Equilibrium and nonequilibrium fluctuations of nanomechanical oscillator coupled to a tunnel junction

We have analyzed the dynamics of a mechanical oscillator coupled to an electrical tunnel junction with an arbitrary voltage applied to the junction and arbitrary temperature of electrons in leads. We have shown that if the mass of mechanical oscillator is large, there is no oscillator heating until the applied bias voltage exceeds the characteristic oscillator frequency. In the opposite case, coupling to the tunnel junction leads to anharmonicity of the mechanical oscillator even with zero applied bias because of virtual forward and backward tunneling events. Applications of nanoelectromechanical systems to spintronics are discussed.