Abstract. -We describe single electron tunneling through molecular structures under the influence of nano-mechanical excitations. We develop a full quantum mechanical model, which includes charging effects and dissipation, and apply it to the vibrating C60 single electron transistor experiment by Park et al. [Nature 407, 57 (2000)]. We find good agreement and argue vibrations to be essential to molecular electronic systems. We propose a mechanism to realize negative differential conductance using local bosonic excitations.Introduction. Experiments on electronic transport through nano-scale systems show a variety of physical conduction mechanisms. Due to their small size quantum mechanics becomes important and Coulomb blockade, interference, and Kondo physics are observed. Molecular systems [1][2][3][4][5][6][7][8] are characterized by large electronic energies beyond room temperature and therefore offer the possibility to measure positions of molecular orbitals by transport spectroscopy. Furthermore, mechanical degrees of freedom in molecules have energies of order 1 − 10 meV which can be probed experimentally for temperatures in the Kelvin regime. This letter addresses the latter topic and combines nano-electronic with nano-mechanical properties, in particular we model the experiment in Ref. [9]. We find that local bosonic excitations have an important influence on single electron tunneling, and thus need to be included in models for molecular electronics. Based on those systems we propose another way to realize negative differential conductance (NDC).Attempts to model transport through molecular nano structures up to now focused more on the electronic structure [10]. In this letter we go one step further and include molecular vibrations (or any other local bosonic excitation) as well. We remark that our approach is fundamentally different from models where the vibration serves as a shuttle for the electrons [11,12]. We address the case where the vibrational frequency is several orders of magnitude larger than the frequency associated with tunneling events. Moreover the physics is dominated

PACS. 72.20.Pa -Thermoelectric and thermomagnetic effects. PACS. 72.15.Qm -Scattering mechanisms and Kondo effect. PACS. 73.23.Hk -Coulomb blockade; single-electron tunneling.Abstract. -In this Letter we study thermoelectric effects in ultra small quantum dots. We study the behaviour of the thermopower, Peltier coefficient and thermal conductance both in the sequencial tunneling regime and in the regime where Kondo correlations develope. Both cases of linear response and non-equilibrium induced by strong temperature gradients are considered. The thermopower is a very sensitive tool to detect Kondo correlations. It changes sign both as a function of temperature and temperature gradient. We also discuss violations of the Wiedemann-Franz law.

We study spectral and transport properties of interacting quantum dots with spin. Two particular model systems are investigated: Lateral multilevel and two parallel quantum dots. In both cases different paths through the system can give rise to interference. We demonstrate that this strengthens the multilevel Kondo effect for which a simple two-stage mechanism is proposed. In parallel dots we show under which conditions the peak of an interference-induced orbital Kondo effect can be split.

Using renormalization group techniques, we study spectral and transport properties of a spinless interacting quantum dot consisting of two levels coupled to metallic reservoirs. For strong Coulomb repulsion U and an applied Aharonov-Bohm phase φ, we find a large direct tunnel splitting |∆| ∼ (Γ/π)| cos(φ/2)| ln(U/ωc) between the levels of the order of the level broadening Γ. As a consequence we discover a many-body resonance in the spectral density that can be measured via the absorption power. Furthermore, for φ = π, we show that the system can be tuned into an effective Anderson model with spin-dependent tunneling.