| 1. |
- Shekhter, Robert I., 1947, et al.
(författare)
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Mechano-electronic and electro-mechanical energy transfer in mesoscopic superconducting weak links
- 2012
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Ingår i: Comptes Rendus Physique. - : Elsevier BV. - 1878-1535 .- 1631-0705. ; 13:5, s. 426-439
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Forskningsöversikt (refereegranskat)abstract
- In this review we discuss how the nano-electro-mechanical properties of a superconducting weak link, formed by a suspended nanowire bridging two superconductors, can strongly affect mesoscopic effects in both the electronic and the mechanical subsystem. In particular we will discuss how quantum coherence and electron–electron (Coulomb) correlations may result in the possibility to resonantly redistribute energy between the electronic and mechanical degrees of freedom, allowing controllable switching between pumping and cooling of the nano-mechanical vibrations of the suspended nanowire. The two regimes of a given current and a given voltage supplied to the nano-electro-mechanical weak link is considered, resulting respectively in the possibility of ground-state cooling or resonant generation of nano-mechanical vibrations for realistic experimental parameters.
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| 2. |
- Shekhter, Robert I., 1947, et al.
(författare)
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Nonequilibrium and quantum coherent phenomena in the electromechanics of suspended nanowires
- 2009
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1090-6517 .- 1063-777X. ; 35:8
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Forskningsöversikt (refereegranskat)abstract
- Strong coupling between electronic and mechanical degrees of freedom is a basic requirement for the operation of any nanoelectromechanical device. In this Review we consider such devices and in particular investigate the properties of small tunnel-junction nanostructures that contain a movable element in the form of a suspended nanowire. In these systems, electrical currents and charge can be concentrated to small spatial volumes resulting in strong coupling between the mechanics and the charge transport. As a result, a variety of mesoscopic phenomena appear, which can be used for the transduction of electrical currents into mechanical operation. Here we will in particular consider nanoelectromechanical dynamics far from equilibrium and the effect of quantum coherence in both the electronic and mechanical degrees of freedom in the context of both normal and superconducting nanostructures.
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| 3. |
- Sonne, Gustav, 1982, et al.
(författare)
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Cooling of a suspended nanowire by an ac Josephson current flow
- 2010
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 104:22
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Tidskriftsartikel (refereegranskat)abstract
- We consider a nanoelectromechanical Josephson junction, where a suspended nanowire serves as a superconducting weak link, and show that an applied dc bias voltage can result in suppression of the flexural vibrations of the wire. This cooling effect is achieved through the transfer of vibronic energy quanta first to voltage-driven Andreev states and then to extended quasiparticle electronic states. Our analysis, which is performed for a nanowire in the form of a metallic carbon nanotube and in the framework of the density matrix formalism, shows that such self-cooling is possible down to the ground state of the flexural vibration mode of the nanowire.
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| 4. |
- Sonne, Gustav, 1982, et al.
(författare)
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Ground-State Cooling of a Suspended Nanowire through Inelastic Macroscopic Quantum Tunneling in a Current-Biased Josephson Junction
- 2011
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Ingår i: Physical Reveiw Letters. - 0031-9007 .- 1079-7114. ; 106:16
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that a suspended nanowire forming a weak link between two superconductors can be cooled to its motional ground state by a supercurrent flow. The predicted cooling mechanism has its origins in magnetic field induced inelastic tunneling of the macroscopic superconducting phase associated with the junction. Furthermore, we show that the voltage drop over the junction is proportional to the average population of the vibrational modes in the stationary regime, a phenomenon which can be used to probe the level of cooling.
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| 5. |
- Sonne, Gustav, 1982, et al.
(författare)
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High-temperature excess current and quantum suppression of electronic backscattering
- 2008
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Ingår i: Europhysics Letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 84
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Tidskriftsartikel (refereegranskat)abstract
- We consider the electronic current through a one-dimensional conductor in the ballistic transport regime and show that the quantum oscillations of a weakly pinned single-scattering target results in a temperature- and bias-voltage independent excess current at large bias voltages. This is a genuine quantum effect on transport that derives from an exponential reduction of electron backscattering in the elastic channel due to quantum delocalisation of the scatterer and from a suppression of low-energy electron backscattering in the inelastic channels caused by the Pauli exclusion principle. We show that both the mass of the target and the frequency of its quantum vibrations can be measured by studying the differential conductance and the excess current. We apply our analysis to the particular case of a weakly pinned C60 molecule encapsulated by a single-wall carbon nanotube and find that the discussed phenomena are experimentally observable.
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| 6. |
- Sonne, Gustav, 1982
(författare)
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Mesoscopic phenomena in the electromechanics of suspended nanowires
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Over the last two decades nanotechnology has been a very active field of scientific research, both from fundamental perspectives as well as for applications in technology and consumer goods. In this thesis, theoretical work on quantum mechanical effects on charge transport in nanoelectromechanical systems is presented. In particular, the effects of electron-vibron interactions in suspended nanowire structures are analysed and discussed. The thesis is structured around the appended scientific publications by the author. Also included is an introductory section where the underlying theory and motivation is presented. This introduction forms the basis on which the subsequent material and appended papers is based. The work presented in the appended papers considers systems comprising suspended oscillating nanowires, primarily in the form of carbon nanotubes. Central to these studies is the interaction between the charge transport and the mechanical motion of the nanowires. For the systems analysed in this thesis, these interactions are mediated through transverse magnetic fields, the effect of which is studied in various system setups. In particular, three topics of mesoscopic phenomena are presented; i) a temperature-independent current deficit due to interference effects between different electronic tunnelling paths over the nanowire-junction, ii) pumping of the mechanical vibrations in a low transparency superconducting junction, and iii) cooling of the mechanical vibrations in both current- and voltage-biased superconducting junctions. The outcome of the presented work is a number of interesting physical predictions for the electromechanics of suspended nanowires. These results are shown to be experimentally observable in systems with high mechanical resonance frequencies and if sufficiently strong electromechanical coupling can be achieved. Once these conditions are fulfilled, the predicted results are of interest both from a fundamental perspective in that they probe the underlying quantum nature of the systems, but also for sensing applications where quantum limited resolution could be experimentally achievable.
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| 7. |
- Sonne, Gustav, 1982
(författare)
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Quantum mechanical effects on charge transport in two mesoscopic systems
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Carbon nanotubes are one of the most promising building blocks for the developing field of nanoelectromechanics. Due to their unique electronic and mechanical properties, these all-carbon systems have been suggested for a range of applications where one wishes to utilse the coupling between mechanical and electronic degrees of freedom on the nanometer length scale. In this thesis two carbon nanotube based systems are studied. the first system under consideration is a carbon pepaod, a caron nanotube encapsulating a single scattering C60 fullerene. By considering the scattering molecule to be weakly pinned along the axis of the tube we study the influence of its vibrational motion on the ballistic electron transport through the tube. This analysis shows that in the weak scattering limit the back-flow current is reduced as compared to the case when the fullerene is static. This effect is attributed to a renormalisation in the elastic backscattering channel due to smearing out of the fullerenes position, as well as a suppression of the inelastic backscattering channels due to the Pauli principle which restricts the number of final energy quantum states of the oscillator. The main result of this analysis is that we predict a temperature and bias voltage independent excess current which should be readily observable for realistic experimental parameters. Also, the differential and linear conductance is studied and is shown to exhibit clear signatures of measurable quantum effects in this system. The second system studied comprises a suspended carbon nanotube coupled to two superconducting leads in a transverse magnetic field. By voltage biasing the two leads an ac current is induced along the wire which, due to the coupling to the magnetic field, drives the wire into a n oscillatory state. This in turn induces an electromotive force along the wire which modulates the phase-difference over the leads, resulting in a system of coupled equations for the vibrational amplitude of the wire, which, in the low temperature limit, is shown to give rise to novel resonance phenomena. An analytic analysis of the subsequent oscillatory motion is presented which predicts the system to exhibit a region of bistability in the vibrational amplitude and measurable dc current, which is also confirmed by numerical simulations.
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| 8. |
- Sonne, Gustav, 1982, et al.
(författare)
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Superconducting pumping of nanomechanical vibrations
- 2008
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Ingår i: Physical Review B. - 1098-0121. ; 78, s. 144501-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that a supercurrent can pump energy from a battery that provides a voltage bias into nanomechanical vibrations. Using a device containing a nanowire Josephson weak link as an example we show that a nonlinear coupling between the supercurrent and a static external magnetic field leads to a Lorentz force that excites bending vibrations of the wire at resonance conditions. We also demonstrate the possibility to achieve more than one regime of stationary nonlinear vibrations and how to detect them via the associated dc Josephson currents and we discuss possible applications of such a multistable nanoelectromechanical dynamics.
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| 9. |
- Sonne, Gustav, 1982
(författare)
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Temperature-independent current deficit due to induced quantum nanowire vibrations
- 2009
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- We consider electronic transport through a suspended voltage-biased nanowire subject to an external magnetic field. In this paper, we show that the transverse magnetic field, which acts to induce coupling between the tunneling current and the vibrational modes of the wire, controls the current–voltage characteristics of the system in novel ways. In particular, we derive the quantum master equation for the reduced density matrix describing the nanowire vibrations. From this we find a temperature- and bias voltage-independent current deficit in the limit of high bias voltage since the current through the device is lower than its value at zero magnetic field. We also find that the corrections to the current from the back-action of the vibrating wire decay exponentially in the limit of high voltage. Furthermore, it is shown that the expression for the temperature- and bias voltage-independent current deficit holds even if the nanowire vibrational modes have been driven out of thermal equilibrium.
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| 10. |
- Sonne, Gustav, 1982, et al.
(författare)
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Voltage-driven superconducting weak link as a refrigerator for cooling of nanomechanical vibrations
- 2010
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1090-6517 .- 1063-777X. ; 36:10
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Tidskriftsartikel (refereegranskat)abstract
- We consider a new type of cooling mechanism for a suspended nanowire acting as a weak link between two superconductive electrodes. By applying a bias voltage over the system, we show that the system can be viewed as a refrigerator for the nanomechanical vibrations, where energy is continuously transferred from the vibrational degrees of freedom to the extended quasiparticle states in the leads through the periodic modulation of the inter-Andreev level separation. The necessary coupling between the electronic and mechanical degrees of freedom responsible for this energy-transfer can be achieved both with an external magnetic or electrical field, and is shown to lead to an effective cooling of the vibrating nanowire. Using realistic parameters for a suspended nanowire in the form of a metallic carbon nanotube we analyze the evolution of the density matrix and demonstrate the possibility to cool the system down to a stationary vibron population of ~0.1. Furthermore, it is shown that the stationary occupancy of the vibrational modes of the nanowire can be directly probed from the dc current responsible for carrying away the absorbed energy from the vibrating nanowire.
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