Richard Korytár

Atomically Wired Molecular Junctions: Connecting a Single Organic Molecule by Chains of Metal Atoms

Using a break junction technique, we find a clear signature for the formation of conducting hybrid junctions composed of a single organic molecule (benzene, naphthalene, or anthracene) connected to chains of platinum atoms. The hybrid junctions exhibit metallic-like conductance (~0.1-1G0), which is rather insensitive to further elongation by additional atoms. At low bias voltage the hybrid junctions can be elongated significantly beyond the length of the bare atomic chains. Ab initio calculations reveal that benzene based hybrid junctions have a significant binding energy and high structural flexibility that may contribute to the survival of the hybrid junction during the elongation process. The fabrication of hybrid junctions opens the way for combining the different properties of atomic chains and organic molecules to realize a new class of atomic scale interfaces.

Impact of Electrode Density of States on Transport through Pyridine-Linked Single Molecule Junctions

We study the impact of electrode band structure on transport through single-molecule junctions by measuring the conductance of pyridine-based molecules using Ag and Au electrodes. Our experiments are carried out using the scanning tunneling microscope based break-junction technique and are supported by density functional theory based calculations. We find from both experiments and calculations that the coupling of the dominant transport orbital to the metal is stronger for Au-based junctions when compared with Ag-based junctions. We attribute this difference to relativistic effects, which result in an enhanced density of d-states at the Fermi energy for Au compared with Ag. We further show that the alignment of the conducting orbital relative to the Fermi level does not follow the work function difference between two metals and is different for conjugated and saturated systems. We thus demonstrate that the details of the molecular level alignment and electronic coupling in metal-organic interfaces do not follow simple rules but are rather the consequence of subtle local interactions.

Conductance saturation in a series of highly transmitting molecular junctions

Revealing the mechanisms of electronic transport through metal-molecule interfaces is of central importance for a variety of molecule-based devices. A key method for understanding these mechanisms is based on the study of conductance versus molecule length in molecular junctions. However, previous works focused on transport governed either by coherent tunnelling or hopping, both at low conductance. Here, we study the upper limit of conductance across metal-molecule-metal interfaces. Using highly conducting single-molecule junctions based on oligoacenes with increasing length, we find that the conductance saturates at an upper limit where it is independent of molecule length. With the aid of two prototype systems, in which the molecules are contacted by either Ag or Pt electrodes, we find two different possible origins for conductance saturation. The results are explained by an intuitive model, backed by ab initio calculations. Our findings shed light on the mechanisms that constrain the conductance of metal-molecule interfaces at the high-transmission limit.

Incommensurate quantum-size oscillations in acene-based molecular wires—Effects of quantum fluctuations

Molecular wires of the acene-family can be viewed as a physical realization of a two-rung ladder Hamiltonian. For acene-ladders, closed-shell ab initio calculations and elementary zone-folding arguments predict incommensurate gap oscillations as a function of the number of repetitive ring units, NR, exhibiting a period of about ten rings. Results employing open-shell calculations and a mean-field treatment of interactions suggest anti-ferromagnetic correlations that could potentially open a large gap and wash out the gap oscillations. Within the framework of a Hubbard model with repulsive on-site interaction, U, we employ a Hartree-Fock analysis and the density matrix renormalization group to investigate the interplay of gap oscillations and interactions. We confirm the persistence of incommensurate oscillations in acene-type ladder systems for a significant fraction of parameter space spanned by U and NR.

Kondo effect in binuclear metal-organic complexes with weakly interacting spins

We report a combined experimental and theoretical study of the Kondo effect in a series of binuclear metal-organic complexes of the form

Probing Majorana modes in the tunneling spectra of a resonant level.

[{(\mathrm{Me}(\mathrm{hfacac})}_{2}{)}_{2}(\mathrm{bpym})]{}^{0}

Silver Makes Better Electrical Contacts to Thiol‐Terminated Silanes than Gold

, with Me = nickel (II), manganese (II), zinc (II); hfacac = hexafluoroacetylacetonate, and bpym = bipyrimidine, adsorbed on Cu(100) surface. While Kondo features did not appear in the scanning tunneling spectroscopy spectra of nonmagnetic

Electron-Vibration Interaction in the Presence of a Switchable Kondo Resonance Realized in a Molecular Junction

{\mathrm{Zn}}_{2}

Signature of the Dirac cone in the properties of linear oligoacenes

, a zero bias resonance was resolved in magnetic

Spin locking at the apex of nano-scale platinum tips

{\mathrm{Mn}}_{2}