물리학과

Nano-scale junctions consisting of a single molecule or a quantum dot sandwiched between macroscopic metallic leads show a rich variety of non-equilibrium phenomena when exposed to a sufficiently large bias. For example, Coulomb blockade manifests itself in the time-domain as a periodic charging and discharging of the central quantum dot [1]. In this lecture, special attention will be given to the current-induced forces on the nuclei. The real-time dynamics of the system is simulated by combining Ehrenfest dynamics with linear-response time-dependent density functional theory (TDDFT). Electronic viscosity is accounted for by the frequency-dependence of the TDDFT xc kernel. To understand the subtle interplay between the current-induced forces on the nuclei and electronic friction, we study the translational, vibrational, and rotational motion of a diatomic molecule immersed in a current-carrying electron liquid [2]. Starting from the nuclear equilibrium distance and applying a current pulse, we observe three phases of the nuclear motion: (i) acceleration due to the initial dominance of the current-induced force, (ii) stabilization upon balancing of the two forces, and (iii) deceleration caused by the friction after the end of the pulse. Based on these observations, we shall explore the design of an atomic “waterwheel” periodically driven by an AC current imposed on the electron liquid.