Dynamics of the Lattice Array Formation in Superfluid Helium

In 1955, Feynman theorized that the lowest energy state of rotating superfluid helium would result in a lattice structure of quantized vortices. In 1979, Yarmchuk \textit{et. al.} observed a small lattice array of up to eleven vortices using clusters of ions, and later experiments observed the lattice array in superfluid $^{4}$He perpendicular to the axis of rotation using hydrogen ice particles (Bewley \textit{et. al.} 2006). Yet, the formation and dynamics of these arrays remain otherwise unexplored experimentally. Now, by visualizing sub-micron particles trapped on quantized vortices, we characterize the lattice array formation in superfluid helium. Our study investigates the lattice formation by independently varying rotation rate and temperature.