In a recent paper Krim and coworkers have observed that the friction force,
acting on a thin physisorbed layer of N-2 sliding on a lead film, abruptly
decreases by a factor of similar to 2 when the lead film is cooled below i
ts superconductivity transition temperature. I discuss the possible mechani
sms for the abruptness of the friction drop. (C) 2000 Elsevier Science Ltd.
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