Emergence, symmetry, and ergodicity breaking in C60 fullerenesLee Liu*

An interacting many-body system can possess qualitatively different properties than those of its microscopic constituents. Examples of such "emergent phenomena" include hydrodynamics, quasi-particles, and phase transitions.

 

Polyatomic molecules comprise a unique class of composite quantum system that hosts emergent phenomena. Molecules feature perfect geometric symmetries and rotate freely in three dimensions. Additionally, they possess a hierarchy of energy scales spanning six orders of magnitude–(nuclear spin interactions), rotational, vibrational, electronic–that enable a spectroscopist to peel back successive layers of emergent behaviour and their underlying physics. This motivates broadband, frequency-domain spectroscopy of gas-phase molecules at the quantum state-resolved limit.

 

Large polyatomic molecules are particularly attractive due to their complexity. However, they typically exhibit intrinsic spectral broadening that precludes quantum state resolution [1]. C_60 is a notable exception: its rigidity and nuclear spin statistics suppresses density of states and allows excited vibrational states to be well-resolved [2].

 

In this talk, I will discuss this perspective on emergence as well as our recent work on C_60 [3]. Infrared spectra showed that C_60 repeatedly breaks and restores rotational ergodicity as it rotates faster and faster. Moreover, the ergodicity breaking occurs without breaking symmetry. This is enabled by the molecule's high degree of symmetry and rich spectrum of vibrations. These insights may be relevant to protecting quantum coherence in complex systems, engineering useful quantum materials, and probing matter out of equilibrium, inspired by the dynamics of non-rigid rotors.

1. Ben Spaun, P. Bryan Changala, David Patterson, Bryce J. Bjork, Oliver H. Heckl, John M. Doyle, and Jun Ye. Nature 533, 517–520 (2016)

2. P. Bryan Changala , Marissa L. Weichman, Kevin F. Lee, Martin E. Fermann, and Jun Ye. Science 363, 49-54 (2019)

3. Lee R. Liu, Dina Rosenberg, P. Bryan Changala, Philip J. D. Crowley, David J. Nesbitt, Norman Y. Yao, Timur V. Tscherbul, and Jun Ye. Science 381, 778-783 (2023)