  The heat capacity of the mass selected Na41+ cluster has been measured using
a differential nanocalorimetry method. A two-peak structure appears in the heat
capacity curve of Na41+, whereas Schmidt and co-workers [ M. Schmidt, J.
Donges, Th. Hippler, and H. Haberland, Phys. Rev. Lett. 90, 103401 (2003) ]
observed, within their experimental accuracy, a smooth caloric curve. They
concluded from the absence of any structure that there is a second order
melting transition in Na41+ with no particular feature such as premelting. The
observed difference with the latter results is attributed to the better
accuracy of our method owing to its differential character. The two structures
in the heat capacity are ascribed to melting and premelting of Na41+. The peak
at lower temperature is likely due to an anti-Mackay to Mackay solid-solid
transition.
