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, LiHoF4, 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.
1 Laboratory for Neutron Scattering, ETH-Zürich and Paul Scherrer Institut, 5232 Villigen, Switzerland.
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
