Two new vortex liquids

In 1967, Reatto and Chester(1) proposed that solid helium-4 might exhibit superfluidity, and in 1970, Leggett(2) suggested what was thought to be a definitive experimental test: to find nonclassical rotational inertia in a toroidal sample. More than three decades later, the observation by Kim and Chan(3,4) of exactly that effect generated great interest and has been repeated and confirmed by a number of groups. However, many attempts to find actual superflow in truly solid samples have failed. Here, I draw an analogy with a second example of anomalous response to vorticity in a dissipative fluid, the vortex liquid phase in the pseudogap region of high-temperature superconductors, and propose that the solid helium experiments have been mischaracterized: what is observed is not supersolidity but an incompressible vortex liquid. This state is distinct from a conventional liquid in that its properties are dominated by conserved supercurrents. owing around a thermally fluctuating tangle of vortices.