| 1. |
- Bankel, Johan, et al.
(författare)
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The CDIO syllabus: a comparative study of expected student proficiency
- 2003
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Ingår i: European Journal of Engineering Education. - : Taylor & Francis. - 0304-3797 .- 1469-5898. ; 28:3, s. 297-315
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Tidskriftsartikel (refereegranskat)abstract
- Engineering students must graduate with command of a vast body of technical knowledge. They must possess personal, interpersonal and system-building skills to function in teams, and be prepared to produce products and systems. Their education must have been structured under a curriculum blending ability to combine technical expertise with ethical, innovative, philosophical and humanistic acumen. This paper describes a unique international collaboration among four universities to reform engineering education. The collaborators agreed to a statement of goals, which includes descriptions of knowledge, skills and attitudes vital to an effective education, and codifies proficiency levels expected of graduates. We developed and utilized unique stakeholder surveys both to validate our prototype and to determine desired proficiency levels. This collaboration resulted in The CDIO Syllabus, A Statement of Goals for Undergraduate Engineering Education. The syllabus is both a template and a process that can be used to customize the syllabus to others' programmes. It can define new educational initiatives/and be employed as the basis for rigorous assessment. This paper details how, with the input of industry, academia and others, we employed an engineering problem-solving paradigm to effect our redesign. It outlines the syllabus and the unique process employed to create it.
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| 2. |
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| 3. |
- Berggren, Karl-Fredrik, et al.
(författare)
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Chaos in a quantum dot with spin-orbit coupling
- 2001
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Ingår i: Foundations of physics. - 0015-9018 .- 1572-9516. ; 31:2, s. 233-242
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Tidskriftsartikel (refereegranskat)abstract
- Level statistics are nodal point distribution in a rectangular semiconductor quantum dot are studies for different degrees of spin-orbit coupling. The chaotic features occurring from the spin-orbit coupling have no classical counterpart. Using experimental values of GaSb/InAs/GaSb semiconductor quantum wells we find that level repulsion can lead to the semi-Poisson distribution for nearest level separations. Nodal lines and nodal points are also investigated. Comparison is made with nodal point distributions for fully chaotic states.
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| 4. |
- Berggren, Karl-Fredrik, et al.
(författare)
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Crossover from regular to irregular behavior in current flow through open billiards
- 2002
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Ingår i: Physical Review E - Statistical, Nonlinear, and Soft Matter Physics. - 1539-3755. ; 66:1
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Tidskriftsartikel (refereegranskat)abstract
- We discuss signatures of quantum chaos in terms of distributions of nodal points, saddle points, and streamlines for coherent electron transport through two-dimensional billiards, which are either nominally integrable or chaotic. As typical examples of the two cases we select rectangular and Sinai billiards. We have numerically evaluted distribution functions for nearest distances between nodal points and found that there is a generic form for open chaotic billiards through which a net current is passed. We have also evaluated the distribution functions for nodal points with specific vorticity (winding number) as well as for saddle points. The distributions may be used as signatures of quantum chaos in open systems. All distributions are well reproduced using random complex linear combinations of nearly monochromatic states in nominally closed billiards. In the case of rectangular billiards with simple sharp-cornered leads the distributions have characteristic features related to order among the nodal points. A flaring or rounding of the contact regions may, however, induce a crossover to nodal point distributions and current flow typical for quantum chaos. For an irregular arrangement of nodal points, as for example in the Sinai billiard, the quantum flow lines become very complex and volatile, recalling chaos among classical trajectories. Similarities with percolation are pointed out. ©2002 The American Physical Society.
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| 5. |
- Berggren, Karl-Fredrik, et al.
(författare)
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Effects of exchange and electron correlation on conductance and nanomagnetism in ballistic semiconductor quantum point contacts
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:8
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Tidskriftsartikel (refereegranskat)abstract
- The spontaneous magnetization of a quantum point contact (QPC) formed between two large quantum dots by a lateral confinement of a high-mobility two-dimensional electron gas is studied for a realistic GaAs/AlxGa1-xAs heterostructure. The model of the device incorporates the contributions from a patterned gate, doping, surface states, and mirror charges. To explore the magnetic properties, the Kohn-Sham local spin-density formalism is used with exchange and correlation potentials that allows for local spin polarization. Exchange is the dominant mechanism behind local magnetization within the QPC, while the correlation part is less prominent. However, the correlation potential gives rise to an important correction in the QPC potential. Below the first conduction plateau we thus find a magnetized regime corresponding approximately to a single electron spin. Using an approximate separable saddle potential we compute the conductance and recover the so-called similar to0.7 (2e(2)/h) conduction anomaly plus an additional anomaly at similar to0.4 (2e(2)/h) below which the magnetization collapses.
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| 6. |
- Berggren, Karl-Fredrik, et al.
(författare)
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New directions with fewer dimensions
- 2002
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Ingår i: Physics world. - 0953-8585 .- 2058-7058. ; 15:10, s. 37-42
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Tidskriftsartikel (refereegranskat)
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| 7. |
- Berggren, Karl-Fredrik, et al.
(författare)
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On the role of electron exchange and correlation in semiconductor quantum dots
- 2001
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 12:4, s. 529-532
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Spontaneous magnetization of single and coupled quantum dots formed by lateral confinement of a high-mobility two-dimensional electron gas is studied for a realistic GaAs/AlGaAs heterostructure. The modelling of the device takes into account contributions from a patterned gate, doping, surface states, and mirror charges. To explore the magnetic properties we use the Kohn-Sham local spin-density formalism including the contributions from electron correlation and exchange. We show by explicit calculations that the exchange is the dominant mechanism driving a spontaneous magnetization of a dot. The correlation potential reduces the amount of level splitting and usually affects the electron content in the dot at a given gate voltage. These effects are, however, small and may be neglected under present circumstances. Single dots with up to 50 electrons have been studied.
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| 8. |
- Berggren, Karl-Fredrik, et al.
(författare)
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Quantum chaos among nodal points and streamlines at ballistic electron transport through open quantum dots
- 2001
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 12:4, s. 562-565
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We trace signatures of quantum chaos in the distribution of nodal points and streamlines for coherent electron transport through different types of quantum dots (chaotic and regular). We have calculated normalized distribution functions for the nearest distances between nodal points and found that this distribution may be used as a signature of quantum chaos for electron transport in open systems. Different chaotic billiards show the same characteristic distribution function for nodal points. This signature of quantum chaos is well reproduced using well known approaches for chaotic wavefunctions. We have also investigated the quantum flows which display some remarkable features.
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| 9. |
- Bychkov, A.M., et al.
(författare)
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Spin-dependent electron behaviour in quantum point contacts
- 2000
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 11:4, s. 318-322
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Tidskriftsartikel (refereegranskat)abstract
- The effect of spontaneous spin polarization in quantum point contacts (QPCs) is investigated by self-consistent modelling within the Kohn-Sham local spin-density formalism. The existence of the spin-polarized state of the QPC channel in the low-density regime is shown to change the value and the shape of the effective potential barrier for up- and down-spin electrons. We suggest that this effect can be relevant to the explanation of the anomalous 0.7-structure in the QPC conductance and may assist spin injection in potential spintronic devices.
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| 10. |
- Graham, A.C., et al.
(författare)
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0.7 Analogue structures and exchange interactions in quantum wires
- 2004
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Ingår i: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 131:9-10 SPEC. ISS., s. 591-597
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Tidskriftsartikel (refereegranskat)abstract
- We present experimental studies of crossings of spin-split one-dimensional subbands in ballistic quantum wires in an in-plane magnetic field B ?. At low electron densities, a spontaneous spin-splitting occurs as subbands cross, which gives rise to additional non-quantised conductance structures called 0.7 analogues. We analyse the data within a spin-density-functional model, which includes exchange interactions in a magnetic field. Focussing on the region of the crossings of spin-split subbands, it is found that the energy levels rearrange as they cross due to exchange interactions. © 2004 Elsevier Ltd. All rights reserved.
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| 11. |
- Heyman, A., et al.
(författare)
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Band structure and spin polarization for a one-dimensional array of quantum point contacts
- 2004
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 15:1, s. 143-148
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Tidskriftsartikel (refereegranskat)abstract
- We have numerically studied the band structure and the spin polarization effect in a periodic one-dimensional array of quantum point contacts (QPCs) formed in a two-dimensional electron gas in a plane-layered semiconductor system. In this study we used a self-consistent model developed within the framework of the Kohn-Sham local spin-density formalism. We have found that the band structure contains a mixture of flat and dispersed bands, and the role of transverse modes in the formation of such a band structure has been clearly demonstrated. We have also shown that spin polarization occurs mainly in the regions occupied by the QPCs and that it is qualitatively similar to the spin polarization in a single QPC.
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| 12. |
- Ishio, H, et al.
(författare)
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Wave function statistics for ballistic quantum transport through chaotic open billiards : Statistical crossover and coexistence of regular and chaotic waves
- 2001
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1063-651X .- 1095-3787. ; 64:5, s. art. no.-056208
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Tidskriftsartikel (refereegranskat)abstract
- For ballistic transport through chaotic open billiards, we implement accurate fully quantal calculations of the probability distributions and spatial correlations of the local densities of single-electron wave functions within the cavity. We find wave-statistical behaviors intrinsically different from those in their closed counterparts. Chaotic-scattering wave functions in open systems can be quantitatively interpreted in terms of statistically independent real and imaginary random fields in the same way as for wave-function statistics of closed systems in the time-reversal symmetry-breaking crossover regime. We also discuss perceived statistical deviations, which are attributed to the coexistence of regular and chaotic waves and given analytical explanations.
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| 13. |
- Ishio, H., et al.
(författare)
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Wave function statistics for mesoscopic transport through chaotic open billiards : Time reversibility, space reciprocity breaking and statistical crossover
- 2001
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Ingår i: Computer Physics Communications. - 0010-4655 .- 1879-2944. ; 142:1-3, s. 64-70
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We investigate the probability distributions and spatial correlations of the local densities of electron wave functions for ballistic transport through mesoscopic chaotic open billiards. By quantitative comparison between our accurate fully-quantal calculations with theoretical expressions, we find wave-statistical behaviors intrinsically different from those in closed systems. It is shown that chaotic-scattering wave functions in open systems can be universally interpreted in terms of statistically independent real and imaginary random fields together with breaking of the endowed space reciprocity, resulting in the same wave function statistics as in the time-reversal symmetry-breaking crossover regime in closed systems. © 2001 Elsevier Science B.V. All rights reserved.
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| 14. |
- Jaksch, Peter, et al.
(författare)
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Realization of a two-qubit quantum gate utilizing edge states around antidots
- 2004
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Ingår i: International Journal of Nanoscience. - 0219-581X. ; 3:3, s. 309-319
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Tidskriftsartikel (refereegranskat)abstract
- It is known that a two-spin system with four energy levels can be used to realize a two-qubit quantum gate. A feasible realization of quantum gates should rely on stable quantum mechanical states. An example of such states are edge states which arise around regions with high potential in a strong magnetic field. In this paper we show that certain edge states around a pair of antidots may be suitable for quantum gate implementation.
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| 15. |
- Knisevskaja, L., et al.
(författare)
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Singular integral equations method for computations of the scattering characteristics of a model heart exposed to electromagnetic radiation
- 2003
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Ingår i: Applied Mathematics and Computation. - 0096-3003 .- 1873-5649. ; 138:2-3, s. 545-553
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Tidskriftsartikel (refereegranskat)abstract
- The singular integral equations method elaborated in this paper allows us to solve accurately the Maxwell’s equations for a three-dimensional (3D) model heart exposed to electromagnetic radiation in the frequency range SHF and EHF. To test our algorithm we have computed the back scattering cross-section for a metal disc. Our computations are in good agreement with experiment given in literature. To demonstrate the usefulness of the algorithm we have computed the scattering characteristics of a simplified model of the human heart. This model is composed of the myocardium, the right and left atria and ventricles. All surfaces of the model are defined a triangular mesh in 3D covering the heart surfaces and normals to the triangles.
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| 16. |
- Macucci, M., et al.
(författare)
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Status and perspectives of nanoscale device modelling
- 2001
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 12:2, s. 136-142
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- During the meetings of the theory and modelling working group, within the MEL-ARI (Microelectronics Advanced Research Initiative) and NID-FET (Nanotechnology Information Devices-Future and Emerging Technologies) initiatives of the European Commission, we have been discussing the current status and the future perspectives of nanoscale device modelling. The outcome of such a discussion is summarized in the present paper, outlining the major challenges for the future, such as the integration of nonequilibrium phenomena and of molecular-scale properties. We believe that modelling has a growing importance in the development of nanoelectronic devices and must therefore make a move from physics to engineering, providing valid design tools, with quantitative predictive capabilities.
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| 17. |
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| 18. |
- Onipko, AI, et al.
(författare)
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Scanning tunneling spectroscopy on pi-conjugated phenyl-based oligomers : A simple physical model
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 61:16, s. 11118-11124
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Tidskriftsartikel (refereegranskat)abstract
- The current-voltage (I-V) characteristics obtained by scanning tunneling spectroscopy (STS) on uncoated gold substrates and gold substrates coated with self-assembled monolayers of aromatic thiols are shown to be in good quantitative agreement with the Landauer-Buttiker approach to the heterojunction conductance. The self-assembled monolayers consist of one and three chained phenyl rings, forming an azomethine oligomer, both monomer and trimer are chemisorbed on gold via sulphur while terminated from the opposite side by an amine head group. It is found that if the electrostatic energy of the applied potential is ramped within the HOMO-LUMO energy gap (highest occupied molecular orbital-lowest unoccupied molecular orbital) the particular form of the apparent I-V relations reflect an interplay of (i) the WKB factor that accounts for the through-air tunneling between the STM tip and the coated/uncoated substrate, (ii) resonancelike structure of the tip-apex local density of states (LDOS), and (iii) the relative position and intensity of the HOMO and LUMO level peaks in the molecular LDOS. The latter two factors give rise to asymmetry of I-V characteristics. The tunneling spectroscopy measurements and their theoretical evaluation indicate that the STM tip probes a molecular carbon atom rather than the uppermost nitrogen, possibly due to plowing through the molecules. The findings of the work are supported by a close similarity of measured and calculated I(V) curves, which is obtained on different but genetically related samples, at different setpoints of the tunnel current, and with essentially one and the same set of parameters (inferred from experiments and semi-empirical self-consistent modeling of the molecular electronic structure).
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| 19. |
- Paul, D.J., et al.
(författare)
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n-type Si/SiGe resonant tunnelling diodes
- 2002
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Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 89:1-3, s. 26-29
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Resonant tunnelling diodes (RTDs) have been fabricated using Si/SiGe heterolayers which demonstrate room temperature performance comparable to III-V technology. Peak current densities up to 282 kA cm-2 with peak-to-valley current ratios (PVCRs) of 2.4 have been demonstrated at room temperature in devices with dimensions of 5 × 5 µm2. Scaling the device size demonstrates that the peak current density is inversely proportional to the device area. It is suggested that this is related to thermal limitations in the device structure. Estimates are also produced for the maximum frequency of oscillations of the diodes which suggest that oscillators may operate with speeds comparable to III-V diodes. © 2002 Elsevier Science B.V. All rights reserved.
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| 20. |
- Paul, D.J., et al.
(författare)
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Si/SiGe electron resonant tunneling diodes with graded spacer wells
- 2001
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:26, s. 4184-4186
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Tidskriftsartikel (refereegranskat)abstract
- Resonant tunneling diodes have been fabricated using graded Si1 - xGex (x = 0.3?0.0) spacer wells and strained Si0.4Ge0.6 barriers on a relaxed Si0.7Ge0.3 n-type substrate which demonstrates negative differential resistance at up to 100 K. This design is aimed at reducing the voltage at which the peak current density is achieved. Peak current densities of 0.08 A/cm2 with peak-to-valley current ratios of 1.67 have been achieved for a low peak voltage of 40 mV at 77 K. This represents an improvement of over an order of magnitude compared to previous work. © 2001 American Institute of Physics.
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| 21. |
- Paul, DJ, et al.
(författare)
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Si/SiGe electron resonant tunneling diodes
- 2000
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Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 77:11, s. 1653-1655
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Tidskriftsartikel (refereegranskat)abstract
- Resonant tunneling diodes have been fabricated using strained-Si wells and strained Si0.4Ge0.6 barriers on a relaxed Si0.8Ge0.2 n-type substrate, which demonstrate negative differential resistance at 298 K. Peak current densities of 5 kA/cm(2) with peak-to-valley current ratios of 1.1 have been achieved. Theoretical modeling of the structure demonstrates that the major current peak results from the tunneling of light-mass electrons from the relaxed substrate and not from the heavy-mass electrons in the emitter accumulation layer. (C) 2000 American Institute of Physics. [S0003- 6951(00)02337-8].
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| 22. |
- Sadreev, Almas, et al.
(författare)
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Current statistics for wave transmission through an open Sinai billiard: Effects of net currents
- 2004
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1063-651X .- 1095-3787. ; 70:2
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Tidskriftsartikel (refereegranskat)abstract
- Transport through quantum and microwave cavities is studied by analytic and numerical techniques. In particular, we consider the statistics for a finite net probability current (Poynting vector) flowing through an open ballistic Sinai billiard to which two opposite leads/wave guides are attached. We show that if the net probability current is small, the scattering wave function inside the billiard is well approximated by a Gaussian random complex field. In this case, the current statistics are universal and obey simple analytic forms. For larger net currents, these forms still apply over several orders of magnitudes. However, small characteristic deviations appear in the tail regions. Although the focus is on electron and microwave billiards, the analysis is relevant also to other classical wave cavities as, for example, open planar acoustic reverberation rooms, elastic membranes, and water surface waves in irregularly shaped vessels.
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| 23. |
- Saichev, AL, et al.
(författare)
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Distribution of nearest distances between nodal points for the Berry function in two dimensions
- 2001
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1063-651X .- 1095-3787. ; 64:3
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Tidskriftsartikel (refereegranskat)abstract
- According to Berry a wave-chaotic state may be viewed as a superposition of monochromatic plane waves with random phases and amplitudes. Here we consider the distribution of nodal points associated with this state. Using the property that both the real and imaginary parts of the wave function are random Gaussian fields we analyze the correlation function and densities of the nodal points. Using two approaches (the Poisson and Bernoulli) we derive the distribution of nearest neighbor separations. Furthermore the distribution functions for nodal points with specific chirality are found. Comparison is made with results from numerical calculations for the Berry wave function.
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| 24. |
- Saichev, A.I., et al.
(författare)
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Statistics of interior current distributions in two-dimensional open chaotic billiards
- 2002
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Ingår i: Journal of Physics A. - : IOP Publishing. - 0305-4470 .- 1361-6447. ; 35:7
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Tidskriftsartikel (refereegranskat)abstract
- The probability current statistics of two-dimensional open chaotic ballistic billiards is studied both analytically and numerically. Assuming that the real and imaginary parts of the scattering wave function are both random Gaussian fields, we find a universal distribution function for the interior probability current. As a by-product we recover previous analytic forms for wave function statistics. The expressions bridge the entire region from GOE to GUE type statistics. Our analytic expressions are verified numerically by explicit quantum mechanical calculations of transport through a Bunimovich billiard.
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| 25. |
- See, P., et al.
(författare)
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High performance Si/Si1-x Gex resonant tunneling diodes
- 2001
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Ingår i: IEEE Electron Device Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 0741-3106 .- 1558-0563. ; 22:4, s. 182-184
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Tidskriftsartikel (refereegranskat)abstract
- Resonant tunneling diodes (RTDs) with strained i-Si0.4 Ge06. potential barriers and a strained i-Si quantum well, all on a relaxed Si0.8 Ge0.2 virtual substrate were successfully grown by ultra high vacuum compatible chemical vapor deposition and fabricated using standard Si processing methods. A large peak to valley current ratio of 2.9 and a peak current density of 4.3 kA/cm2 at room temperature were recorded from pulsed and continuous dc current-voltage measurements, the highest reported values to date for Si/Si1-x Gex RTDs. These dc figures of merit and material system render such structures suitable and highly compatible with present high speed and low power Si/Si1-x Gex heterojunction field effect transistor based integrated circuits.
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| 26. |
- Starikov, Anton, et al.
(författare)
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Effects of accidental microconstriction on the quantized conductance in long wires
- 2003
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Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5023, s. 267-270
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We have investigated the conductance of long quantum wires formed in GaAs/ AlxGa1-x As heterostructures. Using realistic fluctuation potentials from donor layers we have simulated numerically the conductance of four different kinds of wires. While ideal wires show perfect quantization, potential fluctuations from random donors may give rise to strong conductance oscillations and degradation of the quantization plateaux. Statistically there is always the possibility of having large fluctuations in a sample that may effectively act as a microconstriction. We therefore introduce microconstrictions in the wires by occasional clustering of donors. These microconstrictions are found to restore the quantized plateaux. A similar effect is found for accidental lithographic inaccuracies.
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| 27. |
- Starikov, Anton, et al.
(författare)
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Scenario for the 0.7-conductance anomaly in quantum point contacts
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:23
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Tidskriftsartikel (refereegranskat)abstract
- Effects of spontaneous spin polarization in quantum point contacts (QPC's) are investigated for a realistic semiconductor device structure using the Kohn-Sham local spin-density formalism. At maximal polarization in the contact area, there is a bifurcation into ground-state and metastable solutions. The conduction associated with the metastability is lower than for the normal state. With increasing temperature, the conductance should therefore show an anomalous behavior as observed. For the present device we do not recover resonance or quasibound states.
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| 28. |
- Tamosiunas, V, et al.
(författare)
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Computation of electric field components and standing wave coefficient for a waveguide structure with a lowohm semiconductor plate
- 2000
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Ingår i: International journal of infrared and millimeter waves. - 0195-9271 .- 1572-9559. ; 21:11, s. 1831-1835
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Tidskriftsartikel (refereegranskat)abstract
- The boundary problem for Maxwell equations has been solved and computer codes have been written to compute the electrodynamic characteristics of the waveguide structure. The standing wave coefficient's (SWC) dependence on sizes of a n-Si plate, displacement from the waveguide's symmetry plane and electric field amplitude's distribution in these plates have been computed.
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| 29. |
- Tamosiunas, V, et al.
(författare)
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Computation of the reflection coefficient of a triangular semiconductor prism in a rectangular waveguide
- 2000
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Ingår i: International journal of infrared and millimeter waves. - 0195-9271 .- 1572-9559. ; 21:7, s. 1113-1117
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present a method to solve Maxwell's equations that enables to compute waveguide structure containing a semiconductor triangular prism. The numerical study has showed that the triangular prism in the waveguide has a wider frequency band in comparison with a square rod under equal conditions. The reflection coefficient dependences on frequency, prism size and its permittivity have been computed. The algorithm and computer programme have been tested and compared with the numerical results and experimental data of the paper [1] with good agreement.
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| 30. |
- Yakimenko, II, et al.
(författare)
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Symmetry and spin polarization in single and coupled quantum dots
- 2001
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 63:16, s. art. no.-165309
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Tidskriftsartikel (refereegranskat)abstract
- We conducted theoretical investigation into the effect of spontaneous electron spin polarization in single and coupled quantum dots formed by lateral confinement of a high-mobility two-dimensional electron gas in a semiconductor heterostructure. The equilibrium properties of realistic many-electron quantum-dot devices are first studied within the two-dimensional Thomas-Fermi approximation taking into account contributions from the patterned gate, doping, surface states, and mirror charges. In order to explore spin-dependent phenomena, a self-consistent model has been developed using the Kohn-Sham local spin-density formalism. We have tested the contribution of electron correlation in the systems considered and found that it plays a minor role, hence only exchange interactions are included in the model. We investigate the possibilities of manipulating the magnetization (spin polarization) of single and double quantum dots by means of their mutual coupling and symmetry breaking caused by variations in the geometry of the gate.
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| 31. |
- Zozoulenko, Igor, et al.
(författare)
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Magnetoconductance of a few-electron open quantum dot
- 2000
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - 1386-9477 .- 1873-1759. ; 6:1, s. 409-413
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Tidskriftsartikel (refereegranskat)abstract
- Magnetoconductance of a small open lateral dot is studied both theoretically and experimentally for the conditions when the dot contains down to approximately 15 electrons. We confirm the existence of a new regime for open dots in which the transport through the structure occurs through individual eigenstates of the corresponding closed dot. In particular, at low magnetic fields the characteristic features in the conductance are related to the underlying eigenspectrum shells. When the number of modes in the leads is reduced more detailed structures within the shells due to single eigenlevels becomes discernible. At higher fields Landau level condensation is evident as well as the crossing of levels collapsing to the different Landau levels.
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