In simple fluids, such as water, invariance under parity and time-reversal symmetry imposes that the rotation of constituent ‘atoms’ is determined by the flow and that viscous stresses damp motion. Activation of the rotational degrees of freedom of a fluid by spinning its atomic building blocks breaks these constraints and has thus been the subject of fundamental theoretical interest across classical and quantum fluids. However, the creation of a model liquid that isolates chiral hydrodynamic phenomena has remained experimentally elusive. Here, we report the creation of a cohesive two-dimensional chiral liquid consisting of millions of spinning colloidal magnets and study its flows. We find that dissipative viscous ‘edge-pumping’ is a key and general mechanism of chiral hydrodynamics, driving unidirectional surface waves and instabilities, with no counterpart in conventional fluids. Spectral measurements of the chiral surface dynamics suggest the presence of Hall viscosity, an experimentally elusive property of chiral fluids. Precise measurements and comparison with theory demonstrate excellent agreement with a minimal chiral hydrodynamic model, paving the way for the exploration of chiral hydrodynamics in experiment.
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We would like to acknowledge discussions with P. Wiegmann, A. Abanov, V. Vitelli and A. Souslov. We also thank M. Fruchart for discussions and pointing us to the review of kinetic theory of Hall viscosity presented in the supplementary information of ref. 46. We finally thank J. Simon for designing our current control circuits and R. Morton for the rendering in Fig. 1b. This work was primarily supported by the University of Chicago Materials Research Science and Engineering Center, which is funded by the National Science Foundation under award number DMR-1420709. Additional support was provided by NSF EFRI NewLAW grant 1741685 and the Packard Foundation. M.J.S. acknowledges the support from NSF grants DMR-1420073 (NYU-MRSEC) and DMS-1463962. S.S. acknowledges support from NSF award DMR-1653465. D.B. and W.T.M.I. gratefully acknowledge the Chicago-France FACCTS programme. The Chicago MRSEC (US NSF grant DMR 1420709) is also gratefully acknowledged for access to its shared experimental facilities.
The authors declare no competing interests.
Peer review information Nature Physics thanks Petia Vlahovska and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Supplementary Information, Figs. 1–26 and refs. 1–21.
From spinning colloidal particles to a chiral fluid.
Particle tracers in the chiral spinner fluid.
Two clusters coalesce.
A droplet impacts a hard wall.
Flow past a circular obstacle.
Surface waves in a chiral spinner fluid.
Droplet intensity in time.
Velocity field in a droplet.
A droplet of chiral fluid on a low-friction substrate.
A hydrodynamic instability.
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Soni, V., Bililign, E.S., Magkiriadou, S. et al. The odd free surface flows of a colloidal chiral fluid. Nat. Phys. 15, 1188–1194 (2019). https://doi.org/10.1038/s41567-019-0603-8
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