Europhys. Lett.
Volume 76, Number 2, October 2006
Page(s) 325 - 331
Section Interdisciplinary physics and related areas of science and technology
Published online 13 September 2006
Europhys. Lett., 76 (2), pp. 325-331 (2006)
DOI: 10.1209/epl/i2006-10257-7

Are better conductors more rigid?

Young-Ho Eom1, Hawoong Jeong1, Henri Orland2 and Juyeon Yi3

1  Department of Physics, Korea Advanced Institute of Science and Technology - Daejeon, 305-701, Korea
2  Service de Physique Théorique, CEA-Saclay 91191 Gif-sur-Yvette Cedex, France
3  Department of Physics, Pusan National University - Busan 609-735, Korea

received 21 July 2006; accepted in final form 23 August 2006
published online 13 September 2006

The variation of the bending stiffness of various materials is studied from the point of view of the electronic band characteristics. As far as the electronically generated bending stiffness $\kappa_{e}$ (which we refer to as electro-stiffness) is concerned, the relevant factors are the orbital overlap t, the gap width u between the valence band and the conduction band, and the electron filling fraction $\gamma$. A perturbative calculation leads to the approximate expression $\kappa_{e}\sim t^{2}/\sqrt{u^2+t^{2}}$. This shows that materials with a large overlap and narrow band gap should be stiffer. The electro-stiffness also depends on the electron filling-fraction. We find that $\kappa_{e}(\gamma)\leq
\kappa_{e}(1/2)$. These kinds of behavior are confirmed by numerical calculations. In addition, we study the variation in the projected length of flexible molecules under a voltage bias. The nonlinear variation of the bending rigidity is shown to give rise to a length contraction or dilation, depending on the voltage bias.

82.35.Cd - Conducting polymers.
72.80.Le - Polymers; organic compounds (including organic semiconductors).
77.65.Bn - Piezoelectric and electrostrictive constants.

© EDP Sciences 2006