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- Berggren, Karl-Fredrik, 1937-, et al.
(author)
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Effects of electron interactions at crossings of Zeeman-split subbands in quantum wires
- 2005
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 71:11, s. 115303-1-115303-5
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Journal article (peer-reviewed)abstract
- Recent experimental studies of Zeeman-split one-dimensional subbands in ballistic quantum wires in an in-plane magnetic field show that additional nonquantized conductance structures occur as subbands cross at low electron densities [A. C. Graham et al., Phys. Rev.Lett. 91, 136404 (2003)]. These structures are called 0.7 analogs. We analyze the experimental transconductance data within the Kohn-Sham spin-density-functional method, including exchange and correlation effects for an infinite split-gate quantum wire in a parallel, in-plane magnetic field B∥. Energy levels are found to rearrange abruptly as they cross due to polarization effects driven by exchange and Coulomb interactions. Experimental qualitative features are explained well by this model. ©2005 The American Physical Society.
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| 8. |
- Berggren, Karl-Fredrik, 1937-, et al.
(author)
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Electrical Resonance Circuits as Analogs to Quantum Mechanical Billiards
- 2006
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In: Acta Physica Polonica. A. - 0587-4246 .- 1898-794X. ; 109, s. 33-42
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Journal article (peer-reviewed)abstract
- We propose that a two-dimensional electric network may be used for fundamental studies of wave function properties, transport, and related statistics. Using Kirchhoff 's current law and the jw-method we find that the network is analogous to a discretized Schrodinger equation for quantum billiards and clots. Thus the complex electric potentials play the role of quantum rnechanical wave functions.
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- Berggren, Karl-Fredrik, 1937-, et al.
(author)
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Electron transport and Nanomagnetism
- 2008
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In: Nordforsk Network in Nanospintronics Theory and Simulations,2008.
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Conference paper (other academic/artistic)abstract
- Electron states, local magnetization and conductance in realistic quantum point contacts (QPCs) with different geometry and applied gate voltages will be discussed for a model GaAs/AlGaAs device. Using the local spin density approximation (LSDA) we recover ferromagnetic spatially split solutions in the pinch-off regime as well as antisymmetric solutions that occur with increasing voltage. These kind of spin states, which may appear in a repeated fashion in the few electron regime, are precursors to an extended ferromagnetic state that may be associated with the 0.7 (2e2/h) conductance anomaly. As the length of the QPC increases, so does the spin polarization and the difference in conductance between up-spin and down-spin electrons, resulting in movement of 0.7 anomaly towards the value of 0.5 (2e2/h). Due to the strong ferromagnetic spin polarization in a long QPC it will effectively work as a spin filter which may be useful for spintronics application.
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- Berggren, Karl-Fredrik, 1937-, et al.
(author)
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Nature of electron states and symmetry breaking in quantum point contacts according to the local spin density approximation
- 2008
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 20:16
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Journal article (peer-reviewed)abstract
- Electron states and local magnetization in quantum point contacts (QPCs) with different geometries and applied gate voltages are examined for a model GaAs/AlGaAs device. Using the local spin density approximation (LSDA) we recover ferromagnetic spatially split solutions in the pinch-off regime as well as antisymmetric solutions that occur with decreasing gate voltage. These kinds of spin states, which may appear in a repeated fashion in the few-electron regime, are precursors to an extended ferromagnetic state that may be associated with the 0.7 conductance anomaly. We briefly comment on some recent experiments indicating the presence of bound states (Yoon et al 2007 Phys. Rev. Lett. 99 136805). We have not found any indication of such states but suggest that the accumulations of spin and charge at the two ends of a QPC and associated singlet and triplet states are relevant in this context. © 2008 IOP Publishing Ltd.
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- Berggren, Karl-Fredrik, et al.
(author)
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Nature of streamlines for Berry-type wave functions in open 3D cavities
- 2009
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In: MATHEMATICAL MODELING OF WAVE PHENOMENA. - : American Institute of Physics (AIP). - 9780735406438 ; , s. 253-259
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Conference paper (peer-reviewed)abstract
- We explore preliminary a 3D wave cavity in which the interior complex wave functions are of Berry-type. Streamlines and novel disc-like features are uncovered by means of selective and interactive visualization.
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- Berggren, Karl-Fredrik
(author)
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NSC during 20 years
- 2009
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Conference paper (other academic/artistic)
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| 20. |
- Berggren, Karl-Fredrik, 1937-, et al.
(author)
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Quantum cellular automata - Theory, experimentation and prospects
- 2006
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In: Quantum Cellular Automata. - London : Imperial College Press. - 1860946321 - 9781860946325 ; , s. -300
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Book chapter (other academic/artistic)abstract
- The Quantum Cellular Automaton (QCA) concept represents an attempt to break away from the traditional three-terminal device paradigm that has dominated digital computation. Since its early formulation in 1993 at Notre Dame University, the QCA idea has received significant attention and several physical implementations have been proposed. This book provides a comprehensive discussion of the simulation approaches and the experimental work that have been undertaken on the fabrication of devices capable of demonstrating the fundamentals of QCA action. Complementary views of future perspectives for QCA technology are presented, highlighting a process of realistic simulation and of targeted experiments that can be assumed as a model for the evaluation of future device proposals.Show more Show less
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| 21. |
- Berggren, Karl-Fredrik, et al.
(author)
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Quantum stress in chaotic billiards
- 2008
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In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1063-651X .- 1095-3787. ; 77:066209
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Journal article (peer-reviewed)abstract
- This paper reports on a joint theoretical and experimental study of the Pauli quantum-mechanical stress tensor T(x,y) for open two-dimensional chaotic billiards. In the case of a finite current flow through the system the interior wave function is expressed as =u+iv. With the assumption that u and v are Gaussian random fields we derive analytic expressions for the statistical distributions for the quantum stress tensor components T. The Gaussian random field model is tested for a Sinai billiard with two opposite leads by analyzing the scattering wave functions obtained numerically from the corresponding Schrödinger equation. Two-dimensional quantum billiards may be emulated from planar microwave analogs. Hence we report on microwave measurements for an open two-dimensional cavity and how the quantum stress tensor analog is extracted from the recorded electric field. The agreement with the theoretical predictions for the distributions for T(x,y) is quite satisfactory for small net currents. However, a distinct difference between experiments and theory is observed at higher net flow, which could be explained using a Gaussian random field, where the net current was taken into account by an additional plane wave with a preferential direction and amplitude.
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| 23. |
- Berggren, Karl-Fredrik, 1937-, et al.
(author)
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Simulation of the time-dependent behavior of QCA circuits
- 2006
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In: Quantum Cellular Automata. - London : Imperial Press. - 1860946321 - 9781860946325 ; , s. -300
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Book chapter (other academic/artistic)abstract
- The Quantum Cellular Automaton (QCA) concept represents an attempt to break away from the traditional three-terminal device paradigm that has dominated digital computation. Since its early formulation in 1993 at Notre Dame University, the QCA idea has received significant attention and several physical implementations have been proposed. This book provides a comprehensive discussion of the simulation approaches and the experimental work that have been undertaken on the fabrication of devices capable of demonstrating the fundamentals of QCA action. Complementary views of future perspectives for QCA technology are presented, highlighting a process of realistic simulation and of targeted experiments that can be assumed as a model for the evaluation of future device proposals.
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| 30. |
- Fräjdin-Hellqvist, Ulla-Britt, et al.
(author)
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Missa inte chansen med ESS
- 2005
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In: Ny teknik. - 0550-8754. ; :24
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Journal article (pop. science, debate, etc.)
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| 37. |
- Sadreev, Almas F, et al.
(author)
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Signatures of quantum chaos in complex wavefunctions describing open billiards
- 2005
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In: Journal of Physics A. - : IOP Publishing. - 0305-4470 .- 1361-6447. ; 38:49, s. 10787-10804
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Journal article (peer-reviewed)abstract
- We discuss signatures of quantum chaos in open chaotic billiards. Solutions for such a system are given by complex scattering wavefunctions ψ ≤ u + iv when a steady current flows through the billiard. For slightly opened chaotic billiards the current distributions are simple and universal. It is remarkable that the resonant transmission through integrable billiards also gives the universal current distribution. Currents induced by the Rashba spin-orbit interaction can flow even in closed billiards. Wavefunction and current distributions for a chaotic billiard with weak and strong spin-orbit interactions have been derived and compared with numerics. Similarities with classical waves are considered. In particular we propose that the networks of electric resonance RLC circuits may be used to study wave chaos. However, being different from quantum billiards, there is a resistance from the inductors which gives rise to heat power and decoherence. © 2005 IOP Publishing Ltd.
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| 41. |
- Yakimenko, Irina I, et al.
(author)
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The Influence of Many-Body Interactions on the Electron States in Quantum Point Contacs : Persistence of Exchange-Driven Splitting at High External Magnetic Fields
- 2009
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In: JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM. - : Springer Science and Business Media LLC. - 1557-1939 .- 1557-1947. ; 22:5, s. 449-454
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Journal article (peer-reviewed)abstract
- Spontaneous spin polarization of a quasi-1D electron gas in quantum point contacts (QPCs) is an important concept when analyzing conductance anomalies in the quantum limit. As suggested by recent measurements (Koop et al., J. Supercond. Nov. Magn. 20:433, 2007) there is a splitting of the subband levels in QPCs related to 0.7 conductance anomaly, both for zero- and finite in-plane magnetic fields. In the present paper we present theoretical results for spin polarization occurring in a QPC in a magnetic field as obtained from the local spin-density approximation (LSDA). Our numerical simulations are consistent with the findings of Koop et al. and support the idea that spin polarization underpins the conductance anomaly.
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