Phonon Quantum Phase Transition*

The emergence of novel quantum phenomena is often shown in materials close to a zero temperature phase transition. Much of the effort to study these new effects, like Kondo entanglement and its breakdown in heavy-fermion metals, has been focused mainly in fermionic systems. Here, we demonstrate that a phonon (bosonic) system can exhibit a quantum phase transition with dislocations. The quantum critical point (QCP) reached by the phonons arises at a second-order transition between two-ground states corresponding to a conventional phonon state (symmetric phase) and a dynamically-induced dipole field (symmetry-broken phase), at zero temperature. The distinct ground states arise from a competition between the phonon-dislocation anharmonic interaction and the topological nature of the dislocation. Furthermore, through renormalization group analysis, this phonon system provides a very different type of quantum critically which can be used to tailor phonon transport at the single-mode level [arXiv:1809.06495].