Two-electron elastic tunneling in low-dimensional conductors

This article was published in the journal, Physical Review B [© American Physical Society]. It is also available at: http://link.aps.org/abstract/PRB/v65/e155209.We solve the Lippmann-Schwinger equation describing one-dimensional elastic scattering of preformed pairs (e.g., bipolarons) off a short-range scattering center, and find the two-particle transmission through a thin potential barrier. While the pair transmission is smaller than the single-electron transmission in the strong-coupling limit, it is remarkably larger in the weak-coupling limit. We also calculate current-voltage characteristics of a molecule-barrier-molecule junction. They show unusual temperature and voltage behaviors which are experimentally verifiable at low temperatures in bulk and nanoscale molecular conductors

From prescriptive programming of solid-state devices to orchestrated self-organisation of informed matter

Achieving real-time response to complex, ambiguous, high-bandwidth data is impractical with conventional programming. Only the narrow class of compressible input-output maps can be specified with feasibly sized programs. Present computing concepts enforce formalisms that are arbitrary from the perspective of the physics underlying their implementation. Efficient physical realizations are embarrassed by the need to implement the rigidly specified instructions requisite for programmable systems. The conventional paradigm of erecting strong constraints and potential barriers that narrowly prescribe structure and precisely control system state needs to be complemented with a new approach that relinquishes detailed control and reckons with autonomous building blocks. Brittle prescriptive control will need to be replaced with resilient self-organisation to approach the robustness and efficiency afforded by natural systems. Structure-function self-consistency will be key to the spontaneous generation of functional architectures that can harness novel molecular and nano materials in an effective way for increased computational power

Control of the Photochemical Reactivity of Coordination Compounds by Formation of Supramolecular Structures: the Case of Hexacyanocobaltate (III) Anion Associated with Polyammonium Macrocyclic Receptors

The photochemical behavior of free CO(CN) ~a~n-d of the adducts obtained from the association of CO(CN) ~w~it-h diethylammonium ion (Et2NH2+)a, linear plyammonium ion (L-21- N6H2+),a nd three plyammonium macrocycles (24-N6H66+, 32-C9-N6H66+a,n d 32-N8HSs+F, igure 1) has been studied in aqueous solution at room temperature. In all cases a simple photoaquation reaction takes place, with substitution of one CN- ligand by HzO. The quantum yield of the photoaquation reaction (a = 0.30 for the free CO(CN) ~c~om- plex) is not affected by the presence of Et2NHz+b ut decreases when Co(CN):- is associated with polyammonium ions. Specifically, the photoaquation quantum yield drops to 0.15, 0.1 1, and 0.10 when CO(CN)63- is associated with 24-N6H66+3, 2-C9-N6H66+a,n d 32-N8HB8+re, spectively. The reduction of the quantum yield is interpreted by assuming that only a discrete number of CN- are allowed to dissociate in the adducts. This agrees with the formation of adducts of defined molecular structure, in which some of the CN- ligands are bound to the plyammonium receptor and are thus prevented from escaping when the Co-CN bonds are temporarily broken as a consequence of light excitation. These adducts may be considered as complexes of complexes (or supercomplexes) since the ligands coordinated in the first coordination sphere of the metal in their turn coordinate a macrocyclic ligand. The results obtained indicate that it is possible to protect coordination compounds against ligand photodissociation by using appropriate receptors and they are also promising for other applications related to the control of photochemical reactions