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Quantum size effects in molecular wires and Kondo chains

Friday, September 29, 2017 - 12:00
Place: 
Donostia International Physics Center
Who: 
Richard Korytár, Charles University, Prague
Source Name: 
DIPC

In conventional electronics, the conductance of a wire decreases with length according to Ohm's law. In molecular electronics, quantum effects lead to a richer phenomenology. Oligoacenes are organic molecules which consist of (linearly) fused benzene rings. Recently, Yelin and coworkers studied conductance of oligoacenes directly coupled to Ag leads and found increase of conductance with molecular length.

I will show that electronic transport through oligoacenes is governed by a quantum size effect which controls the alignment and width of the lowest unoccupied molecular orbital. These ideas will be
supported by first-principles transport calculations using density-functional theory.

Linear oligoacenes are one of the simplest realizations of zig-zag terminated graphene nano-ribbons. In the long-wire limit, I will demonstrate that the optical gap as a function of the molecular length shows surprising oscillations with period of approx. 11 rings.

In the second part I focus on systems where the conductance is strongly enhanced by spin fluctuations known as Kondo effect.
I show that Kondo effect can be observed in differential conductance of copper phthalocyanine, a spinfull molecule, when coupled to silver electrodes.
My theoretical result establish the connection of the inelastic signal to the vibrational excitation (breathing mode) of the molecule.

If we assemble chains of atomic-scale magnetic impurities on a metallic surface, we can observe the onset of emergent phases of matter, such as heavy fermions.
In the last part, I will focus on spectroscopic features of Kondo chains, unveiling long-range hybridization between spins mediated by the substrate.

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