| 1. |
- Croy, Alexander, 1981, et al.
(författare)
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Correlation-strength-driven Anderson metal-insulator transition
- 2012
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 85:20
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of driving an Anderson metal-insulator transition in the presence of scale-free disorder by changing the correlation exponent is numerically investigated. We calculate the localization length for quasi-one-dimensional systems at fixed energy and fixed disorder strength using a standard transfer matrix method. From a finite-size scaling analysis we extract the critical correlation exponent and the critical exponent characterizing the phase transition.
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| 2. |
- Croy, Alexander, 1981, et al.
(författare)
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Dynamics of a nanoscale rotor driven by single-electron tunneling
- 2012
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Ingår i: Europhysics Letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 98:6
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Tidskriftsartikel (refereegranskat)abstract
- We investigate theoretically the dynamics and the charge transport properties of a rod-shaped nanoscale rotor, which is driven by a similar mechanism as the nanomechanical single-electron transistor (NEMSET). We show that a static electric potential gradient can lead to self-excitation of oscillatory or continuous rotational motion. We identify the relevant parameters of the device and study the dependence of the dynamics on these parameters. We discuss how the dynamics are related to the measured current through the device. Notably, in the oscillatory regime we find a negative differential conductance. The current-voltage characteristics can be used to infer details of the surrounding environment which is responsible for damping.
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| 3. |
- Croy, Alexander, 1981, et al.
(författare)
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Nonadiabatic electron pumping through interacting quantum dots
- 2012
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 85:3
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Tidskriftsartikel (refereegranskat)abstract
- We study nonadiabatic charge pumping through single-level quantum dots taking into account Coulomb interactions. We show how a truncated set of equations of motion can be propagated in time by means of an auxiliary-mode expansion. This formalism is capable of treating time-dependent electronic transport for arbitrary driving parameters. We verify that the proposed method describes very precisely the well-known limit of adiabatic pumping through quantum dots without Coulomb interactions. As an example we discuss pumping driven by short voltage pulses for various interaction strengths. Such finite pulses are particularly suited to investigation of transient nonadiabatic effects, which may also be important for periodic drivings, where they are much more difficult to reveal.
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| 4. |
- Croy, Alexander, 1981, et al.
(författare)
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Nonadiabatic rectification and current reversal in electron pumps
- 2012
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 86:3
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Tidskriftsartikel (refereegranskat)abstract
- Pumping of electrons through nanoscale devices is one of the fascinating achievements in the field of nanoscience with a wide range of applications. To optimize the performance of pumps, operating them at high frequencies is mandatory. We consider the influence of fast periodic driving on the average charge transferred through a quantum dot. We show that it is possible to reverse the average current by sweeping the driving frequency only. In connection with this, we observe a rectification of the average current for high frequencies. Since both effects are very robust, as corroborated by analytical results for harmonic driving, they offer a new way of controlling electron pumps.
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| 5. |
- Croy, Alexander, 1981, et al.
(författare)
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Nonlinear damping in graphene resonators
- 2012
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 86:23, s. Article Number: 235435-
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Tidskriftsartikel (refereegranskat)abstract
- Based on a continuum mechanical model for single-layer graphene, we propose and analyze a microscopic mechanism for dissipation in nanoelectromechanical graphene resonators. We find that coupling between flexural modes and in-plane phonons leads to linear and nonlinear damping of out-of-plane vibrations. By tuning external parameters such as bias and ac voltages, one can cross over from a linear-to a nonlinear-damping dominated regime. We discuss the behavior of the effective quality factor in this context. DOI: 10.1103/PhysRevB.86.235435
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| 6. |
- Eriksson, Martin, 1989, et al.
(författare)
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Frequency tuning, nonlinearities and mode coupling in circular mechanical graphene resonators
- 2013
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Ingår i: Nanotechnology. - : IOP Publishing. - 1361-6528 .- 0957-4484. ; 24:39, s. srt. no. 395702-
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Tidskriftsartikel (refereegranskat)abstract
- We study circular nanomechanical graphene resonators by means of continuum elasticity theory, treating them as membranes. We derive dynamic equations for the flexural mode amplitudes. Due to the geometrical nonlinearity the mode dynamics can be modeled by coupled Duffing equations. By solving the Airy stress problem we obtain analytic expressions for the eigenfrequencies and nonlinear coefficients as functions of the radius, suspension height, initial tension, back-gate voltage and elastic constants, which we compare with finite element simulations. Using perturbation theory, we show that it is necessary to include the effects of the non-uniform stress distribution for finite deflections. This correctly reproduces the spectrum and frequency tuning of the resonator, including frequency crossings.
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| 7. |
- Midtvedt, Daniel, 1988, et al.
(författare)
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Fermi-Pasta-Ulam Physics with Nanomechanical Graphene Resonators: Intrinsic Relaxation and Thermalization from Flexural Mode Coupling
- 2014
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 112:14
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Tidskriftsartikel (refereegranskat)abstract
- Thermalization in nonlinear systems is a central concept in statistical mechanics and has been extensively studied theoretically since the seminal work of Fermi, Pasta, and Ulam. Using molecular dynamics and continuum modeling of a ring-down setup, we show that thermalization due to nonlinear mode coupling intrinsically limits the quality factor of nanomechanical graphene drums and turns them into potential test beds for Fermi-Pasta-Ulam physics. We find the thermalization rate Gamma to be independent of radius and scaling as Gamma similar to T* /is an element of(2)(pre), where T* and is an element of(pre) are effective resonator temperature and prestrain.
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| 8. |
- Midtvedt, Daniel, 1988, et al.
(författare)
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Multi-scale approach for strain-engineering of phosphorene
- 2017
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Ingår i: Journal of Physics Condensed Matter. - 0953-8984 .- 1361-648X. ; 29:18, s. Article nr 185702 -
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Tidskriftsartikel (refereegranskat)abstract
- A multi-scale approach for the theoretical description of deformed phosphorene is presented. This approach combines a valence-force model to relate macroscopic strain to microscopic displacements of atoms and a tight-binding model with distance-dependent hopping parameters to obtain electronic properties. The resulting self-consistent electromechanical model is suitable for large-scale modeling of phosphorene devices. We demonstrate this for the case of inhomogeneously deformed phosphorene drum, which may be used as an exciton funnel.
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| 9. |
- Midtvedt, Daniel, 1988, et al.
(författare)
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Nonlinear phononics using atomically thin membranes
- 2014
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 5, s. Article No. 4838 -
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Tidskriftsartikel (refereegranskat)abstract
- Phononic crystals and acoustic metamaterials are used to tailor phonon and sound propagation properties by utilizing artificial, periodic structures. Analogous to photonic crystals, phononic band gaps can be created, which influence wave propagation and, more generally, allow engineering of the acoustic properties of a system. Beyond that, nonlinear phenomena in periodic structures have been extensively studied in photonic crystals and atomic Bose-Einstein condensates in optical lattices. However, creating nonlinear phononic crystals or nonlinear acoustic metamaterials remains challenging and only few examples have been demonstrated. Here, we show that atomically thin and periodically pinned membranes support coupled localized modes with nonlinear dynamics. The proposed system provides a platform for investigating nonlinear phononics.
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| 10. |
- Midtvedt, Daniel, 1988, et al.
(författare)
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Strain-displacement relations for strain engineering in single-layer 2d materials
- 2016
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Ingår i: 2D Materials. - : IOP Publishing. - 2053-1583. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the electromechanical coupling in single-layer 2d materials. For non-Bravais lattices, we find important corrections to the standard macroscopic strain-microscopic atomic-displacement theory. We put forward a general and systematic approach to calculate strain-displacement relations for several classes of 2d materials. We apply our findings to graphene as a study case, by combining a tight binding and a valence force-field model to calculate electronic and mechanical properties of graphene nanoribbons under strain. The results show good agreement with the predictions of the Dirac equation coupled to continuum mechanics. For this long wave-limit effective theory, we find that the strain-displacement relations lead to a renormalization correction to the strain-induced pseudo-magnetic fields. A similar renormalization is found for the strain-induced band-gap of black phosphorous. Implications for nanomechanical properties and electromechanical coupling in 2d materials are discussed.
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