Direct Observation of Collective Electronuclear Modes about a Quantum Critical Point

  title={Direct Observation of Collective Electronuclear Modes about a Quantum Critical Point},
  author={Matthew Libersky and R. D. McKenzie and Daniel Silevitch and Philip C. E. Stamp and Thomas F. Rosenbaum},
  journal={Physical Review Letters},
We directly measure the low energy excitation modes of the quantum Ising magnet LiHoF4 using microwave spectroscopy. Instead of a single electronic mode, we find a set of collective electronuclear modes, in which the spin-1/2 Ising electronic spins hybridize with the bath of spin-7/2 Ho nuclear spins. The lowest-lying electronuclear mode softens at the approach to the quantum critical point, even in the presence of disorder. This softening is rapidly quenched by a longitudinal magnetic field… 

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