On the Status of Superconductivity-Dependent Friction
Abstract
In order to gain a fundamental understanding of friction, one must understand, at the molecular level, how the energy associated with the work to overcome friction is converted to heat. Such knowledge is key to understanding the rate at which an interface will heat, and in addition how chemical reactions and other physical processes triggered by heat will be affected by friction. One of the simplest possible geometries in which friction can occur, and thus be studied, is that of a fluid or crystalline monolayer adsorbed on an atomically flat surface. This geometry is experimentally accessible to experiments with a Quartz Crystal Microbalance (QCM), to numerical simulation techniques, and to analytic theory. A prior QCM experiment [1] sought to explore the nature of electronic contributions to friction by measuring the friction associated with nitrogen monolayers sliding on Pb substrates, that had been exposed to air, as the temperature passed through the superconducting transition at 7.2K. The work inspired a number of subsequent theoretical and experimental efforts, which yielded contradictory results. We have repeated these measurements on Pb substrates that were prepared in situ for nitrogen, CO and argon films. Argon has been predicted by some theories to exhibit no dependence on the superconducting state of the sample[2] while it has been inferred that CO should exhibit a stronger effect. We present these results and compare them to the current theories of superconductivity-dependent friction. [1] A. Dayo, W. Alnasrallah and J. Krim, Phys. Rev. Lett. vol 80, 1690 (1998); [2] L.W. Bruch, Physical Review B 61, 16201 (2000); Work funded by NSF.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2004
- Bibcode:
- 2004APS..MARN28007H