| 1. |
- 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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| 4. |
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| 5. |
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| 6. |
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| 7. |
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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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| 11. |
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| 12. |
- Fuhrer, Andreas, et al.
(författare)
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Single electron pumping in InAs nanowire double quantum dots
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:5, s. 1-052109
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Tidskriftsartikel (refereegranskat)abstract
- Closely spaced local gate electrodes are used to electrically define a double quantum dot along an InAs nanowire crystal. By applying a periodic pulse sequence to two plunger gate electrodes controlling the double quantum dot charge configuration, the device is operated as a single electron pump. The authors find that within measurement accuracy, the pumping current equals one electron per cycle for frequencies up to 2 MHz, demonstrating the suitability of nanowire based quantum dots for pumping applications.
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| 13. |
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| 14. |
- Fuhrer, Andreas, et al.
(författare)
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Transport studies on nanowire quantum dots
- 2005
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Ingår i: Book of extended abstracts: Niels Bohr Summer School, Copenhagen, Denmark (2005), invited.
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Konferensbidrag (refereegranskat)
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| 15. |
- Hansen, Adam, et al.
(författare)
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Spin relaxation in InAs nanowires studied by tunable weak antilocalization
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. ; 71, s. 1-205328
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Tidskriftsartikel (refereegranskat)abstract
- We report on a low-temperature magnetoconductance study to characterize the electrical and spin transport properties of n-type InAs nanowires grown by chemical beam epitaxy. A gate-controlled crossover from weak localization to weak antilocalization is observed. The measured magnetoconductance data agrees well with theory for one-dimensional quasi-ballistic systems and yields a spin relaxation length which decreases with increasing gate voltage.
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| 16. |
- Johnson, Mats, 1956, et al.
(författare)
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Paediatric acute-onset neuropsychiatric syndrome in children and adolescents: an observational cohort study.
- 2019
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Ingår i: The Lancet. Child & adolescent health. - 2352-4650. ; 3:3, s. 175-180
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Tidskriftsartikel (refereegranskat)abstract
- Paediatric acute-onset neuropsychiatric syndrome (PANS) is a newly defined symptom-based condition that mainly occurs in children and adolescents. Few studies have described the clinical characteristics of the syndrome.We clinically assessed and reviewed the medical histories of children and adolescents (aged 4-14 years) with suspected PANS who were referred to a specialist clinic in Gothenburg, Sweden, by local paediatricians and child psychiatrists. We scored severity of symptoms and impairment retrospectively for the timepoint with the most severe symptoms using the PANS scale.Of 41 patients (37 referred and four visited upon parents' request), 23 (ten girls and 13 boys) met PANS diagnostic criteria. Mean age at PANS onset was 8·5 years (SD 3·37). 11 (48%) patients had a family history of developmental or neuropsychiatric disorders in a first-degree relative and 11 (48%) had a family history of autoimmune or inflammatory diseases in a first-degree relative. 17 (74%) patients had been previously diagnosed with a developmental disorder (n=5) or had symptoms indicative of developmental problems (n=12). A verified or suspected infection was temporally related to PANS onset in all patients; the infection was bacterial in ten (43%) patients (eight had streptococcal infection and two an infection caused by other bacteria) and viral in 13 (57%) patients. All patients had a relapsing-remitting course of illness. The mean PANS scale symptom score was 46 (SD 3·67) and the mean impairment score was 45 (2·74). Antibiotic treatment was reported as beneficial by the parents of 12 (63%) of the 19 children who received antibiotics.Our PANS cohort had severe, acute-onset, complex neuropsychiatric symptoms, a relapsing-remitting symptom course, and possible infectious triggers. Further research into the cause of, and appropriate treatment for, PANS is warranted.Swedish Brain Foundation.
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| 17. |
- Roddaro, Stefano, et al.
(författare)
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Spin States of holes in ge/si nanowire quantum dots.
- 2008
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Ingår i: Physical Review Letters. - 1079-7114. ; 101:18
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Tidskriftsartikel (refereegranskat)abstract
- We investigate tunable hole quantum dots defined by surface gating Ge/Si core-shell nanowire heterostructures. In single level Coulomb-blockade transport measurements at low temperatures spin doublets are found, which become sequentially filled by holes. Magnetotransport measurements allow us to extract a g factor g;{*} approximately 2 close to the value of a free spin-1/2 particle in the case of the smallest dot. In less confined quantum dots smaller g factor values are observed. This indicates a lifting of the expected strong spin-orbit interaction effects in the valence band for holes confined in small enough quantum dots. By comparing the excitation spectrum with the addition spectrum we tentatively identify a hole exchange interaction strength chi approximately 130 mueV.
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| 18. |
- Rydenman, Karin, 1982, et al.
(författare)
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Tonsillectomy reduces the family impact of periodic fever, aphthous stomatitis, pharyngitis and cervical adenitis (PFAPA) syndrome and improves health-related quality of life in affected children
- 2023
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Ingår i: Orphanet Journal of Rare Diseases. - 1750-1172. ; 18:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: Periodic fever, aphthous stomatitis, pharyngitis and cervical adenitis (PFAPA) syndrome is an autoinflammatory disorder that primarily affects young children, and typically gives rise to fever episodes that recur monthly for several years. This study investigated the impact of PFAPA syndrome on the families of affected children, the health-related quality of life (HRQOL) of children with the syndrome, and how these factors were influenced by tonsillectomy. Methods: This prospective cohort study included 24 children with typical PFAPA syndrome that were referred for tonsillectomy, of whom 20 underwent the procedure. The control group consisted of randomly selected children from the general population. Family impact and HRQOL were measured using the standardized, validated questionnaires Pediatric Quality of Life Inventory™ (PedsQL™) Family Impact Module (FIM) and PedsQL™ 4.0 Generic Core Scales (GCS). Parents to children with PFAPA completed the questionnaires before and 6 months after their child underwent tonsillectomy, and HRQOL was measured both between and during PFAPA episodes. The Wilcoxon signed-rank test was used to compare data before and after tonsillectomy in the patient group, while the Mann–Whitney test was used for comparison of the patient and control groups. Results: Before tonsillectomy, children with PFAPA had significantly lower scores than the control group on the PedsQL™ FIM and the PedsQL™ 4.0 GCS during fever episodes. After tonsillectomy, all patients improved with diminished febrile episodes, which resulted in significantly higher scores regarding both family impact and HRQOL at the time of follow-up. HRQOL of in children with PFAPA improved after tonsillectomy even when compared to afebrile intervals before the procedure. The differences between PFAPA patients and controls were eliminated after tonsillectomy. Conclusion: PFAPA syndrome has a profound negative impact on the families of affected children. Tonsillectomy that leads to cessation or reduction of fever episodes eases the impact of the disease on the family. HRQOL in children with PFAPA is low during febrile episodes and similar to healthy controls in between episodes. The improvement of HRQOL in patients with PFAPA after tonsillectomy compared to the afebrile intervals before tonsillectomy highlights that the constantly recurring fevers may affect the children’s well-being even between fever episodes.
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| 19. |
- Sparud Lundin, Carina, 1964, et al.
(författare)
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From uncertainty to gradually managing and awaiting recovery of a periodic condition- a qualitative study of parents´ experiences of PFAPA syndrom
- 2019
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Ingår i: BMC Pediatrics. - : Springer Science and Business Media LLC. - 1471-2431. ; 19:99, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundThe prevalence of periodic fever, aphthous stomatitis, pharyngitis and cervical adenitis (PFAPA) syndrome is unknown. Although an uncommon condition, it is considered to be the most common autoinflammatory disease among children in many parts of the world. The knowledge of the consequences of the recurrent fever episodes for the child and its family are limited. This study explores the experiences of parents regarding the impact of the disease on the child's general well-being, the family's situation and how the family handles the associated challenges.MethodsA qualitative approach was used, applying a modified version of Grounded theory for design, data collection and analysis. Data was collected from two different sources: communication between parents of children with PFAPA in a closed Facebook group and face-to face interviews with one of the parents of children diagnosed with PFAPA (6 mothers and 2 fathers).ResultsParents described a lengthy process of how everyday life becomes affected by their child's recurrent fever episodes. This process is depicted in the following Grounded Theory core category: From uncertainty to gradually managing and awaiting recovery. The categories Uncertainty, Assurance, Gradually managing and Recovery describe the experienced illness trajectory. The illness representation illustrates the experiences/impacts of the periodic condition in the subcategories: Harmlessness-Severity, Disclosure of diagnosis, Impact on daily life and Regularity-Unpredictability. The children's well-being was highly affected by the symptoms during episodes. Parents experienced increased stress with constant fatigue, social constraints of family life and restricted career opportunities. Nevertheless, hope of recovery was constantly present.ConclusionsPFAPA is associated with a considerable burden on the child and the parents in daily life. Obtaining a diagnosis enables parents to move from a state of uncertainty towards a sense of coherence while awaiting recovery. Because of limited general knowledge of the condition and its impact on daily life, health care professionals need to become aware of the parents' efforts to mitigate the consequences of the recurrent episodes for the child and for the family as a whole.
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| 20. |
- Storm, Kristian, et al.
(författare)
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Dual-gate induced InP nanowire diode
- 2011
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Ingår i: Physics of Semiconductors: 30th International Conference on the Physics of Semiconductors. - : AIP. - 1551-7616 .- 0094-243X. ; 1399, s. 279-280
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Konferensbidrag (refereegranskat)abstract
- Semiconductor devices are heavily dependent on dopant incorporation in order to control the electrical properties. In this paper we investigate the possibility of using gates wrapped around a nanowire (NW) channel as a way of tuning the Fermi level position, in certain cases removing the need for dopants and providing a more dynamical way of setting the device properties. InP NW devices with omega gates are fabricated, and a p-n junction is formed in a nominally intrinsic NW channel. In order to further increase the electrostatic control of the channel and other device properties, vertical devices are discussed as a promising way of implementing this type of device.
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| 21. |
- Storm, Kristian, et al.
(författare)
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Gate-Induced Fermi Level Tuning in InP Nanowires at Efficiency Close to the Thermal Limit.
- 2011
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 11, s. 1127-1130
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Tidskriftsartikel (refereegranskat)abstract
- As downscaling of semiconductor devices continues, one or a few randomly placed dopants may dominate the characteristics. Furthermore, due to the large surface-to-volume ratio of one-dimensional devices, the position of the Fermi level is often determined primarily by surface pinning, regardless of doping level. In this work, we investigate the possibility of tuning the Fermi level dynamically with wrap-around gates, instead of statically setting it using the impurity concentration. This is done using Ω-gated metal-oxide-semiconductor field-effect transistors with HfO(2)-capped InP nanowires as channel material. It is found that induced n-type devices exhibit an optimal inverse subthreshold slope of 68 mV/decade. By adjusting the growth and process parameters, it is possible to produce ambipolar devices, in which the Fermi level can be tuned across the entire band gap, making it possible to induce both n-type and p-type conduction.
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| 22. |
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| 23. |
- Weber, Carsten, et al.
(författare)
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Probing Confined Phonon Modes by Transport through a Nanowire Double Quantum Dot
- 2010
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 104:3, s. 1-036801
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Tidskriftsartikel (refereegranskat)abstract
- Strong radial confinement in semiconductor nanowires leads to modified electronic and phononic energy spectra. We analyze the current response to the interplay between quantum confinement effects of the electron and phonon systems in a gate-defined double quantum dot in a semiconductor nanowire. We show that current spectroscopy of inelastic transitions between the two quantum dots can be used as an experimental probe of the confined phonon environment. The resulting discrete peak structure in the measurements is explained by theoretical modeling of the confined phonon mode spectrum, where the piezoelectric coupling is of crucial importance.
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| 24. |
- Xu, Hongqi, et al.
(författare)
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Reflection phase of scattering electrons in a single-channel atomic wire
- 2003
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 68:24
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical study of the phase property of the reflection coefficient of a single-channel quantum system is presented. This reflection phase information is required for a complete characterization of the scattering problem in the system. It is found that the phase of the reflection coefficient of the system shifts abruptly by pi when the reflection probability passes through a zero. It is also found that in certain systems this phase discontinuity can appear even when no zero and no phase discontinuity are present in the transmission coefficient. Possible experiments for the observation of the reflection phase discontinuity are discussed.
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