et al., PNAS 109 2286-2289 (2012)
[2] M. A. Schmidt et al., in preparation
Practical information
- Informed public
- Free
Organizer
- ICMP (Arnaud Magrez)
Contact
- Prof. H. Ronnow, LQM