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| 5. |
- Berggren, Karl-Fredrik, 1937-, et al.
(författare)
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Effects of electron interactions at crossings of Zeeman-split subbands in quantum wires
- 2005
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 71:11, s. 115303-1-115303-5
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Berggren, Karl-Fredrik, 1937-, et al.
(författare)
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Electrical Resonance Circuits as Analogs to Quantum Mechanical Billiards
- 2006
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Ingår i: Acta Physica Polonica. A. - 0587-4246 .- 1898-794X. ; 109, s. 33-42
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Berggren, Karl-Fredrik, 1937-, et al.
(författare)
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Electron transport and Nanomagnetism
- 2008
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Ingår i: Nordforsk Network in Nanospintronics Theory and Simulations,2008.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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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| 9. |
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| 10. |
- Berggren, Karl-Fredrik, 1937-
(författare)
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Fysik
- 2012. - 1
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Ingår i: Naturvetarguiden. - Nacka : Naturvetarna. - 9789163704130
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Bokkapitel (populärvet., debatt m.m.)
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| 11. |
- Berggren, Karl-Fredrik, 1937-
(författare)
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Förolämpande och konspiratorisk - debattinlägg
- 2005
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Ingår i: Sydsvenska Dagbladet. - Malmö : Sydsvenska dagbladets AB. ; 28 maj 2005, s. C2-C3
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 12. |
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| 13. |
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| 14. |
- Berggren, Karl-Fredrik, 1937-, et al.
(författare)
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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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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 20:16
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Tidskriftsartikel (refereegranskat)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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| 17. |
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| 18. |
- Berggren, Karl-Fredrik, 1937-, et al.
(författare)
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Quantum cellular automata - Theory, experimentation and prospects
- 2006
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Ingår i: Quantum Cellular Automata. - London : Imperial College Press. - 1860946321 - 9781860946325 ; , s. -300
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Bokkapitel (övrigt vetenskapligt/konstnärligt)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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| 19. |
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| 20. |
- Berggren, Karl-Fredrik, 1937-, et al.
(författare)
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Simulation of the time-dependent behavior of QCA circuits
- 2006
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Ingår i: Quantum Cellular Automata. - London : Imperial Press. - 1860946321 - 9781860946325 ; , s. -300
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Bokkapitel (övrigt vetenskapligt/konstnärligt)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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| 21. |
- Berggren, Karl-Fredrik, 1937-, et al.
(författare)
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Sverige rustar för neutronkamp
- 2007
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Ingår i: Fysikaktuellt. - 0283-9148. ; :3, s. 14-15
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
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| 22. |
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| 23. |
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| 24. |
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| 25. |
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| 26. |
- Fräjdin-Hellqvist, Ulla-Britt, et al.
(författare)
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Missa inte chansen med ESS
- 2005
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Ingår i: Ny teknik. - 0550-8754. ; :24
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 27. |
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| 28. |
- Hamberg, Ivar, et al.
(författare)
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Band-gap widening in heavily Sn-daped In203
- 1984
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Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 30:6, s. 3240-3249
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Tidskriftsartikel (refereegranskat)abstract
- Films of pure and Sn-doped semiconducting Inz03 were prepared by reactive e-beam evaporation. The spectral absorption coefficient was evaluated by spectrophotometry in the (2—6)-eV range. The extracted band gap increases with electron density (ne ) approximately as ne 2/3 for ne ≤10-21 cm-3 . This result is interpreted within an effective-mass model for n-doped semiconductors well above the Mott critical density. Because of the high degree of doping, the impurities are ionized and the associated electrons occupy the bottom of the conduction band in the form of an electron gas. The model accounts for a Burstein-Moss shift as well as electron-electron and electron-impurity scattering treated in the random-phase approximation. Experiments and theory were reconciled by assuming a parabolic valence band with an effective mass -0.6m. Earlier work on doped oxide semiconductors are assessed in the light of the present results.
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| 29. |
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| 30. |
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| 31. |
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| 32. |
- Jones, A., et al.
(författare)
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Chapter 5: Signatures of Spin Polarization In Four-Gate Quantum Point Contact Structures
- 2017
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Ingår i: Contemporary Topics in Semiconductor Spintronics. - : World Scientific. ; , s. 123-158
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Bokkapitel (refereegranskat)abstract
- Using a Non-equilibrium Green’s function (NEGF) approach, a set of experiments is suggested which can provide indirect evidence of the fine and non-local electrostatic tuning of the onset of spin polarization in two closely spaced quantum point contacts (QPCs) with two sets of in-plane side gates (SGs) in the presence of lateral spin-orbit coupling (LSOC). The conductance of the two closely spaced QPCs or four-gate QPC is studied for different biasing conditions applied to two leftmost and rightmost SGs. When calculated as a function of the common sweep voltage Vsweep applied to two of the SGs, the conductance plots show several conductance anomalies, i.e., below G0 = 2e2/h, characterized by intrinsic bistability, i.e., hysteresis loops due to a difference in the conductance curves for up and down sweeps of the common gate voltage. The hysteresis loops are related to the co-existence of multistable spin textures in the narrow channel of the four-gate QPC and are very sensitive to the biasing conditions on the four SGs. The shape of the conductance anomalies and size of hysteresis loops are different when the biasing conditions on the leftmost and rightmost SGs are swapped. This rectifying behavior is an additional indirect evidence for the onset of spontaneous spin polarization in nanoscale devices made of QPCs. These results show that the onset and fine tuning of conductance anomalies in QPC structures are highly sensitive to the non-local action of closely spaced SGs. This effect must therefore be taken into account in the design of all electrical spin valves making use of middle gates to fine tune the spin precession between QPC based spin injector and detector contacts.
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| 33. |
- Sadreev, Almas F, et al.
(författare)
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Signatures of quantum chaos in complex wavefunctions describing open billiards
- 2005
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Ingår i: Journal of Physics A. - : IOP Publishing. - 0305-4470 .- 1361-6447. ; 38:49, s. 10787-10804
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Tidskriftsartikel (refereegranskat)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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| 34. |
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| 35. |
- Sernelius, Bo, 1948-, et al.
(författare)
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Band-gap tailoring of Zno by means of heavy Al doping
- 1988
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Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 37:17, s. 10244-10248
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Tidskriftsartikel (refereegranskat)abstract
- Films of ZnO:Al were produced by weakly reactive dual-target magnetron sputtering. Optical band gaps, evaluated from spectrophotometric data, were widened in proportion to the Al doping.The widening could be quantitatively reconciled with an effective-mass model for n-doped semiconductors, provided the polar character of ZnO was accounted for.
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| 36. |
- Tellander, Felix B. A., et al.
(författare)
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Non-Hermitian Wave Mechanics: An Unorthodox Way into Embedded Systems
- 2017
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Ingår i: Journal of Young Investigators. - : Journal of Young Investigators. - 1539-4026. ; 33, s. 24-27
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Tidskriftsartikel (refereegranskat)abstract
- This review outlines an unconventional but timely formulation of quantum dynamics of systems in contact with an environment. This alternative approach to traditional quantum mechanics is generic and is currently gaining attention in a number of fields as, for example, quantum scattering and transport, optical waveguides, devices embedded in an environment, oscillatory classical systems, RLC circuits and other open systems with loss and gain. Here we briefly outline this formulation in which the condition of space-time reflection (PT-symmetry) plays a central role. If PT-symmetry is broken upon parametric change, real energy levels generally turn complex. At the onset of such a symmetry breaking levels coalesce at “Exceptional Points” (EP).
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| 37. |
- Tellander, Felix B. A., et al.
(författare)
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Probability Current and a Simulation of Particle Separation
- 2016
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Ingår i: Journal of Young Investigators. - : Journal of Young Investigators. - 1539-4026. ; 31, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- The structure of scattered wave fields and currents is of interest in a variety of fields within physics such as quantum mechanics and optics. Traditionally two-dimensional structures have been investigated; here we focus on three-dimensional structures. We make a generic study of three dimensional quantum box cavities, and our main objective is to visualize the probability current. Visualizations are achieved for complex linear combinations of wave functions with different excitations and with boundary conditions: Dirichlet, Neumann, and mixed. By using different boundary conditions, the results reported here are relevant to many different wave analogues such as microwave billiards and acoustic cavities. Visualization was mainly done through animated images, but a chaotic state was visualized by 3D printing. Our results suggest that if the state of excitation is the same in the different boundary conditions, the current is the same, except at the boundaries of the box. Application to sort nanoparticles in acoustic cavities is considered.
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| 38. |
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| 39. |
- Yakymenko, Ivan, et al.
(författare)
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Basic modelling of effects of geometry and magnetic field for quantum wires injecting electrons into a two-dimensional electron reservoir
- 2019
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Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 0953-8984 .- 1361-648X. ; 31:34
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Tidskriftsartikel (refereegranskat)abstract
- High-mobility two-dimensional electron gas (2DEG) which resides at the interface between GaAs and AlGaAs layered semiconductors has been used experimentally and theoretically to study ballistic electron transport. The present paper is motivated by recent experiments in magnetic electron focusing. The proposed device consists of two quantum point contacts (QPCs) serving as electron injector and collector which are placed in the same semiconductor GaAs/AlGaAs heterostructure. Here we focus on a theoretical study of the injection of electrons via a quantum wire/QPC into an open two-dimensional (2D) reservoir. The transport is considered for non-interacting electrons at different transmission regimes using the mode-matching technique. The proposed mode-matching technique has been implemented numerically. Electron flow through the quantum wire with hard-wall rectangular, conical and rounded openings has been studied. We have found for these three cases that the geometry of the opening does not play a crucial role for the electron propagation. When a perpendicular magnetic field is applied the electron paths in the 2D reservoir are curved. We analyse this case both classically and quantum-mechanically. The effect of spin-splitting due to exchange interactions on the electron flow is also considered. The effect is clearly present for realistic choices of device parameters and consistent with observations. The results of this study may be applied in designing magnetic focusing devices and spin separation.
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| 40. |
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