| 1. |
- Haykal, A., et al.
(författare)
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Decoherence of V-B(-) spin defects in monoisotopic hexagonal boron nitride
- 2022
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Ingår i: Nature Communications. - : Nature Portfolio. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Spin defects in hexagonal boron nitride (hBN) are promising quantum systems for the design of flexible two-dimensional quantum sensing platforms. Here we rely on hBN crystals isotopically enriched with either B-10 or B-11 to investigate the isotope-dependent properties of a spin defect featuring a broadband photoluminescence signal in the near infrared. By analyzing the hyperfine structure of the spin defect while changing the boron isotope, we first confirm that it corresponds to the negatively charged boron-vacancy center (V-B(-)). We then show that its spin coherence properties are slightly improved in B-10-enriched samples. This is supported by numerical simulations employing cluster correlation expansion methods, which reveal the importance of the hyperfine Fermi contact term for calculating the coherence time of point defects in hBN. Using cross-relaxation spectroscopy, we finally identify dark electron spin impurities as an additional source of decoherence. This work provides new insights into the properties of V-B(-) spin defects, which are valuable for the future development of hBN-based quantum sensing foils.
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| 2. |
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| 3. |
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| 4. |
- Csore, A., et al.
(författare)
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Fluorescence spectrum and charge state control of divacancy qubits via illumination at elevated temperatures in 4H silicon carbide
- 2022
-
Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 105:16
-
Tidskriftsartikel (refereegranskat)abstract
- Divacancy in its neutral charge state () in 4H silicon carbide (SiC) is a leading quantum bit (qubit) contender. Owing to the lattice structure of 4H SiC, four different VCVSi configurations can be formed. The ground and the optically accessible excited states of configurations exhibit a high-spin state, and the corresponding optical transition energies are around ≈1.1eV falling in the near-infrared wavelength region. Recently, photoluminescence (PL) quenching has been experimentally observed for all configurations in 4H SiC at cryogenic temperatures. It has been shown that is converted to and it remains in this shelving dark state at cryogenic temperatures until photoexcitation with the threshold energies or above is applied to convert back to . In this study, we demonstrate both in experiments and theory that the threshold energy for reionization is temperature dependent. We carry out density functional theory (DFT) calculations in order to investigate the temperature dependent reionization spectrum, i.e., the spectrum of the process. We find that simultaneous optical reionization and qubit manipulation can be carried out at room temperature with photoexcitation at the typical excitation wavelength used for readout of the divacancy qubits in 4H SiC, in agreement with our experimental data. We also provide the analysis of the PL spectrum of , characteristic for each configuration in 4H SiC, using the Huang-Rhys theory, and find that one configuration in 4H SiC stands out in terms of the strength of coherent emission among the four configurations.
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| 5. |
- Csore, A., et al.
(författare)
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Towards identification of silicon vacancy-related electron paramagnetic resonance centers in 4H-SiC
- 2021
-
Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 104:3
-
Tidskriftsartikel (refereegranskat)abstract
- The negatively charged silicon vacancy (V-Si(-)) in silicon carbide (SiC) is a paramagnetic and optically active defect in hexagonal SiC. The V(Si)(- )defect possesses S = 3/2 spin with long spin coherence time, and it can be optically manipulated even at room temperature. Recently, electron spin resonance signals have been observed besides those associated with the V-Si(- ) defects in the 4H polytype of SiC. The corresponding centers share properties akin to those of the V-Si(- ) defects and thus they may be promising candidates for quantum technology applications. However, the exact origin of the new signals is unknown. In this paper, we report V-1-related pair defect models as possible candidates for the unknown centers. We determine the corresponding electronic structures and magneto-optical properties as obtained by density functional theory calculations. We propose models for the recently observed electron paramagnetic resonance centers, and we predict their optical signals for identification in future experiments.
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| 6. |
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| 7. |
- Son Tien, Nguyen, et al.
(författare)
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Defects at nitrogen site in electron-irradiated AlN
- 2011
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Ingår i: Applied Physics Letters. - : American Institute of Physics. - 0003-6951 .- 1077-3118. ; 98:24, s. 242116-
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Tidskriftsartikel (refereegranskat)abstract
- In high resistance AlN irradiated with 2 MeV electrons, an electron paramagnetic resonance (EPR) spectrum, labeled EI-1, with an electron spin S=1/2 and a clear hyperfine (hf) structure was observed. The hf structure was shown to be due the interaction between the electron spin and the nuclear spins of four (27)A nuclei with the hf splitting varying between similar to 6.0 and similar to 7.2 mT. Comparing the hf data obtained from EPR and ab initio supercell calculations we suggest the EI-1 defect to be the best candidate for the neutral nitrogen vacancy in AlN.
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| 8. |
- Spindlberger, L., et al.
(författare)
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Optical Properties of Vanadium in 4H Silicon Carbide for Quantum Technology
- 2019
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Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- We study the optical properties of tetravalent-vanadium impurities in 4H silicon carbide. Light emission from two crystalline sites is observed at wavelengths of 1.28 and 1.33 mu m, with optical lifetimes of 163 and 43 ns, respectively, which remains stable up to 50 and 20 K, respectively. Moreover, spectrally broad photoluminescence is observed up to room temperature. Group-theory and ab initio density-functional supercell calculations enable unequivocal site assignment and shed light on the spectral features of the defects. Specifically, our numerical simulations indicate that the site assignment is reversed with respect to previous assumptions. Our calculations show that vanadium in silicon carbide has highly favorable properties for the generation of single photons in the telecommunication wavelength regime. Combined with the available electronic and nuclear degrees of freedom, vanadium presents all the ingredients required for a highly efficient spin-photon interface.
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| 9. |
- Szállás, A., et al.
(författare)
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Characterization of the nitrogen split interstitial defect in wurtzite aluminum nitride using density functional theory
- 2014
-
Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 116:11, s. 113702-1-113702-5
-
Tidskriftsartikel (refereegranskat)abstract
- We carried out Heyd-Scuseria-Ernzerhof hybrid density functional theory plane wave supercell calculations in wurtzite aluminum nitride in order to characterize the geometry, formation energies, transition levels, and hyperfine tensors of the nitrogen split interstitial defect. The calculated hyperfine tensors may provide useful fingerprint of this defect for electron paramagnetic resonance measurement.
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| 10. |
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| 11. |
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| 12. |
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| 13. |
- Aiglsperger, Thomas, et al.
(författare)
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Open system Re-Os isotope behavior in platinum-group minerals during laterization?
- 2021
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Ingår i: Minerals. - : MDPI. - 2075-163X. ; 11:10
-
Tidskriftsartikel (refereegranskat)abstract
- In this short communication, we present preliminary data on the Re-Os isotopic systematics of platinum-group minerals (PGM) recovered from different horizons in the Falcondo Ni-laterite in the Dominican Republic. The results show differences in the Os-isotope composition in different populations of PGM: (i) pre-lateritic PGM yield 187 Os/188 Os varying from 0.11973 ± 0.00134 to 0.12215 ± 0.00005 (2σ uncertainty) whereas (ii) lateritic PGM are more radiogenic in terms of 187 Os/188 Os (from 0.12390 ± 0.00001 to 0.12645 ± 0.00005; 2σ uncertainty). We suggest that these differences reflect the opening of the Re-Os system in individual grains of PGM during lateritic weathering. The implications of these results are twofold as they will help to (1) elucidate the small-scale mobility of noble metals in the supergene setting and therefore the possible formation of PGM at these very low temperatures, (2) better refine the Os-isotopic datasets of PGM that are currently being used for defining dynamic models of core–mantle separation, crustal generation, and fundamental plate-tectonic processes such as the opening of oceans.
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| 14. |
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| 15. |
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| 16. |
- Aradi, B., et al.
(författare)
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Ab initio density-functional supercell calculations of hydrogen defects in cubic SiC
- 2001
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 63:245202
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Tidskriftsartikel (refereegranskat)abstract
- Based on ab initio density-functional calculations in supercells of 3C-SiC, the stable configurations of hydrogen and dihydrogen defects have been established. The calculated formation energies are used to give semiquantitative estimates for the concentration of hydrogen in SiC after chemical vapor deposition, low temperature H-plasma anneal, or heat treatment in high temperature hydrogen gas. Vibration frequencies, spin distributions, and occupation levels were also calculated in order to facilitate spectroscopic identification of these defects. (V+nH) complexes are suggested as the origin of some of the signals assigned earlier to pure vacancies. Qualitative extrapolation of our results to hexagonal polytypes explains observed electrical passivation effects of hydrogen.
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| 17. |
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| 18. |
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| 19. |
- Carlsson, Patrick, 1975-, et al.
(författare)
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EPR and ab initio calculation study on the EI4 center in 4H and 6H-SiC
- 2010
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 82:23, s. 235203-
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Tidskriftsartikel (refereegranskat)abstract
- We present new results from electron paramagnetic resonance (EPR) studies of the EI4 EPR center in 4H- and 6H-SiC. The EPR signal of the EI4 center was found to be drastically enhanced in electron-irradiated high-purity semi-insulating materials after annealing at 700-750°C. Strong EPR signals of the EI4 center with minimal interferences from other radiation-induced defects in irradiated high-purity semiinsulating materials allowed our more detailed study of the hyperfine (hf) structures. An additional large-splitting 29Si hf structure and 13C hf lines of the EI4 defect were observed. Comparing the data on the defect formation, the hf interactions and the annealing behavior obtained from EPR experiments and from ab initio supercell calculations of different carbon-vacancy related complexes, we suggest a complex between a carbon vacancy-carbon antisite and a carbon vacancy at the third neighbor site of the antisite in the neutral charge state, (VC-CSiVC)0, as a new defect model for the EI4 center.
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| 20. |
- Castelletto, S., et al.
(författare)
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A silicon carbide room-temperature single-photon source
- 2014
-
Ingår i: Nature Materials. - : Nature Publishing Group. - 1476-1122 .- 1476-4660. ; 13:2, s. 151-156
-
Tidskriftsartikel (refereegranskat)abstract
- Over the past few years, single-photon generation has been realized in numerous systems: single molecules(1), quantum dots(2-4), diamond colour centres5 and others(6). The generation and detection of single photons play a central role in the experimental foundation of quantum mechanics(7) and measurement theory(8). An efficient and high-quality single-photon source is needed to implement quantum key distribution, quantum repeaters and photonic quantum information processing(9). Here we report the identification and formation of ultrabright, room-temperature, photostable single-photon sources in a device-friendly material, silicon carbide (SiC). The source is composed of an intrinsic defect, known as the carbon antisite-vacancy pair, created by carefully optimized electron irradiation and annealing of ultrapure SiC. An extreme brightness (2 x 10(6) counts s(-1)) resulting from polarization rules and a high quantum efficiency is obtained in the bulk without resorting to the use of a cavity or plasmonic structure. This may benefit future integrated quantum photonic devices(9).
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| 21. |
- Dahl, Niklas, et al.
(författare)
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Missense mutations in the human glutathione synthetase gene result in severe metabolic acidosis, 5-oxoprolinuria, hemolytic anemia and neurological dysfunction
- 1997
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Ingår i: Human Molecular Genetics. - : Oxford University Press (OUP). - 0964-6906 .- 1460-2083. ; 6:7, s. 1147-1152
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Tidskriftsartikel (refereegranskat)abstract
- Severe glutathione synthetase (GS) deficiency is a rare genetic disorder with neonatal onset. The enzymatic block of the gamma-glutamyl cycle leads to a generalized glutathione deficiency. Clinically affected patients present with severe metabolic acidosis, 5-oxoprolinuria, increased rate of hemolysis and defective function of the central nervous system. The disorder is inherited in an autosomal recessive mode and, until recently, the molecular basis has remained unknown. We have sequenced 18 GS alleles associated with enzyme deficiency and we detected missense mutations by direct sequencing of cDNAs and genomic DNA. In total, 13 different mutations were identified. Four patients were found to be compound heterozygotes and two individuals were apparently homozygous. Reduced enzymatic activities were demonstrated in recombinant protein expressed from cDNAs in four cases with different missense mutations. The results from biochemical analysis of patient specimens, supported by the properties of the expressed mutant proteins, indicate that a residual activity is present in affected individuals. Our results suggest that complete loss of function of both GS alleles is probably lethal. It is postulated that missense mutations will account for the phenotype in the majority of patients with severe GS deficiency.
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| 22. |
- Gali, A., et al.
(författare)
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Ab initio supercell calculations on aluminum-related defects in SiC
- 2007
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:4
-
Tidskriftsartikel (refereegranskat)abstract
- Ab initio supercell calculations of the binding energies predict complex formation between aluminum and carbon interstitials in SiC. In high-energy implanted SiC aluminum acceptor can form very stable complexes with two carbon interstitials. We also show that carbon vacancy can be attached to shallow aluminum acceptor. All of these defects produce deep levels in the band gap. The possible relation of these defects to the recently found aluminum-related deep-level transient spectroscopy centers is discussed. © 2007 The American Physical Society.
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| 23. |
- Gali, A, et al.
(författare)
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Activation of shallow boron acceptor in CB coimplanted silicon carbide : A theoretical study
- 2005
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 86:10, s. 102108-
-
Tidskriftsartikel (refereegranskat)abstract
- Ab initio supercell calculations have been carried out to investigate the complexes of boron acceptors with carbon self-interstitials in cubic silicon carbide. Based on the calculated binding energies, the complex formation of carbon interstitials with shallow boron acceptor and boron interstitial is energetically favored in silicon carbide. These bistable boron defects possess deep, negative- U occupation levels in the band gap. The theoretical results can explain the observed activation rates in carbon-boron coimplantation experiments. © 2005 American Institute of Physics.
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| 24. |
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| 25. |
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| 26. |
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| 27. |
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| 28. |
- Goodman, Daisy, et al.
(författare)
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Explanation and elaboration of the SQUIRE (Standards for Quality Improvement Reporting Excellence) Guidelines, V.2.0 : Examples of SQUIRE elements in the healthcare improvement literature
- 2016
-
Ingår i: BMJ Quality and Safety. - : BMJ. - 2044-5415 .- 2044-5423. ; 25:12
-
Tidskriftsartikel (refereegranskat)abstract
- Since its publication in 2008, SQUIRE (Standards for Quality Improvement Reporting Excellence) has contributed to the completeness and transparency of reporting of quality improvement work, providing guidance to authors and reviewers of reports on healthcare improvement work. In the interim, enormous growth has occurred in understanding factors that influence the success, and failure, of healthcare improvement efforts. Progress has been particularly strong in three areas: the understanding of the theoretical basis for improvement work; the impact of contextual factors on outcomes; and the development of methodologies for studying improvement work. Consequently, there is now a need to revise the original publication guidelines. To reflect the breadth of knowledge and experience in the field, we solicited input from a wide variety of authors, editors and improvement professionals during the guideline revision process. This Explanation and Elaboration document (E&E) is a companion to the revised SQUIRE guidelines, SQUIRE 2.0. The product of collaboration by an international and interprofessional group of authors, this document provides examples from the published literature, and an explanation of how each reflects the intent of a specific item in SQUIRE. The purpose of the guidelines is to assist authors in writing clearly, precisely and completely about systematic efforts to improve the quality, safety and value of healthcare services. Authors can explore the SQUIRE statement, this E&E and related documents in detail at http://www.squire-statement.org.
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| 29. |
- Green, B. L., et al.
(författare)
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All-optical hyperpolarization of electron and nuclear spins in diamond
- 2017
-
Ingår i: Physical Review B. - College Park : American Physical Society. - 2469-9950 .- 2469-9969. ; 96:5
-
Tidskriftsartikel (refereegranskat)abstract
- Low thermal polarization of nuclear spins is a primary sensitivity limitation for nuclear magnetic resonance. Here we demonstrate optically pumped (microwave-free) nuclear spin polarization of C-13 and N-15 in N-15-doped diamond. (15)Npolarization enhancements up to- 2000 above thermal equilibrium are observed in the paramagnetic system Ns(0). Nuclear spin polarization is shown to diffuse to bulk C-13 with NMR enhancements of -200 at room temperature and -500 at 240 K, enabling a route to microwave-free high-sensitivity NMR study of biological samples in ambient conditions.
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| 30. |
- Gällström, Andreas, et al.
(författare)
-
A defect center for quantum computing : Mo in SiC
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The electronic structure and vibrational properties of molybdenum (Mo) in SiC are analyzed and investigated in detail. Mo is considered as occupying the silicon-carbon divacancy in the so-called asymmetric split vacancy (ASV) configuration. Group-theoretical considerations within this model are used to explain the experimental results (optical properties and behavior in magnetic field). The vibrational properties of the defect are studied using simple the “defect molecule” model with parameters determined phenomenologically from the experimental data. The position of Mo in the ASV configuration deduced from this model is shown to be in good agreement with the earlier reported data from ab initio supercell calculations. The usefulness of molybdenum in SiC in quantum computing is investigated, and it shown that Mo is a highly promising candidate for quantum computing.
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| 31. |
- Gällström, Andreas, et al.
(författare)
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Optical properties and Zeeman spectroscopy of niobium in silicon carbide
- 2015
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 92:7, s. 1-14
-
Tidskriftsartikel (refereegranskat)abstract
- The optical signature of niobium in the low-temperature photoluminescence spectra of three common polytypes of SiC (4H, 6H, and 15R) is observed and confirms the previously suggested concept that Nb occupies preferably the Si-C divacancy with both Si and C at hexagonal sites. Using this concept we propose a model considering a Nb-bound exciton, the recombination of which is responsible for the observed luminescence. The exciton energy is estimated using first-principles calculation and the result is in very good agreement with the experimentally observed photon energy in 4H SiC at low temperature. The appearance of six Nb-related lines in the spectra of the hexagonal 4H and 6H polytypes at higher temperatures is tentatively explained on the grounds of the proposed model and the concept that the Nb center can exist in both C1h and C3v symmetries. The Zeeman splitting of the photoluminescence lines is also recorded in two different experimental geometries and the results are compared with theory based on phenomenological Hamiltonians. Our results show that Nb occupying the divacancy at the hexagonal site in the studied SiC polytypes behaves like a deep acceptor.
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| 32. |
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| 33. |
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| 34. |
- Ivády, Viktor, et al.
(författare)
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Role of screening in the density functional applied to transition-metal defects in semiconductors
- 2013
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 87:20
-
Tidskriftsartikel (refereegranskat)abstract
- We study selected transition-metal-related point defects in silicon and silicon carbide semiconductors by a range-separated hybrid density functional (HSE06). We find that HSE06 does not fulfill the generalized Koopmans' theorem for every defect, which is due to the self-interaction error in the functional in such cases. Restoring the so-called generalized Koopmans' condition with a simple correction in the functional can eliminate this error and brings the calculated charge transition levels remarkably close to the experimental data as well as to the calculated quasiparticle levels from many-body perturbation theory.
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| 35. |
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| 36. |
- Nguyen, Son Tien, 1953-, et al.
(författare)
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Divacancy in 4H-SiC
- 2006
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 96:5, s. 055501-1-055501-4
-
Tidskriftsartikel (refereegranskat)abstract
- Electron paramagnetic resonance and ab initio supercell calculations suggest that the P6/P7 centers, which were previously assigned to the photoexcited triplet states of the carbon vacancy-antisite pairs in the double positive charge state, are related to the triplet ground states of the neutral divacancy. The spin density is found to be located mainly on three nearest C neighbors of the silicon vacancy, whereas it is negligible on the nearest Si neighbors of the carbon vacancy.
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| 37. |
- Nguyen, Tien Son, et al.
(författare)
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Identification of divacancies in 4H-SiC
- 2006
-
Ingår i: Physica B: Condensed Matter, Vols. 376-377. - : Elsevier BV. ; , s. 334-337
-
Konferensbidrag (refereegranskat)abstract
- The P6/P7 centers in 4H-SiC were studied by electron paramagnetic resonance (EPR) and ab initio supercell calculations. The hyperfine coupling constants of C and Si neighbors obtained by EPR are in good agreement with the calculated values for the neutral divacancy, VCVsi0. Our results suggest that the P6/P7 centers, which were previously assigned to the photo-excited triplet states of the carbon vacancy-carbon antisite pairs in the double positive charge state (VCCsi2+), are related to the triplet ground states of the C-3v/C-1h si configurations of VCVsi0 (c) 2006 Elsevier B.V. All rights reserved.
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| 38. |
- Steinmann, S., et al.
(författare)
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Hsp90 inhibition by AUY922 as an effective treatment strategy against myxoid liposarcoma
- 2015
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Ingår i: Cancer Letters. - : Elsevier BV. - 0304-3835. ; 367:2, s. 147-156
-
Tidskriftsartikel (refereegranskat)abstract
- Liposarcoma is one of the most common soft tissue sarcomas in adults. Recognized histological subtypes include well differentiated/dedifferentiated liposarcoma (WD/DDLS), myxoid liposarcoma (MLS) and pleomorphic liposarcoma. Currently, there are no proper subtype-specific treatments due to the genetic, histological and clinical heterogeneity of the liposarcoma subentities. In the past decade, the rising understanding of the various genetic and molecular aberrations in liposarcoma led to the development of novel alternative therapeutic strategies. One such therapy is the inhibition of the heat shock protein 90 (Hsp90) which is overexpressed in liposarcomas. In this study, we dissect the functional role of a novel potent Hsp90 inhibitor NVP-AUY922 (AUY922) in different cell lines of myxoid (ML5402, MLS1765) and undifferentiated (SW872) liposarcomas. We show that compared with 17-AAG treatment, lower concentrations of AUY922 achieve markedly cytotoxic effects on tumor cell viability. Combination treatment of AUY922 (20 nM) with Doxorubicin (300 nM) yielded a further reduction in cell viability in comparison to Doxorubicin alone. In vivo, we document an inhibition of tumor growth after AUY922 treatment. Further analyses revealed that Hsp90-inhibition induces apoptotic cell death and cell cycle arrest. In addition, we report striking perturbations of subtype-specific pattern in Raf/MEK/ERK and PI3K signaling after AUY922 application. In conclusion, our results provide evidence that Hsp90-inhibition by AUY922 may be a promising alternative therapeutic strategy for myxoid liposarcoma patients. (C) 2015 Published by Elsevier Ireland Ltd.
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| 39. |
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| 40. |
- Szasz, K., et al.
(författare)
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First principles investigation of divacancy in SiC polytypes for solid state qubit application
- 2014
-
Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2. - Stafa-Zurich, Switzerland : Trans Tech Publications. - 9783038350101 ; , s. 499-502
-
Konferensbidrag (refereegranskat)abstract
- We calculated the hyperfine structure and the zero-field splitting parameters of divacancies in 3C, 4H and 6H SiC in the ground state and in the excited state for 4H SiC within the framework of density functional theory. Besides that our calculations provide identification of the defect in different polytypes, we can find some carbon atoms next to the divacancy that of the spin polarizations are similar in the ground and excited states. This coherent nuclear spin polarization phenomenon can be the base to utilize 13C spins as quantum memory.
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| 41. |
- Szasz, K., et al.
(författare)
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Theoretical and electron paramagnetic resonance studies of hyperfine interaction in nitrogen doped 4H and 6H SiC
- 2014
-
Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 115:7, s. 073705-
-
Tidskriftsartikel (refereegranskat)abstract
- Motivated by recent experimental findings on the hyperfine signal of nitrogen donor (N-C) in 4H and 6H SiC, we calculate the hyperfine tensors within the framework of density functional theory. We find that there is negligible hyperfine coupling with Si-29 isotopes when NC resides at h site both in 4H and 6H SiC. We observe measurable hyperfine coupling to a single Si-29 at k site in 4H SiC and k(1) site in 6H SiC. Our calculations unravel that such Si-29 hyperfine coupling does not occur at k(2) site in 6H SiC. Our findings are well corroborated by our new electron paramagnetic resonance studies in nitrogen doped 6H SiC.
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| 42. |
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| 43. |
- Trinh, Xuan Thang, et al.
(författare)
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Negative-U carbon vacancy in 4H-SiC : Assessment of charge correction schemes and identification of the negative carbon vacancy at the quasicubic site
- 2013
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 88:23, s. 235209-1-235209-13
-
Tidskriftsartikel (refereegranskat)abstract
- The carbon vacancy (VC) has been suggested by different studies to be involved in the Z1/Z2 defect-a carrier lifetime killer in SiC. However, the correlation between the Z1/Z2 deep level with VC is not possible since only the negative carbon vacancy (V−C) at the hexagonal site, V−C(h), with unclear negative-U behaviors was identified by electron paramagnetic resonance (EPR). Using freestanding n-type 4H-SiC epilayers irradiated with low energy (250 keV) electrons at room temperature to introduce mainly VC and defects in the C sublattice, we observed the strong EPR signals of V−C(h) and another S = 1/2 center. Electron paramagnetic resonance experiments show a negative-U behavior of the two centers and their similar symmetry lowering from C3v to C1h at low temperatures. Comparing the 29Si and 13C ligand hyperfine constants observed by EPR and first principles calculations, the new center is identified as V−C(k). The negative-U behavior is further confirmed by large scale density functional theory supercell calculations using different charge correction schemes. The results support the identification of the lifetime limiting Z1/Z2 defect to be related to acceptor states of the carbon vacancy.
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| 44. |
- Umeda, T, et al.
(författare)
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Dicarbon antisite defect in n-type 4H-SiC
- 2009
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Ingår i: PHYSICAL REVIEW B. - 1098-0121. ; 79:11, s. 115211-
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Tidskriftsartikel (refereegranskat)abstract
- We identify the negatively charged dicarbon antisite defect (C-2 core at silicon site) in electron-irradiated n-type 4H-SiC by means of combined electron paramagnetic resonance (EPR) measurements and first-principles calculations. The HEI5 and HEI6 EPR centers (S=1/2; C-1h symmetry) are associated with cubic and hexagonal dicarbon antisite defects, respectively. This assignment is based on a comparison of the measured and calculated hyperfine tensors of C-13 and Si-29 atoms as far as the second neighborhood around the defects. Theoretically, the dicarbon antisites are stable in a single negative charge state under a wide range of n-type samples. We found that the defects can be created under a wide range of irradiation conditions, and our measurements strongly suggest the existence of carbon antisite defects in the as-grown samples. Annealing studies revealed several atomistic processes such as recombination of carbon interstitials with vacancies and formation of carbon aggregates. These processes were activated at about 1000 degrees C, and as theoretically predicted, the dicarbon antisite is much more stable than the dicarbon interstitial defect (C-2 core at carbon site). The measured activation temperature is consistent with the temperature range for forming various carbon aggregate-related photoluminescence centers.
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| 45. |
- Umeda, T., et al.
(författare)
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EPR and theoretical studies of positively charged carbon vacancy in 4H-SiC
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 70:23
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Tidskriftsartikel (refereegranskat)abstract
- The carbon vacancy is a dominant defect in 4H-SiC, and the "E15" electron-paramagnetic-resonance (EPR) spectrum originates from positively charged carbon vacancies (VC+) at quasicubic sites. The observed state for EI5, however, has been attributed to a motional-averaged state with the C3v symmetry, and its true atomic structure has not been revealed so far. We here report low temperature (
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| 46. |
- Widmann, Matthias, et al.
(författare)
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Electrical Charge State Manipulation of Single Silicon Vacancies in a Silicon Carbide Quantum Optoelectronic Device
- 2019
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Ingår i: Nano letters (Print). - : AMER CHEMICAL SOC. - 1530-6984 .- 1530-6992. ; 19:10, s. 7173-7180
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Tidskriftsartikel (refereegranskat)abstract
- Color centers with long-lived spins are established platforms for quantum sensing and quantum information applications. Color centers exist in different charge states, each of them with distinct optical and spin properties. Application to quantum technology requires the capability to access and stabilize charge states for each specific task. Here, we investigate charge state manipulation of individual silicon vacancies in silicon carbide, a system which has recently shown a unique combination of long spin coherence time and ultrastable spin-selective optical transitions. In particular, we demonstrate charge state switching through the bias applied to the color center in an integrated silicon carbide optoelectronic device. We show that the electronic environment defined by the doping profile and the distribution of other defects in the device plays a key role for charge state control. Our experimental results and numerical modeling evidence that control of these complex interactions can, under certain conditions, enhance the photon emission rate. These findings open the way for deterministic control over the charge state of spin-active color centers for quantum technology and provide novel techniques for monitoring doping profiles and voltage sensing in microscopic devices.
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| 47. |
- Wirtitsch, D., et al.
(författare)
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Exploiting ionization dynamics in the nitrogen vacancy center for rapid, high-contrast spin, and charge state initialization
- 2023
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Ingår i: Physical Review Research. - : AMER PHYSICAL SOC. - 2643-1564. ; 5:1
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Tidskriftsartikel (refereegranskat)abstract
- We propose and experimentally demonstrate a method to strongly increase the sensitivity of spin measure-ments on nitrogen vacancy (NV) centers in diamond, which can be readily implemented in existing quantum sensing experiments. While charge state transitions of this defect are generally considered a parasitic effect to be avoided, we show here that these can be used to significantly increase the NV centers spin contrast, a key quantity for high-sensitivity magnetometry and high-fidelity state readout. The protocol consists of a two-step procedure, in which the charge state of the defect is first purified by a strong laser pulse, followed by weak illumination to obtain high spin polarization. We observe a relative improvement of the readout contrast by 17% and infer a reduction of the initialization error of more than 50%. The contrast enhancement is accompanied by a beneficial increase of the readout signal. For long sequence durations, typically encountered in high-resolution magnetometry, a measurement speedup by a factor of >1.5 is extracted, and we find that the technique is beneficial for sequences of any duration. Additionally, our findings give detailed insight into the charge and spin polarization dynamics of the NV center and provide actionable insights for direct optical, spin-to-charge, and electrical readout of solid-state spin centers.
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