Ergodicity breaking in rapidly rotating C60 fullerenes

Ergodicity, the central tenet of statistical mechanics, requires an isolated system to explore all available phase space constrained by energy and symmetry. Mechanisms for violating ergodicity are of interest for probing nonequilibrium matter and protecting quantum coherence in complex systems. Polyatomic molecules have long served as a platform for probing ergodicity breaking in vibrational energy transport. Here, we report the observation of rotational ergodicity breaking in an unprecedentedly large molecule, 12C60, determined from its icosahedral rovibrational fine structure. The ergodicity breaking occurs well below the vibrational ergodicity threshold and exhibits multiple transitions between ergodic and nonergodic regimes with increasing angular momentum. These peculiar dynamics result from the molecule’s distinctive combination of symmetry, size, and rigidity, highlighting its relevance to emergent phenomena in mesoscopic quantum systems. Description Editor’s summary Ergodicity breaking, the inability of a system to thermalize, is of fundamental interest in statistical mechanics and physics and has been vigorously studied in many systems. Using high-sensitivity infrared spectroscopy, Liu et al. collected compelling experimental signatures of previously unobserved rotational ergodicity breaking in a buckminsterfullerene molecule (C60) that arose from rotation-vibration coupling and were distinctly different from what was found in all prior studies. Because of its symmetry, size, and rigidity, C60 can switch back and forth between ergodic and non-ergodic rotational regimes as it rotates faster and faster. The present work reports peculiar rotational dynamics in C60 and demonstrates how such a familiar but relatively unexplored molecule can be used to observe new phenomena. —Yury Suleymanov The icosahedral C60 molecule’ s ability to thermalize its rotational degree of freedom can switch on and off as it spins up.