An improved 2.5 GHz electron pump: single-electron transport through shallow-etched point contacts driven by surface acoustic waves

We present an experimental study of a 2.5 GHz electron pump based on the quantized acoustoelectric current driven by surface acoustic waves (SAWs) through a shallow-etched point contact in a GaAs/AlGaAs heterostructure. At low temperatures and with an additional counter-propagating SAW beam, up to n = 20 current plateaus at I=nef could be resolved, where n is an integer, e the electron charge, and f the SAW frequency. In the best case the accuracy of the first plateau at 0.40 nA was estimated to be dI/I = +/- 25 ppm over 0.25 mV in gate voltage, which is better than previous results.Comment: 11 pages, 4 figure

Different quantization mechanisms in single-electron pumps driven by surface acoustic waves

We have studied the acoustoelectric current in single-electron pumps driven by surface acoustic waves. We have found that in certain parameter ranges two different sets of quantized steps dominate the acoustoelectric current versus gate-voltage characteristics. In some cases, both types of quantized steps appear simultaneously though at different current values, as if they were superposed on each other. This could indicate two independent quantization mechanisms for the acoustoelectric current.Comment: 6 pages, 3 figure

The Influence of Electro-Mechanical Effects on Resonant Electron Tunneling Through Small Carbon Nano-Peapods

The influence of a fullerene molecule trapped inside a single-wall carbon nanotube on resonant electron transport at low temperatures and strong polaronic coupling is theoretically discussed. Strong peak to peak fluctuations and anomalous temperature behavior of conductance amplitudes are predicted and investigated. The influence of the chiral properties of carbon nanotubes on transport is also studied.Comment: 17 pages, 3 figures. Replaced with published version. Important changes. Open access: http://stacks.iop.org/1367-2630/10/04304

Single-electron transport driven by surface acoustic waves: moving quantum dots versus short barriers

We have investigated the response of the acoustoelectric current driven by a surface-acoustic wave through a quantum point contact in the closed-channel regime. Under proper conditions, the current develops plateaus at integer multiples of ef when the frequency f of the surface-acoustic wave or the gate voltage Vg of the point contact is varied. A pronounced 1.1 MHz beat period of the current indicates that the interference of the surface-acoustic wave with reflected waves matters. This is supported by the results obtained after a second independent beam of surface-acoustic wave was added, traveling in opposite direction. We have found that two sub-intervals can be distinguished within the 1.1 MHz modulation period, where two different sets of plateaus dominate the acoustoelectric-current versus gate-voltage characteristics. In some cases, both types of quantized steps appeared simultaneously, though at different current values, as if they were superposed on each other. Their presence could result from two independent quantization mechanisms for the acoustoelectric current. We point out that short potential barriers determining the properties of our nominally long constrictions could lead to an additional quantization mechanism, independent from those described in the standard model of 'moving quantum dots'.Comment: 25 pages, 12 figures, to be published in a special issue of J. Low Temp. Phys. in honour of Prof. F. Pobel

Single-qubit gates and measurements in the surface acoustic wave quantum computer

In the surface acoustic wave quantum computer, the spin state of an electron trapped in a moving quantum dot comprises the physical qubit of the scheme. Via detailed analytic and numerical modeling of the qubit dynamics, we discuss the effect of excitations into higher-energy orbital states of the quantum dot that occur when the qubits pass through magnetic fields. We describe how single-qubit quantum operations, such as single-qubit rotations and single-qubit measurements, can be performed using only localized static magnetic fields. The models provide useful parameter regimes to be explored experimentally when the requirements on semiconductor gate fabrication and the nanomagnetics technology are met in the future.Comment: 13 pages, 10 figures, submitted to Phys. Rev.

Nanoelectromechanical coupling in fullerene peapods probed via resonant electrical transport experiments

Fullerene peapods, that is carbon nanotubes encapsulating fullerene molecules, can offer enhanced functionality with respect to empty nanotubes. However, the present incomplete understanding of how a nanotube is affected by entrapped fullerenes is an obstacle for peapods to reach their full potential in nanoscale electronic applications. Here, we investigate the effect of C60 fullerenes on electron transport via peapod quantum dots. Compared to empty nanotubes, we find an abnormal temperature dependence of Coulomb blockade oscillations, indicating the presence of a nanoelectromechanical coupling between electronic states of the nanotube and mechanical vibrations of the fullerenes. This provides a method to detect the C60 presence and to probe the interplay between electrical and mechanical excitations in peapods, which thus emerge as a new class of nanoelectromechanical systems.Comment: 7 pages, 3 figures. Published in Nature Communications. Free online access to the published version until Sept 30th, 2010, see http://www.nature.com/ncomms/journal/v1/n4/abs/ncomms1034.htm

Sub-Kelvin transport spectroscopy of fullerene peapod quantum dots

International audienceThe authors have studied electrical transport properties of individual C60 fullerene peapods, i.e., single-wall carbon nanotubes encapsulating C60 molecules. Their measurements indicated power lawlike temperature dependencies of linear conductance similar to those for empty nanotubes. At temperatures below 30K, peapod devices behaved as highly regular individual quantum dots showing regular Coulomb blockade oscillations. Signatures of Kondo physics appeared at the lowest measurement temperature of 315mK

Molecular magnetic materials

The „molecular” term appears more and more often in the materials chemistry. The Nobel Prize in 2016 was awarded to Jean-Pierre Sauvage, Sir J. Fraser Stoddart and Bernard R. Feringa „for the design and synthesis of molecular machines”. Magnetism in molecular scale, also known as molecular nanomagnetism, has been developing intensively since the second half of the last century. This branch of science involves the magnetic properties of coordination compounds of d- and f-electron metals. The paper presents results of the magnetic studies of molecular magnets of copper(II) and dysprosium(III), which have been pursuing in two doctoral thesis. The compounds form trinuclear and triangular molecules. The spin frustration phenomenon observed in the triangular relationship of copper(II) has been described. Since dysprosium(III) ion is characterized by a large magnetic anisotropy, the triangular, trinuclear coordination compound of dysprosium(III) of the formula [Dy3L5HLCl4]∙HL (where HL = 2-methoxyethanol) presents the characteristic properties of molecular magnets (SMMs) behavior. Two values of the energy barier were determined as Ueff/kB = 84,6 K and 31,2 K with the corresponding relaxation times τ0 = 1,82·10-6 s and 5,19·10-5 s. The data are probably attributed to different geometry of the coupled dysprosium ions

New members in the [Mn10] supertetrahedron family

Two manganese complexes, [MnII4MnIII6Cl4(CH3OCH2CH2O)12 O4][MnII3TiIVCl6(CH3OCH2CH2O)6] (1) and [MnII4MnIII6Cl4(CH3OCH2CH2O)12O4] [Mn4II Cl10(CH3OCH2CH2OH)4]∙0.5CH3OCH2CH2OH, (2) have been obtained and characterized by single-crystal X-ray diffraction. Both structures consist of the decametallic dicationic [MnII4MnIII6Cl4(CH3OCH2CH2O)12O4]2 + core constructed by four vertex-sharing [MnIII3MnIIO]9 + tetrahedra. Also, these compounds contain the different tetrametallic dianions: [MnII3TiIVCl6(CH3OCH2CH2O)6]2 − (in complex 1) and [Mn4IICl10(CH3OCH2CH2OH)4]2 − (in complex 2). Magnetic dc and ac susceptibility measurements for compound (1) show that the dicationic decanuclear magnetic cluster possesses an S = 12 ± 1 spin ground-state