Letter

Nature 449, 1025-1028 (25 October 2007) | doi:10.1038/nature06228; Received 3 July 2007; Accepted 7 September 2007

Probable heat capacity signature of the supersolid transition

X. Lin1, A. C. Clark1 & M. H. W. Chan1

  1. Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA

Correspondence to: M. H. W. Chan1 Correspondence and requests for materials should be addressed to M.H.W.C. (Email: chan@phys.psu.edu).

Liquid 4He enters the superfluid state and flows without friction below 2.176 K. Thin liquid films adsorbed on solid substrates undergo the same transformation, although at a lower temperature. When the substrate is subjected to oscillatory motion a portion of the film, known as the superfluid fraction, decouples from the oscillation. A similar phenomenon has been observed1, 2 in solid 4He, in which a fraction of the solid seems to decouple from the motion of the surrounding lattice. Although this observation has been replicated in various laboratories3, 4, 5, 6, no thermodynamic signature of the possible supersolid transition has been seen. Here we report the finding of a heat capacity peak that coincides with the onset of mass decoupling. This complementary experimental evidence supports the existence of a genuine transition between the normal solid and supersolid phases of 4He.

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