Long-wavelength fluctuations and anomalous dynamics in 2-dimensional liquids

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 116; no. 46; pp. 22977 - 22982
• Main Authors: Li, Yan-Wei, Mishra, Chandan K., Sun, Zhao-Yan, Zhao, Kun, Mason, Thomas G., Ganapathy, Rajesh, Ciamarra, Massimo Pica
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 12.11.2019
• Subjects: Decoupling; Diffusion coefficient; Divergence; Fluctuations; High temperature; Liquids; Long range order; Physical Sciences; Relaxation time; Wavelength; long-wavelength fluctuations; normal liquid; diffusion; relaxation
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1909319116

In 2-dimensional systems at finite temperature, long-wavelength Mermin–Wagner fluctuations prevent the existence of translational long-range order. Their dynamical signature which is the divergence of the vibrational amplitude with the system size also affects disordered solids and it washes out the transient solid-like response generally exhibited by liquids cooled below their melting temperatures. Through a combined numerical and experimental investigation, here we show that long-wavelength fluctuations are also relevant at high temperature, where the liquid dynamics do not reveal a transient solid-like response. In this regime these fluctuations induce an unusual but ubiquitous decoupling between long-time diffusion coefficient D and structural relaxation time τ, where D ∝ τ–κ, with κ > 1. Long-wavelength fluctuations have a negligible influence on the relaxation dynamics only at extremely high temperatures in molecular liquids or at extremely low densities in colloidal systems.