Is supersolidity a real effect?

Nature: At low temperatures and high pressure, helium completely solidifies, or does it? In 2004 Eun-Seong Kim and Moses Chan of the Pennsylvania State University found evidence of a phase within frozen He that appeared to flow through the solid like a liquid. Since their experiment, the nature of "supersolidity" has been unresolved: Is it a true many-body quantum phenomenon or is it the result of imperfections in the solid? Nature's Eugenie Samuel Reich reports on recent experiments that might resolve the question.