Conductance

About: Conductance is a research topic. Over the lifetime, 8088 publications have been published within this topic receiving 235961 citations.

Non-exponential Length Dependence of Conductance in Iodide-Terminated Oligothiophene Single-Molecule Tunneling Junctions.

Abstract: An exponential decrease of molecular conductance with length has been observed in most molecular systems reported to date, and has been taken as a signature of non-resonant tunneling as the conduction mechanism. Surprisingly, the conductance of iodide-terminated oligothiophene molecules presented herein does not follow the simple exponential length dependence. The lack of temperature dependence in the conductance indicates that tunneling still dominates the conduction mechanism in the molecules. Transition voltage spectroscopy shows that the tunneling barrier of the oligothiophene decreases with length, but the decrease is insufficient to explain the non-exponential length dependence. X-ray photoelectron spectroscopy, stretching length measurement, and theoretical calculations show that the non-exponential length dependence is due to a transition in the binding geometry of the molecule to the electrodes in the molecular junctions as the length increases.

Impact of molecular symmetry on single-molecule conductance.

Abstract: We have measured the single-molecule conductance of a family of bithiophene derivatives terminated with methyl sulfide gold-binding linkers using a scanning tunneling microscope based break-junction technique. We find a broad distribution in the single-molecule conductance of bithiophene compared with that of a methyl sulfide terminated biphenyl. Using a combination of experiments and calculations, we show that this increased breadth in the conductance distribution is explained by the difference in 5-fold symmetry of thiophene rings as compared to the 6-fold symmetry of benzene rings. The reduced symmetry of thiophene rings results in a restriction on the torsion angle space available to these molecules when bound between two metal electrodes in a junction, causing each molecular junction to sample a different set of conformers in the conductance measurements. In contrast, the rotations of biphenyl are essentially unimpeded by junction binding, allowing each molecular junction to sample similar conformers...

Theory of tunneling conductance for normal metal/insulator/triplet superconductor junctions

Abstract: Tunneling conductance spectra of normal metal/insulator/triplet superconductor junctions are investigated theoretically. As triplet paring states we select several types of symmetries that are promising candidates for the superconducting states in UPt$_{3}$ and in Sr$_{2}$RuO$_{4}$. The calculated conductance spectra are sensitive to the orientation of the junction which reflects the anisotropy of the pairing states. They show either zero-bias conductance peaks or gap-like structures depending on the orientation of the junctions. The existence of a residual density of states, peculiar to nonunitary states, is shown to have a significant influence on the properties of the conductance spectra. Present results serve as a guidefor the experimental determination of the symmetry of the pair potentials in UPt$_{3}$ and Sr$_{2}$RuO$_{4}$.

Unified model for conductance through DNA with the Landauer-Büttiker formalism

Abstract: In this work, we model the zero-bias conductance for the four different DNA strands that were used in conductance measurement experiment [A. K. Mahapatro, K. J. Jeong, G. U. Lee, and D. B. Janes, Nanotechnology 18, 195202 (2007)]. Our approach consists of three elements: (i) ab initio calculations of DNA, (ii) Green's function approach for transport calculations, and (iii) the use of two parameters to determine the decoherence rates. We first study the role of the backbone. We find that the backbone can alter the coherent transmission significantly at some energy points by interacting with the bases, though the overall shape of the transmission stays similar for the two cases. More importantly, we find that the coherent electrical conductance is tremendously smaller than what the experiments measure. We consider DNA strands under a variety of different experimental conditions and show that even in the most ideal cases, the calculated coherent conductance is much smaller than the experimental conductance. To understand the reasons for this, we carefully look at the effect of decoherence. By including decoherence, we show that our model can rationalize the measured conductance of the four strands, both qualitatively and quantitatively. We find that the effect of decoherence on $G:C$ base pairs is crucial in getting agreement with the experiments. However, the decoherence on $G:C$ base pairs alone does not explain the experimental conductance in strands containing a number of $A:T$ base pairs. Including decoherence on $A:T$ base pairs is also essential. By fitting the experimental trends and magnitudes in the conductance of the four different DNA molecules, we estimate for the first time that the deocherence rate is 6 meV for $G:C$ and 1.5 meV for $A:T$ base pairs.

Universal conductance distributions in the crossover between diffusive and localization regimes.

Abstract: The full distribution of the conductance P(G) in quasi-one-dimensional wires with rough surfaces is analyzed from the diffusive to the localization regime. In the crossover region, where the statistics is dominated by only one or two eigenchannels, the numerically obtained P(G) is found to be independent of the details of the system with the average conductance as the only scaling parameter. For < or =2e(2)/h, the shape of P(G) remarkably agrees with those predicted by random matrix theory for two fluctuating transmission eigenchannels.