Quantum Phase Transition of a Magnet in a Spin Bath
H. M. Rønnow,1,2,3*
R. Parthasarathy,2
J. Jensen,4
G. Aeppli,5
T. F. Rosenbaum,2
D. F. McMorrow3,4,6
The excitation spectrum of a model magnetic system, LiHoF
4,
was studied with the use of neutron spectroscopy as the system
was tuned to its quantum critical point by an applied magnetic
field. The electronic mode softening expected for a quantum
phase transition was forestalled by hyperfine coupling to the
nuclear spins. We found that interactions with the nuclear spin
bath controlled the length scale over which the excitations
could be entangled. This generic result places a limit on our
ability to observe intrinsic electronic quantum criticality.
2 James Franck Institute and Department of Physics, University of Chicago, Chicago, IL 60637, USA.
3 Risø National Laboratory, DK-4000 Roskilde, Denmark.
4 Ørsted Laboratory, Niels Bohr Institute fAPG, Universitetsparken 5, 2100 Copenhagen, Denmark.
5 London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, London WC1E 6BT, UK.
6 ISIS, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UK.
* To whom correspondence should be addressed. E-mail: henrik.ronnow{at}psi.ch
