.
\nSupersolids and superfluids rank among the most exotic of quantum mechanical phenomena.
\nSuperfluids can flow without any viscosity, and experience no friction as they flow along the walls of
\na container, because their atoms \u2018condense\u2019 into a highly coherent state of matter. Supersolids are
\nalso characterized by coherent effects, but between vacancies in a crystal lattice rather than between
\nthe solid\u2019s atoms themselves.
\n.
\nThe reduction in the rotational inertia of a bar of solid helium-4 as it was cooled to very low temperatures
\nprovided the first experimental evidence for supersolids. Physicists interpreted the reduction to mean
\nthat some amount of supersolid helium had formed and decoupled from the remainder of the bar, affecting
\nits rotational inertia and frequency. Others argued that the reduction in inertia resulted from a change in the
\nhelium\u2019s viscosity and elasticity with temperature, rather than from the onset of supersolidity.
\n.
\nKimitoshi Kono from the RIKEN Advanced Science Institute in Wako, Eunseong Kim from KAIST in Korea, and
\ntheir colleagues from these institutes have now disproved the alternative interpretation by simultaneously
\nmeasuring the shear modulus (a measure of viscosity and elasticity) and the rotational inertia of a solid helium-4
\ncell as its temperature dropped from 1 kelvin to 15 thousandths of a kelvin1. The cell was made to rotate clockwise
\nand then counterclockwise periodically, as well as to rotate clockwise or counterclockwise continuously .
\nThe continuous rotation affected the inertial mass of the helium but its shear modulus, allowing these quantities
\nto be monitored independently.
\n.
\nUnder continuous rotation, the degree of change in the rotational inertia had a clear dependence on rotation velocity
\n, while the shear modulus did not. In addition, the energy dissipated by the rotation increased at high speeds. Both of
\nthese observations contrast to what would be expected if viscoelastic effects were at play, rather than supersolidity.
\nThe researchers also found that periodic rotation and continuous rotation affected the rotation differently, raising new
\nquestions about the experimental system.
\n.
\nThe data support the interpretation that changes in the rotational inertia of helium-4 at low temperature result from
\nsupersolidity. This is important because of the novel and surprising nature of the phenomenon itself, says Kono.
\n\u201cSuperfluidity in a solid is a very radical concept which, if proven, is certainly a good candidate for the Nobel Prize
\n\u201d he adds. \u201cTherefore the first priority is to determine whether it can be proven in a fashion that will convince the
\nlow-temperature physics community.\u201d
\n.<\/p>\n","protected":false},"excerpt":{"rendered":"
. Supersolids and superfluids rank among the most exotic of quantum mechanical phenomena. Superfluids can flow without any viscosity, and experience no friction as they flow along the walls of a container, because their atoms \u2018condense\u2019 into a highly coherent state of matter. Supersolids are also characterized by coherent effects, but between vacancies in a … <\/p>\n