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Gustafsson M.V.,Chalmers University of Technology | Santos P.V.,Paul Drude Institute for Solid State Electronics | Johansson G.,Chalmers University of Technology | Delsing P.,Chalmers University of Technology
Nature Physics | Year: 2012

In the same way that micro-mechanical resonators resemble guitar strings and drums, surface acoustic waves resemble the sound these instruments produce, but moving over a solid surface rather than through air. In contrast with oscillations in suspended resonators, such propagating mechanical waves have not before been studied near the quantum mechanical limits. Here, we demonstrate local probing of surface acoustic waves with a displacement sensitivity of 30am RMS Hz -1/2 and detection sensitivity on the single-phonon level after averaging, at a frequency of 932MHz. Our probe is a piezoelectrically coupled single-electron transistor, which is sufficiently fast, non-destructive and localized to enable us to track pulses echoing back and forth in a long acoustic cavity, self-interfering and ringing the cavity up and down. We project that strong coupling to quantum circuits will enable new experiments, and hybrids using the unique features of surface acoustic waves. Prospects include quantum investigations of phonon-phonon interactions, and acoustic coupling to superconducting qubits for which we present favourable estimates. © 2012 Macmillan Publishers Limited. All rights reserved.


Kaganer V.M.,Paul Drude Institute for Solid State Electronics | Sabelfeld K.K.,Russian Academy of Sciences
Acta Crystallographica Section A: Foundations of Crystallography | Year: 2010

X-ray diffraction peak profiles are calculated by the Monte Carlo method for arbitrarily correlated dislocations without making any approximations or simplifications. The arrangement of dislocations in pairs with opposite Burgers vectors provides screening of the long-range strains. Moreover, any screening can be modeled by appropriate distribution of the dislocation pairs. Analytical description of the peak profiles is compared with the Monte Carlo results. Symmetric peaks due to screw dislocations and asymmetric peaks due to edge dislocations are simulated and analyzed. © 2010 International Union of Crystallography Printed in Singapore - all rights reserved.


Cohen K.,Hebrew University of Jerusalem | Rapaport R.,Hebrew University of Jerusalem | Santos P.V.,Paul Drude Institute for Solid State Electronics
Physical Review Letters | Year: 2011

In this Letter we suggest a method to observe remote interactions of spatially separated dipolar quantum fluids, and in particular, of dipolar excitons in GaAs bilayer based devices. The method utilizes the static electric dipole moment of trapped dipolar fluids to induce a local potential change on spatially separated test dipoles. We show that such an interaction can be used for model-independent, objective fluid density measurements, an outstanding problem in this field of research, as well as for interfluid exciton flow control and trapping. For a demonstration of the effects on realistic devices, we use a full two-dimensional hydrodynamical model. © 2011 American Physical Society.


Kleinert P.,Paul Drude Institute for Solid State Electronics
Physics Reports | Year: 2010

In the linear response regime close to equilibrium, the fluctuation-dissipation theorem relates linear transport coefficients via the well-known Green-Kubo or Einstein relation. The latter embodies a deep connection between fluctuations causing diffusion and dissipation, which are responsible for a finite mobility. Far from equilibrium, however, the Einstein relation is no longer valid so that both the mobility and diffusivity gain their own physical integrity. Consequently, beyond a linear response, both quantities have to be described by different approaches. Unfortunately, there is a strong imbalance of research activities devoted to the study of both transport mechanisms in semiconductors. On one hand, the rich physics of high-field quantum drift in semiconducting structures has a long history and has reached a high level of sophistication. On the other hand, there are only comparatively few and unsystematic studies that cover quantum diffusion of carriers under high-field conditions. This review aims at reducing this gap by presenting a unified approach to quantum drift and quantum diffusion. Starting from a semi-phenomenological basis, a quantum theory of transport coefficients is developed for one- as well as multi-band models. Physical implications are illustrated by selected applications whereby the quantum character of the approach is emphasized. Furthermore, the basic unified treatment of transport coefficients is extended by accounting for the two-time dependence of one-particle correlation functions in quantum statistics. As an application, a phononless transport mechanism is identified, which solely originates from the double-time nature of the evolution. Finally, additional examples are presented that illustrate the important role played by quantum diffusion in semiconductor physics. © 2009 Elsevier B.V.


Fernandez-Garrido S.,Paul Drude Institute for Solid State Electronics | Zettler J.K.,Paul Drude Institute for Solid State Electronics | Geelhaar L.,Paul Drude Institute for Solid State Electronics | Brandt O.,Paul Drude Institute for Solid State Electronics
Nano Letters | Year: 2015

We use line-of-sight quadrupole mass spectrometry to monitor the spontaneous formation of GaN nanowires on Si during molecular beam epitaxy. We find that the temporal evolution of nanowire ensembles is well described by a double logistic function. The analysis of the temporal evolution of nanowire ensembles, prepared under a wide variety of growth conditions, allows us to construct a growth diagram that can be used to predict the average delay time that precedes nanowire formation. © 2015 American Chemical Society.


Bierwagen O.,Paul Drude Institute for Solid State Electronics
Semiconductor Science and Technology | Year: 2015

The present review takes a semiconductor physics perspective to summarize the state-of-the art of In2O3 in relation to applications. After discussing conventional and novel applications, the crystal structure, synthesis of single-crystalline material, band-structure and optical transparency are briefly introduced before focussing on the charge carrier transport properties. The issues of unintentional n-type conductivity and its likely causes, the surface electron accumulation, and the lack of p-type conductivity will be presented. Intentional doping will be demonstrated to control the electron concentration and resistivity over a wide range, but is also subject to compensation. The control of the surface accumulation in relation to Schottky and ohmic contacts will be demonstrated. In the context of scattering mechanisms, the electron mobility and its limits will be discussed. Finally, the Seebeck coefficient and its significance will be shown, and ferromagnetic doping of In2O3 will be critically discussed. With this overview most if not all ingredients for the use of In2O3 as semiconductor material in novel or improved conventional devices will be given. © 2015 IOP Publishing Ltd.


Takagaki Y.,Paul Drude Institute for Solid State Electronics
Journal of Physics Condensed Matter | Year: 2012

Conductance modulations in wide-narrow-wide electron waveguides constructed from a two-dimensional topological insulator are investigated numerically. The conductance exhibits the Fabry-Perot oscillation at the opening of the helical edge states in the narrow segment when the potential offset imposed in the segment is varied. The quantum multiple reflections between the two ends of the narrow segment manifested by the oscillation demonstrate that the topological states are not protected from the scattering caused by an abrupt change in the channel width. The bulk states do not affect the vulnerability against the geometry scattering but they give rise to resonant transmission in an unconventional fashion. © 2012 IOP Publishing Ltd.


Kaganer V.M.,Paul Drude Institute for Solid State Electronics | Belov A.Yu.,Russian Academy of Sciences
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

Lattice distortions in a cylindrical nanowire with nonuniform intrinsic strains arbitrarily varying along its axis are analyzed, with a special emphasis on heterostructures. We find that, as a result of the elastic relaxation on the side surface, the lateral mismatch does not change the average longitudinal lattice period of the whole cylinder, but effects the average period of heterostructure. As a consequence, the positions of the x-ray diffraction peaks due to a periodic axial heterostructure depend on the ratio of the total height of the whole heterostructure to the cylinder diameter. The peaks attain the positions of the planar heterostructure peaks only when the diameter becomes orders of magnitude larger than the heterostructure height. The typical nanowire heterostructure parameters correspond to the opposite limit of full lateral relaxation. © 2012 American Physical Society.


Takagaki Y.,Paul Drude Institute for Solid State Electronics
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We numerically calculate the conductance of a topological insulator confined as quasi-one-dimensional strips using a four-band Hamiltonian. The conductance is nearly unchanged in the presence of a short-range disorder when the Fermi level is located in the bulk band gap. Helical edge states of topological insulators are no longer protected against the disorder, and scattering takes place if the bulk state coexists. Both the magnitude of conductance fluctuations and the average conductance are found to vary nonmonotonically in the latter regime with the strength of disorder, where the fluctuation amplitude is reduced when the average conductance is around 2e2/h. The scattering of the topological states is hence evidenced to be nontrivially affected by the coupling with the bulk state. © 2012 American Physical Society.


Calarco R.,Paul Drude Institute for Solid State Electronics
Materials | Year: 2012

An overview on InN nanowires, fabricated using either a catalyst-free molecular beam epitaxy method or a catalyst assisted chemical vapor deposition process, is provided. Differences and similarities of the nanowires prepared using the two techniques are presented. The present understanding of the growth and of the basic optical and transport properties is discussed. © 2012 by the authors.

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