A Molecular Platinum Cluster Junction: A Single-Molecule Switch

We present a theoretical study of electron transport through single-molecule junctions incorporating a Pt₆ metal cluster bound within an organic framework. The insertion of this molecule between a pair of electrodes leads to a fully atomically engineered nanometallic device with high conductance at the Fermi level and two sequential high on/off switching states. The origin of this property can be traced back to the existence of a degenerate HOMO consisting of two asymmetric orbitals with energies close to the Fermi level of the metal leads. The degeneracy is broken when the molecule is contacted to the leads, giving rise to two resonances that become pinned to the Fermi level and display destructive interference

Exploring the Limits of Super-Planckian Far-Field Radiative Heat Transfer Using 2D Materials

Very recently it has been predicted that the far-field radiative heat transfer between two macroscopic systems can largely overcome the limit set by Planck’s law if one of their dimensions becomes much smaller than the thermal wavelength (λ_Th ≈ 10 μm at room temperature). To explore the ultimate limit of the far-field violation of Planck’s law, here we present a theoretical study of the radiative heat transfer between two-dimensional (2D) materials. We show that the far-field thermal radiation exchanged by two coplanar systems with a one-atom-thick geometrical cross section can be more than 7 orders of magnitude larger than the theoretical limit set by Planck’s law for blackbodies and can be comparable to the heat transfer of two parallel sheets at the same distance. In particular, we illustrate this phenomenon with different materials such as graphene, where the radiation can also be tuned by a external gate, and single-layer black phosphorus. In both cases the far-field radiative heat transfer is dominated by TE-polarized guiding modes, and surface plasmons play no role. Our predictions provide a new insight into the thermal radiation exchange mechanisms between 2D materials

Plasmon-Induced Conductance Enhancement in Single-Molecule Junctions

The effect of surface plasmons on the conductance of single-molecule junctions is studied using a squeezable break junction setup. We show that the conductance of 2,7-diaminofluorene single-molecule junctions can be enhanced upon laser irradiation. Our experimental approach enables us to show that this enhancement is due to the plasmon-induced oscillating field within the nanoscale metal gap of the junctions. The effective plasmon field enhancement within the gap is calculated to be ∼1000. The experimental procedure presented in this work, which enables one to explore the coupling between plasmons and molecular excitations via transport measurements, could potentially become a valuable tool in the field of plexcitonics

Bioengineering a Single-Protein Junction

Bioelectronics moves toward designing nanoscale electronic platforms that allow <i>in vivo</i> determinations. Such devices require interfacing complex biomolecular moieties as the sensing units to an electronic platform for signal transduction. Inevitably, a systematic design goes through a bottom-up understanding of the structurally related electrical signatures of the biomolecular circuit, which will ultimately lead us to tailor its electrical properties. Toward this aim, we show here the first example of bioengineered charge transport in a single-protein electrical contact. The results reveal that a single point-site mutation at the docking hydrophobic patch of a Cu-azurin causes minor structural distortion of the protein blue Cu site and a dramatic change in the charge transport regime of the single-protein contact, which goes from the classical Cu-mediated two-step transport in this system to a direct coherent tunneling. Our extensive spectroscopic studies and molecular-dynamics simulations show that the proteins’ folding structures are preserved in the single-protein junction. The DFT-computed frontier orbital of the relevant protein segments suggests that the Cu center participation in each protein variant accounts for the different observed charge transport behavior. This work is a direct evidence of charge transport control in a protein backbone through external mutagenesis and a unique nanoscale platform to study structurally related biological electron transfer

Flux-Tunable Josephson Diode Effect in a Hybrid Four-Terminal Josephson Junction

We investigate the direction-dependent switching current in a flux-tunable four-terminal Josephson junction defined in an InAs/Al two-dimensional heterostructure. The device exhibits the Josephson diode effect with switching currents that depend on the sign of the bias current. The superconducting diode efficiency, reaching a maximum of |η| ≈ 34%, is widely tunableboth in amplitude and signas a function of magnetic fluxes and gate voltages. Our observations are supported by a circuit model of three parallel Josephson junctions with nonsinusoidal current–phase relation. With respect to conventional Josephson interferometers, phase-tunable multiterminal Josephson junctions enable large diode efficiencies in structurally symmetric devices, where local magnetic fluxes generated on the chip break both time-reversal and spatial symmetries. Our work presents an approach for developing Josephson diodes with wide-range tunability that do not rely on exotic materials