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- Cinthio, Magnus, et al.
(författare)
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Instruktioner för laborationsrapportskrivande
- 2008
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Ingår i: [Host publication title missing].
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Konferensbidrag (refereegranskat)abstract
- I denna undersökning studeras hur laborations- rapporter vid LTH motiveras som pedagogiskt moment, hur skrivinstruktionerna är relaterade till lärandemomentet, och om detta kan förbättras. Det visar sig att de flesta instruktioner endast mycket kortfattat motiverar varför laborationsrapporter skrivs även om kursansvariga har ambitiösa mål med momentet. I skrivinstruktionerna finns ofta fler dispositions- och formaliainstruktioner än sådana som syftar till reflektion, till att förbättra skrivandet eller som uppmuntrar till vetenskapligt tänkande. Ett intressant angreppssätt, LabWrite, används vid North Carolina State University at Rayleigh, USA, där laboration och rapport används som ett sätt för studenten att också lära sig ett vetenskapligt förhållningssätt. LabWrite är intressant, men som första steg anser vi att instruktionen kan göras tydligare. Ett förslag är att dela upp den i tre distinkta delar; instruktioner som syftar till kritiskt tänkande, instruktioner om disposition och layout och slutligen instruktioner av teknisk karaktär.
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| 2. |
- Fasth, Carina, et al.
(författare)
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Direct Measurement of the Spin-Orbit Interaction in a Two-Electron InAs Nanowire Quantum Dot
- 2007
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Ingår i: Physical Review Letters. - 1079-7114. ; 98, s. 1-266801
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate control of the electron number down to the last electron in tunable few-electron quantum dots defined in catalytically grown InAs nanowires. Using low temperature transport spectroscopy in the Coulomb blockade regime, we propose a method to directly determine the magnitude of the spin-orbit interaction in a two-electron artificial atom with strong spin-orbit coupling. Because of a large effective g factor |g*|=8±1, the transition from a singlet S to a triplet T+ ground state with increasing magnetic field is dominated by the Zeeman energy rather than by orbital effects. We find that the spin-orbit coupling mixes the T+ and S states and thus induces an avoided crossing with magnitude ΔSO=0.25±0.05 meV. This allows us to calculate the spin-orbit length λSO≈127 nm in such systems using a simple model.
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| 3. |
- Fasth, Carina, et al.
(författare)
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Effects of breaking current conservation on the phase properties of two-terminal quantum systems
- 2003
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Ingår i: Physica E: Low-Dimensional Systems and Nanostructures. - 1386-9477. ; 17:1-4, s. 579-583
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Tidskriftsartikel (refereegranskat)abstract
- We study the reflection and transmission phase properties of two-terminal quantum structures coupled to a third lead. The systems are effectively three-terminal and current conservation is broken with regard to the original two-terminal systems. Two structures, a waveguide with an attached stub quantum dot and a waveguide with an inline, double-barrier confined quantum dot, are considered. The transmission and reflection phase properties are calculated for these systems with different couplings to the third lead. The results show that the discontinuous phase shifts seen in the current-conserved two-terminal systems are removed when the third lead is attached. However, as long as the coupling between the quantum systems and the additional lead is weak, sharp but continuous phase drops within narrow energy ranges can still be clearly identified.
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| 8. |
- Fasth, Carina
(författare)
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Theoretical Studies of Electron Transport in Quantum Dot Structures
- 2004
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We calculate the phase property of the reflection coefficient in two-terminal structures using a lattice tight-binding model. It is seen that, provided that there exist two coherent reflection paths, the reflection probability can be zero for certain electron energies. At these energies, the phase of the reflection coefficient shift abruptly by $pi$. Next, we study the reflection and transmission phase properties of two-terminal structures coupled to a third lead. The systems are effectivley three-terminal and current conservation is broken with regard to the original two-terminal systems. Two structures, a waveguide with an attached stub quantum dot and a waveguide with an inline, double-barrier confined quantum dot, are considered. The transmission and reflection phase properties are calculated for these systems with different couplings to the third lead. The results show that the discontinuous phase shifts seen in the current-conserved two-terminal systems are removed when the third lead is attached. However, as long as the coupling between the quantum systems and the additional lead is weak, sharp but continuous phase drops within narrow energy ranges can still be clearly identified. Finally, transport through a di-atomic asymmetric artificial molecule (double quantum dot) in the non-linear response regime is studied by means of the same model, but now including self-consistent electron-electron interactions in the Hartree-Fock approximation. This approach takes into account the delocalized quantum states of the two coupled quantum dots. The current-voltage characteristic is found to be strongly non-linear and strikingly different for opposite bias polarities, indicating a possibility for the structure to be utilized as a current rectifier. We also find that it is possible to obtain spin-polarized currents. The observed features are found to result from an interplay between Pauli spin blockade and transmission through molecular states, the localizations of which are sensitive to the applied bias.
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| 9. |
- Fasth, Carina
(författare)
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Transport Studies of Local-Gate Defined Quantum Dots in Nanowires
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on electrical transport in semiconductor InAs nanowires grown by chemical beam epitaxy. Initially, transport length scales of homogeneous InAs n-type nanowires are characterized by low-temperature magnetoconductance measurements. The measurements show phase-coherent conductivity corrections. By fitting the data, we find the nanowire mean-free path to be 50 nm and the phase-coherence and spin scattering lengths to be ~200nm. The spin scattering is attributed to spin-orbit coupling which is strong in narrow-bandgap semi-conductors such as InAs. The major part of the thesis work concerns quantum dots in InAs nanowires. We demonstrate a technique where quantum dots are electrostatically induced along the nanowire by depletion of the electronic gas from nano-scale local gate electrodes. The major advantage of this method is the tunability of the devices as the charge states of induced quantum dots and the couplings between them are controlled by external voltages. Using low temperature transport spectroscopy on a single dot in the few-electron Coulomb blockade regime we determine an effective g^*-factor in these dots of 8pm 1. In a two-electron dot we observe a Zeeman-driven ground state transition from singlet S to triplet T^+, which is characterized by an anti-crossing. This is attributed to S-T^+ mixing by spin-orbit coupling and a spin-orbit scattering length of ~130 nm for confined electrons can be extracted from the magnitude of the anti-crossing. In gate-defined few-electron double quantum dots, we observe a leakage current at the spin-blockaded (1,1) to (0,2) charge transition, which also originates in singlet-triplet mixing. The leakage current is strongly dependent of external magnetic field and of level detuning, however, this dependence changes drastically when the interdot coupling is varied. From a device point of view, the controllable charging of a (many-electron) double dot is utilized to demonstrate the operation of a single electron pump. Within measurement accuracy the pumping current equals one electron per cycle for frequencies up to 2 MHz. We also consider Ge/Si core-shell heterostructure nanowires wherein the band offsets result in a hole channel in the wire core. Using local top-gates, we demonstrate fully tunable gate-induced single and double quantum dots. Low-temperature transport measurements were used to extract the hole $g$-factor. The data indicate a strongly anisotropic g-factor with |g_parallel|=0.6 and |g_perp|<0.12.
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| 10. |
- Fasth, Carina, et al.
(författare)
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Tunable double quantum dots in InAs nanowires defined by local gate electrodes
- 2005
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 5:7, s. 1487-1490
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Tidskriftsartikel (refereegranskat)abstract
- We report on low-temperature transport measurements on single and double quantum dots defined using local gates to electrostatically deplete InAs nanowires grown by chemical beam epitaxy. This technique allows us to define multiple quantum dots along a semiconducting nanowire and tune the coupling between them.
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