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Search Results: 1 - 10 of 611250 matches for " J. M. van Ruitenbeek "
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Conductance quantisation in metallic point contacts
J. M. van Ruitenbeek
Physics , 1999,
Abstract: The electrical transport properties of atomic-scale conductors are reviewed, with an emphasis on the relations of this problem with studies on quantum size effects in metallic clusters. A brief introduction is given of the natural formalism for discussing electron transport in ballistic conductors: the Landauer theory. After introducing the experimental techniques, which are used for studying ballistic point contacts in metals, the experimental observations for the conductance of atomic-scale contacts are presented. In order to obtain a full description in terms of the quantum modes for conductance, several recently developed techniques are reviewed, which go beyond straightforward measurement of the conductance. A brief discussion is given of an unusual atomic geometry for gold contacts, which evolve into a chain of freely suspended atoms. Then shell filling effects in sodium nanowires are discussed in the context of the influence of the conductance modes on the total energy of the system. The chapter ends with an outlook on promising new developments.
Thermopower of atomic-size metallic contacts
B. Ludoph,J. M. van Ruitenbeek
Physics , 1998, DOI: 10.1103/PhysRevB.59.12290
Abstract: The thermopower and conductance of atomic-size metallic contacts have been simultaneously measured using a mechanically controllable break junction. For contacts approaching atomic dimensions, abrupt steps in the thermopower are observed which coincide with jumps in the conductance. The measured thermopower for a large number of atomic-size contacts is randomly distributed around the value for large contacts and can be either positive or negative in sign. However, it is suppressed at the quantum value of the conductance G_0 = 2e^2/h. We derive an expression that describes these results in terms of quantum interference of electrons backscattered in the banks.
Observation of shell effects in nanowires for the noble metals copper, silver and gold
A. I. Mares,J. M. van Ruitenbeek
Physics , 2005, DOI: 10.1103/PhysRevB.72.205402
Abstract: We extend our previous shell effect observation in gold nanowires at room temperature under ultra high vacuum to the other two noble metals: silver and copper. Similar to gold, silver nanowires present two series of exceptionally stable diameters related to electronic and atomic shell filling. This observation is in concordance to what was previously found for alkali metal nanowires. Copper however presents only electronic shell filling. Remarkably we find that shell structure survives under ambient conditions for gold and silver.
Conductance fluctuations as a tool for investigating the quantum modes in atomic size metallic contacts
B. Ludoph,J. M. van Ruitenbeek
Physics , 1999, DOI: 10.1103/PhysRevB.61.2273
Abstract: Recently it has been observed that the conductance fluctuations of atomic size gold contacts are suppressed when the conductance is equal to an integer multiple of the conductance quantum. The fact that these contacts tend to consist exclusively of fully open or closed modes has been argued to be the origin for this suppression. Here, the experiments have been extended to a wide range of metallic elements with different chemical valence and they provide new information about the relation between the mode composition and statistically preferred conductance values observed in conductance histograms.
Quantum suppression of shot noise in atom-size metallic contacts
H. E. van den Brom,J. M. van Ruitenbeek
Physics , 1998, DOI: 10.1103/PhysRevLett.82.1526
Abstract: The transmission of conductance modes in atom-size gold contacts is investigated by simultaneously measuring conductance and shot noise. The results give unambiguous evidence that the current in the smallest gold contacts is mostly carried by nearly fully transmitted modes. In particular, for a single-atom contact the contribution of additional modes is only a few percent. In contrast, the trivalent metal aluminum does not show this property.
Electron-vibration interaction in single-molecule junctions: from contact to tunneling regime
O. Tal,M. Krieger,B. Leerink,J. M. van Ruitenbeek
Physics , 2008, DOI: 10.1103/PhysRevLett.100.196804
Abstract: Point contact spectroscopy on a H2O molecule bridging Pt electrodes reveals a clear crossover between enhancement and reduction of the conductance due to electron-vibration interaction. As single channel models predict such a crossover at transmission probability of t=0.5, we used shot noise measurements to analyze the transmission and observed at least two channels across the junction where the dominant channel has t=0.51+/-0.01 transmission probability at the crossover conductance, which is consistent with the predictions for single-channel models.
High-bias stability of monatomic chains
R. H. M. Smit,C. Untiedt,J. M. van Ruitenbeek
Physics , 2003, DOI: 10.1088/0957-4484/15/7/055
Abstract: For the metals Au, Pt and Ir it is possible to form freely suspended monatomic chains between bulk electrodes. The atomic chains sustain very large current densities, but finally fail at high bias. We investigate the breaking mechanism, that involves current-induced heating of the atomic wires and electromigration forces. We find good agreement of the observations for Au based on models due to Todorov and coworkers. The high-bias breaking of atomic chains for Pt can also be described by the models, although here the parameters have not been obtained independently. In the limit of long chains the breaking voltage decreases inversely proportional to the length.
Effect of bonding of a CO molecule on the conductance of atomic metal wires
M. Kiguchi,D. Djukic,J. M. van Ruitenbeek
Physics , 2006, DOI: 10.1088/0957-4484/18/3/035205
Abstract: We have measured the effect of bonding of a CO molecule on the conductance of Au, Cu, Pt, and Ni atomic contacts at 4.2 K. When CO gas is admitted to the metal nano contacts, a conductance feature appears in the conductance histogram near 0.5 of the quantum unit of conductance, for all metals. For Au, the intensity of this fractional conductance feature can be tuned with the bias voltage, and it disappears at high bias voltage (above $\sim$ 200 mV). The bonding of CO to Au appears to be weakest, and associated with monotomic Au wire formation.
Magneto-orientation and quantum size effect in SP-STM conductance in the presence of a subsurface magnetic cluster
Ye. S. Avotina,Yu. A. Kolesnichenko,J. M. van Ruitenbeek
Physics , 2009, DOI: 10.1103/PhysRevB.80.115333
Abstract: The influence of a single magnetic cluster in a non-magnetic host metal on the spin current $\mathbf{j}^{(s)}$ and the charge current $\mathbf{j}$ in the vicinity of a ferromagnetic STM tip is studied theoretically. Spin-flip processes due to electron interaction with the cluster are taken into account. We show that quantum interference between the partial waves injected from the STM tip and those scattered by the cluster results in the appearance of components perpendicular to the initial polarization of the spin current $\mathbf{j}^{(s)}$, which obtain a strongly inhomogeneous spatial distribution. This interference produces oscillations of the conductance as a function of the distance between the contact and the cluster center. The oscillation amplitude depends on the current polarization. We predict a strong magneto-orientational effect: the conductance oscillations may grow, shrink, or even vanish for rotation of the cluster magnetic moment $\mathbf{\mu}_{\mathrm{eff}}$ by an external magnetic field. These results can be used for the determination of the $ \mathbf{\mu}_{\mathrm{eff}}$ for magnetic clusters below a metal surface.
Theory of oscillations in the STM conductance resulting from subsurface defects (Review Article)
Ye. S. Avotina,Yu. A. Kolesnichenko,J. M. van Ruitenbeek
Physics , 2010, DOI: 10.1063/1.3514417
Abstract: In this review we present recent theoretical results concerning investigations of single subsurface defects by means of a scanning tunneling microscope (STM). These investigations are based on the effect of quantum interference between the electron partial waves that are directly transmitted through the contact and the partial waves scattered by the defect. In particular, we have shown the possibility imaging the defect position below a metal surface by means of STM. Different types of subsurface defects have been discussed: point-like magnetic and non-magnetic defects, magnetic clusters in a nonmagnetic host metal, and non-magnetic defects in a s-wave superconductor. The effect of Fermi surface anisotropy has been analyzed. Also, results of investigations of the effect of a strong magnetic field to the STM conductance of a tunnel point contact in the presence of a single defect has been presented.
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