Exchange interaction and Fano resonances in diatomic molecular systems

We propose a mechanism to use scanning tunneling microscopy (STM) for direct measurements of the two-electron singlet-triplet exchange splitting $J$ in diatomic molecular systems, unsing the coupling between the molecule and the substrate electrons. The different pathways for electrons lead to interference effects and generate kinks in the differential conductance at the energies for the singlet and triplet states. These features are related to Fano resonance due to the branched electron wave functions. The ratio between the tunneling amplitudes through the two atoms can be modulated by spatial movements of the tip along the surface.Comment: 4 pages, 2 figures, submitted - Changes in Fig. 1 (panel c) added), and minor modification in the main text - new version, as publishe

Detection of exchange interaction in STM measurements through Fanolike interference effects

We address Fano-like interference effects in scanning tunneling microscopy (STM) measurements of nanoscale systems, e.g. two-level systems. Common for these systems is that second order tunneling contributions give rise to interference effects that cause suppressed transmission through the system for certain energies. The suppressed transmission is measurable either in the differential conductance or in the bias voltage derivative thereof.Comment: 9 pages, 3 figures, submitted: in addition to the results published in Phys. Rev. B, 75, 153309 (2007), this paper contains a more thorough discussion on the used transport formalism, studies of asymmetric couplings to the substrate, and discussion of non-resonant levels. The non-resonant case is related to spin-dependent tunnelin

Vibrating Superconducting Island in a Josephson Junction

We consider a combined nanomechanical-supercondcuting device that allows the Cooper pair tunneling to interfere with the mechanical motion of the middle superconducting island. Coupling of mechanical oscillations of a superconducting island between two superconducting leads to the electronic tunneling generate a supercurrent which is modulated by the oscillatory motion of the island. This coupling produces alternating finite and vanishing supercurrent as function of the superconducting phases. Current peaks are sensitive to the superconducting phase shifts relative to each other. The proposed device may be used to study the nanoelectromechanical coupling in case of superconducting electronics.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let