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SUMMARY:Tunable Ground States in Two Model Quantum Magnets
DTSTART:20120827T151500
DTSTAMP:20260414T132347Z
UID:72b3177818f9d493b526eb0b68e4c36536e5e801dbbfb9cc92457c00
CATEGORIES:Conferences - Seminars
DESCRIPTION:Dr. Daniel Silevitch\, James Franck Institute\, University of 
 Chicago\nThe ability to control the ground state of a quantum mechanical s
 ystem and tune it across different limits is an important experimental too
 l\, both for manipulating the properties of a system and for studying the 
 associated quantum critical behavior. Here\, we discuss two experimental r
 ealizations of model spin Hamiltonians and show how the ground states can 
 be varied by external tuning mechanisms. The Shastry-Sutherland model\, co
 nsisting of a square lattice of S=1/2 dimerized spins\, has been extensive
 ly studied as a soluble spin system with multiple ground states as a funct
 ion 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 d
 iamond anvil cell tunes the material across a series of ground states. A s
 econd-order quantum phase transition marks the change from the ambient-pre
 ssure\, low temperature configuration of singlets to a plaquette state\, f
 ollowed by a first-order transition to a long-range-ordered antiferromagne
 t [1].  The Transverse-Field Ising Model\, with its interplay between spi
 n interactions and quantum tunneling\, provides a rich laboratory for stud
 ying aspects of basic quantum mechanics. Here\, we focus on the dipole-cou
 pled Ising crystal LiHoxY1-xF4. At x=4.5%\, the equilibrium state of the s
 ystem is shown to depend on the thermodynamic boundary conditions between 
 the crystal and an external heat reservoir\, permitting controllable switc
 hing between states dominated by thermal vs. quantum fluctuations. A simil
 ar selectivity can be achieved by following specific cooling trajectories 
 while using a transverse magnetic field to tune the rate of quantum tunnel
 ing in the material [2].\n\n[1] S. Haravifard et al.\, PNAS 109 2286-2289 
 (2012)\n[2] M. A. Schmidt et al.\, in preparation
LOCATION:PH L1 503 http://plan.epfl.ch/?lang=en&room=PH.L1.503
STATUS:CONFIRMED
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