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Register a new userNarrow-line single-molecule transducer between electronic circuits and surface plasmons
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A molecular wire containing an emitting molecular center is controllably suspended between the plasmonic electrodes of a cryogenic scanning tunneling microscope. Passing current through this circuit generates an ultra narrow-line emission at an energy of ? 1.5 eV which is assigned to the fluorescence of the molecular center. Control over the linewidth is obtained by progressively detaching the emitting unit from the surface. The recorded spectra also reveal several vibronic peaks of low intensities that can be viewed as a fingerprint of the emitter. Surface-plasmon localized at the tip-sample interface are shown to play a major role on both excitation and emission of the molecular excitons.
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In this work we study theoretically the coupling of single molecule magnets (SMMs) to a variety of quantum circuits, including microwave resonators with and without constrictions and flux qubits. The main results of this study is that it is possible to achieve strong and ultrastrong coupling regimes between SMM crystals and the superconducting circuit, with strong hints that such a coupling could also be reached for individual molecules close to constrictions. Building on the resulting coupling strengths and the typical coherence times of these molecules (of the order of microseconds), we conclude that SMMs can be used for coherent storage and manipulation of quantum information, either in the context of quantum computing or in quantum simulations. Throughout the work we also discuss in detail the family of molecules that are most suitable for such operations, based not only on the coupling strength, but also on the typical energy gaps and the simplicity with which they can be tuned and oriented. Finally, we also discuss practical advantages of SMMs, such as the possibility to fabricate the SMMs ensembles on the chip through the deposition of small droplets.
In plasmonic chirality, the phenomenon of circular dichroism for achiral nanoparitcles caused by Coulomb interaction between metal nanoparticles (NPs) and chiral molecules have been studied. At the same time, under the resonance condition, the dye molecules and metal NPs will produce huge Rabi splitting due to strong coupling. If the chiral molecules are at the resonance of the plasmon, what will happen for the strong interaction between the plasmon and molecules with chirality introduced? In this paper, we investigate a spherical core-shell model and analyze its spectral phenomena under the excitation of circularly polarized light (CPL). Based on Coulomb interaction between NPs and chiral molecules, we will show how the various factors affect the strong coupling. We have obtained three mechanisms for the interaction between plasmons and chiral molecules: strong coupling (Rabi splitting up to 243mev), enhanced absorption and induced transparency. The interaction between CPL and chiral molecules with the opposite chirality to CPL is stronger than that of the same chirality, and the line width of the two peaks is closer than that of the same chirality, which shows that for the Rabi splitting with chirality, there are deeper mechanisms for the interaction. This result will be helpful for further research on the interaction between plasmon and molecules with chirality.
We present a general analytical formula and an ab initio study of quantum interference in multi-branch molecules. Ab initio calculations are used to investigate quantum interference in a benzene-1,2-dithiolate (BDT) molecule sandwiched between gold electrodes and through oligoynes of various lengths. We show that when a point charge is located in the plane of a BDT molecule and its position varied, the electrical conductance exhibits a clear interference effect, whereas when the charge approaches a BDT molecule along a line normal to the plane of the molecule and passing through the centre of the phenyl ring, interference effects are negligible. In the case of olygoynes, quantum interference leads to the appearance of a critical energy $E_c$, at which the electron transmission coefficient $T(E)$ of chains with even or odd numbers of atoms is independent of length. To illustrate the underlying physics, we derive a general analytical formula for electron transport through multi-branch structures and demonstrate the versatility of the formula by comparing it with the above ab-initio simulations. We also employ the analytical formula to investigate the current inside the molecule and demonstrate that large counter currents can occur within a ring-like molecule such as BDT, when the point charge is located in the plane of the molecule. The formula can be used to describe quantum interference and Fano resonances in structures with branches containing arbitrary elastic scattering regions connected to nodal sites.
A comprehensive review is presented of single molecule junction conductance measurements across families of molecules measured while breaking a gold point contact in a solution of molecules with amine end groups. A theoretical framework unifies the picture for the amine-gold link bonding and the tunnel coupling through the junction using Density Functional Theory based calculations. The reproducible electrical characteristics and utility for many molecules is shown to result from the selective binding between the gold electrodes and amine link groups through a donor-acceptor bond to undercoordinated gold atoms. While the bond energy is modest, the maximum force sustained by the junction is comparable to, but less than, that required to break gold point contacts. The calculated tunnel coupling provides conductance trends for all 41 molecule measurements presented here, as well as insight into the variability of conductance due to the conformational changes within molecules with torsional degrees of freedom. The calculated trends agree to within a factor of two of the measured values for conductance ranging from 10-7 G0 to 10-2 G0, where G0 is the quantum of conductance (2e2/h).
The single molecule magnet (SMM) bis(phthalocyaninato)terbium (III) (TbPc$_2$) has attracted steady research attention as an exemplar system for realizing molecule-based spin electronics. In this paper, we report on the spontaneous formation of Tb$_2$Pc$_3$ species from TbPc$_2$ precursors via sublimation in ultrahigh vacuum (UHV) onto an Ag(111) surface. The molecules on the surface are inspected using combined scanning tunneling (STM) and non-contact atomic force microscopies (nc-AFM) at 5 Kelvin. Submolecular resolution and height dependent measurements supported by density functional theory (DFT) calculations unambiguously show the presence of both TbPc$_2$ and Tb$_2$Pc$_3$ species. The synthesis of Tb$_2$Pc$_3$ species under UHV conditions is independently confirmed by chemical analysis. The high-resolution AFM imaging allows us to register the orientation of the topmost Pc ligand in both Tb$_2$Pc$_3$ and TbPc$_2$ relative to the underlying Ag(111) surface. Measurements of the electronic structure reveal the selective appearance of a Kondo signature with temperature $sim$ 30K in the Tb$_2$Pc$_3$ species, localized to the Pc ligand lobes. We attribute the presence of the Kondo resonance on select Tb$_2$Pc$_3$ molecules to the orientation of internal molecular ligands. High-resolution AFM imaging identifies geometric distortions between Tb$_2$Pc$_3$ molecules with and without the Kondo effect, the result of the complex interplay between structural and electronic differences.
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