Detection of the Mechanical Friction Caused by Electron Systems
Hiroshi Yamaguchi1, Hajime Okamoto1, Sunao Ishihara2, and Yoshiro Hirayama1,3
1Physical Science Laboratory, 2University of Tokyo, 3Tohoku University
Novel methods for investigating the electron behavior in low-dimensional semiconductor structures have been recently developed by integrating these structures into micro/nanomechanical systems. Using the methods, remarkable strain effects on transport properties  and the electron magnetization have been studied. We integrated a high mobility two-dimensional electron system (2DES) in micromechanical cantilevers to study the strain effect on magnetotransport properties in the quantum Hall regime. In addition to the remarkable strain effect at the localized-delocalized electronic state transition, we detected electron-induced internal friction against the cantilever motion with the help of the high mechanical performance of the single crystalline cantilever .
A 2DES Hall bar with low-temperature mobility of 2.4×106 cm2/Vs was integrated near the clamping point of a 200-µm long and 60-µm wide cantilever with the thickness of 1.3 µm (Fig.1). Using a piezoelectric ceramic to drive the cantilever mechanical motion, the induced resistance change was measured as a function of magnetic field. The obtained ‘magnetopiezoresistance’ curve showed a strongly enhanced piezoresistance at the transition between the localized and delocalized electronic states. We obtained a maximum piezoresistive gauge factor of as much as 25,000 near the ν=4 transition.
We found that the cantilever mechanical motion is affected by friction exerted by the electron system, demonstrating its availability for studying the electron energy dissipation. The quality factor of mechanical resonance strongly depended on the applied magnetic field; the value was about 106 near the localized states but only 3×105 for fully delocalized states, indicating the suppression of electron energy dissipation by electron localization (Fig. 2). The strong coupling of the mechanical and electronic degrees of freedom in such integrated structures provides us with a novel method with which to undertake a detailed study of electron behavior in low-dimensional semiconductor structures.
This work was partly supported by Japan Society for the Promotion of Science (JSPS) KAKENHI (16206003).
 H. Yamaguchi, et al., Appl. Phys. Lett. 86 (2005) 052106.
 H. Yamaguchi, et al., Jpn. J. Appl. Phys. 46 (2007) L658.
Fig. 1. Fabricated cantilever structure.
Fig. 2. Mechanical resonance.
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