| 1. |
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| 2. |
- Aad, G., et al.
(författare)
-
Combination of searches for invisible decays of the Higgs boson using 139 fb−1 of proton-proton collision data at √s=13 TeV collected with the ATLAS experiment
- 2023
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 842
-
Tidskriftsartikel (refereegranskat)abstract
- Many extensions of the Standard Model predict the production of dark matter particles at the LHC. Sufficiently light dark matter particles may be produced in decays of the Higgs boson that would appear invisible to the detector. This Letter presents a statistical combination of searches for H→invisible decays where multiple production modes of the Standard Model Higgs boson are considered. These searches are performed with the ATLAS detector using 139 fb−1 of proton–proton collisions at a centre–of–mass energy of at the LHC. In combination with the results at √s=7TeV and 8TeV, an upper limit on the H→invisible branching ratio of 0.107 (0.077) at the 95% confidence level is observed (expected). These results are also interpreted in the context of models where the 125 GeV Higgs boson acts as a portal to dark matter, and limits are set on the scattering cross-section of weakly interacting massive particles and nucleons.
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| 3. |
- Aad, G., et al.
(författare)
-
Constraints on the Higgs boson self-coupling from single- and double-Higgs production with the ATLAS detector using pp collisions at √s=13 TeV
- 2023
-
Ingår i: Physics Letters B. - : Elsevier B.V.. - 0370-2693 .- 1873-2445. ; 843
-
Tidskriftsartikel (refereegranskat)abstract
- Constraints on the Higgs boson self-coupling are set by combining double-Higgs boson analyses in the b¯bb¯b, b¯bτ +τ − and b¯bγγ decay channels with single-Higgs boson analyses targeting the γγ , Z Z∗, W W ∗, τ +τ − and b¯b decay channels. The data used in these analyses were recorded by the ATLAS detector at the LHC in proton–proton collisions at √s = 13 TeV and correspond to an integrated luminosity of 126–139 fb−1. The combination of the double-Higgs analyses sets an upper limit of μH H < 2.4 at 95% confidence level on the double-Higgs production cross-section normalised to its Standard Model prediction. Combining the single-Higgs and double-Higgs analyses, with the assumption that new physics affects only the Higgs boson self-coupling (λHHH ), values outside the interval −0.4 < κλ = (λHHH /λ ) < 6.3 are excluded at 95% confidence level. The combined single-Higgs and double-Higgs analyses provide results with fewer assumptions, by adding in the fit more coupling modifiers introduced to account for the Higgs boson interactions with the other Standard Model particles. In this relaxed scenario, the constraint becomes −1.4 < κλ < 6.1 at 95% CL
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| 4. |
- Aad, G., et al.
(författare)
-
Measurement of the polarisation of W bosons produced in top-quark decays using dilepton events at √s=13 TeV with the ATLAS experiment
- 2023
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 843
-
Tidskriftsartikel (refereegranskat)abstract
- measurement of the polarisation of W bosons produced in top-quark decays is presented, using proton–proton collision data at a centre-of-mass energy of √s=13 TeV. The data were collected by the ATLAS detector at the Large Hadron Collider and correspond to an integrated luminosity of 139 fb−1. The measurement is performed selecting events decaying into final states with two charged leptons (electrons or muons) and at least two b-tagged jets. The polarisation is extracted from the differential cross-section distribution of the cosθ* variable, where θ* is the angle between the momentum direction of the charged lepton from the W boson decay and the reversed momentum direction of the b-quark from the top-quark decay, both calculated in the W boson rest frame. Parton-level results, corrected for the detector acceptance and resolution, are presented for the cosθ* angle. The measured fractions of longitudinal, left- and right-handed polarisation states are found to be f0=0.684±0.005(stat.)±0.014(syst.), fL=0.318±0.003(stat.)±0.008(syst.) and fR=−0.002±0.002(stat.)±0.014(syst.), in agreement with the Standard Model prediction.
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| 5. |
- Aad, G., et al.
(författare)
-
Measurement of the t¯t¯ cross section and its ratio to the Z production cross section using pp collisions at √s=13.6 TeV with the ATLAS detector
- 2024
-
Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 848
-
Tidskriftsartikel (refereegranskat)abstract
- The inclusive top-quark-pair production cross section ???̄ and its ratio to the ?-boson production cross section have been measured in proton–proton collisions at √? = 13.6 TeV, using 29 fb−1 of data collected in 2022 with the ATLAS experiment at the Large Hadron Collider. Using events with an opposite-charge electron-muon pair and ?-tagged jets, and assuming Standard Model decays, the top-quark-pair production cross section is measured to be ???̄ = 850± 3(stat.) ± 18(syst.) ± 20(lumi.) pb. The ratio of the ??̄ and the ?-boson production cross sections is also measured, where the ?-boson contribution is determined for inclusive ?+?− and ?+?− events in a fiducial phase space. The relative uncertainty on the ratio is reduced compared to the ??̄ cross section, thanks to the cancellation of several systematic uncertainties. The result for the ratio, ???̄∕? = 1.145 ± 0.003(stat.) ± 0.021(syst.)±0.002(lumi.) is consistent with the Standard Model prediction using the PDF4LHC21 PDF set.
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| 6. |
- Aad, G., et al.
(författare)
-
Search for exclusive Higgs and Z boson decays to ωγ and Higgs boson decays to K⁎γ with the ATLAS detector
- 2023
-
Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 847
-
Tidskriftsartikel (refereegranskat)abstract
- Searches for the exclusive decays of the Higgs boson to an ? meson and a photon or a ?* meson and a photon can probe flavour-conserving and flavour-violating Higgs boson couplings to light quarks, respectively. Searches for these decays, along with the analogous ? boson decay to an ? meson and a photon, are performed with a ?? collision data sample corresponding to integrated luminosities of up to 134 fb−1 collected at √? = 13 TeV with the ATLAS detector at the CERN Large Hadron Collider. The obtained 95% confidence-level upper limits on the respective branching fractions are (? → ??) < 5.5 × 10−4, (? → ?*?) < 2.2 × 10−4 and (? → ??) < 3.9 × 10−6. The limits for ? → ?? and ? → ?? are 370 times and 140 times the Standard Model expected values, respectively. The result for ? → ?? corresponds to a two-orders-of-magnitude improvement over the limit obtained by the DELPHI experiment at LEP.
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| 7. |
- Aad, G., et al.
(författare)
-
Search for flavour-changing neutral-current couplings between the top quark and the photon with the ATLAS detector at √s=13 TeV
- 2023
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 842
-
Tidskriftsartikel (refereegranskat)abstract
- This letter documents a search for flavour-changing neutral currents (FCNCs), which are strongly suppressed in the Standard Model, in events with a photon and a top quark with the ATLAS detector. The analysis uses data collected in pp collisions at √s = 13 TeV during Run 2 of the LHC, corresponding to an integrated luminosity of 139 fb−1. Both FCNC top-quark production and decay are considered. The final state consists of a charged lepton, missing transverse momentum, a b-tagged jet, one high-momentum photon and possibly additional jets. A multiclass deep neural network is used to classify events either as signal in one of the two categories, FCNC production or decay, or as background. No significant excess of events over the background prediction is observed and 95% CL upper limits are placed on the strength of left- and right-handed FCNC interactions. The 95% CL bounds on the branching fractions for the FCNC top-quark decays, estimated (expected) from both top-quark production and decay, are B(t → uγ ) < 0.85 (0.88) × 10−5 and B(t → cγ ) < 4.2 (3.40) × 10−5 for a left-handed tqγ coupling, and B(t → uγ ) < 1.2 (1.20)×10−5 and B(t → cγ ) < 4.5 (3.70)×10−5 for a right-handed coupling.
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| 8. |
- Aad, G., et al.
(författare)
-
Search for heavy long-lived multi-charged particles in the full LHC Run 2 pp collision data at √s=13 TeV using the ATLAS detector
- 2023
-
Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 847
-
Tidskriftsartikel (refereegranskat)abstract
- A search for heavy long-lived multi-charged particles is performed using the ATLAS detector at the LHC. Data collected in 2015-2018 at √s = 13 TeV from pp collisions corresponding to an integrated luminosity of 139 fb−1 are examined. Particles producing anomalously high ionization, consistent with long-lived spin-½ massive particles with electric charges from |q| = 2e to |q| = 7e are searched for. No statistically significant evidence of such particles is observed, and 95% confidence level cross-section upper limits are calculated and interpreted as the lower mass limits for a Drell-Yan plus photon-fusion production mode. The least stringent limit, 1060 GeV, is obtained for |q| = 2e particles, and the most stringent one, 1600 GeV, is for |q| = 6e particles.
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| 9. |
- Aad, G., et al.
(författare)
-
Search for pair-production of vector-like quarks in pp collision events at √s = 13 TeV with at least one leptonically decaying Z boson and a third-generation quark with the ATLAS detector
- 2023
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 843
-
Tidskriftsartikel (refereegranskat)abstract
- A search for the pair-production of vector-like quarks optimized for decays into a Z boson and a third-generation Standard Model quark is presented, using the full Run 2 dataset corresponding to 139 fb−1 of pp collisions at √s = 13 TeV, collected in 2015–2018 with the ATLAS detector at the Large Hadron Collider. The targeted final state is characterized by the presence of a Z boson with high transverse momentum, reconstructed from a pair of same-flavour leptons with opposite-sign charges, as well as by the presence of b-tagged jets and high-transverse-momentum large-radius jets reconstructed from calibrated smaller-radius jets. Events with exactly two or at least three leptons are used, which are further categorized by the presence of boosted W , Z, and Higgs bosons and top quarks. The categorization is performed using a neural-network-based boosted object tagger to enhance the sensitivity to signal relative to the background. No significant excess above the background expectation is observed and exclusion limits at 95% confidence level are set on the masses of the vector-like partners T and B of the top and bottom quarks, respectively. The limits depend on the branching ratio configurations and, in the case of 100% branching ratio for T → Zt and 100% branching ratio for B → Zb, this search sets the most stringent limits to date, allowing mT > 1.60 TeV and mB > 1.42 TeV, respectively.
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| 10. |
- Aad, G., et al.
(författare)
-
Search for pairs of muons with small displacements in pp collisions at √s=13 TeV with the ATLAS detector
- 2023
-
Ingår i: Physics Letters B. - : ELSEVIER. - 0370-2693 .- 1873-2445. ; 846
-
Tidskriftsartikel (refereegranskat)abstract
- A search for new phenomena giving rise to pairs of opposite electrically charged muons with impact parameters in the millimeter range is presented, using 139 fb−1 of √s=13 TeV pp collision data from the ATLAS detector at the LHC. The search targets the gap in coverage between existing searches targeting final states with leptons with large displacement and prompt leptons. No significant excess over the background expectation is observed and exclusion limits are set on the mass of long-lived scalar supersymmetric muon-partners (smuons) with much lower lifetimes than previously targeted by displaced muon searches. Smuon lifetimes down to 1 ps are excluded for a smuon mass of 100 GeV, and smuon masses up to 520 GeV are excluded for a proper lifetime of 10 ps, at 95% confidence level. Finally, model-independent limits are set on the contribution from new phenomena to the signal-region yields.
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| 11. |
- Aad, G., et al.
(författare)
-
Search for the Zγ decay mode of new high-mass resonances in pp collisions at √?=13 TeV with the ATLAS detector
- 2024
-
Ingår i: Physics Letters B. - 0370-2693 .- 1873-2445. ; 848
-
Tidskriftsartikel (refereegranskat)abstract
- This letter presents a search for narrow, high-mass resonances in the Zγ final state with the Z boson decaying into a pair of electrons or muons. The √?=13 TeV pp collision data were recorded by the ATLAS detector at the CERN Large Hadron Collider and have an integrated luminosity of 140 fb−1. The data are found to be in agreement with the Standard Model background expectation. Upper limits are set on the resonance production cross section times the decay branching ratio into Zγ. For spin-0 resonances produced via gluon–gluon fusion, the observed limits at 95% confidence level vary between 65.5 fb and 0.6 fb, while for spin-2 resonances produced via gluon–gluon fusion (or quark–antiquark initial states) limits vary between 77.4 (76.1) fb and 0.6 (0.5) fb, for the mass range from 220 GeV to 3400 GeV.
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| 12. |
- Andrean, Stefio Y., 1991-, et al.
(författare)
-
Comparison of inclusive and photon-tagged jet suppression in 5.02 TeV Pb+Pb collisions with ATLAS
- 2023
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 846
-
Tidskriftsartikel (refereegranskat)abstract
- Parton energy loss in the quark-gluon plasma (QGP) is studied with a measurement of photon-tagged jet production in 1.7 nb-1 of Pb+Pb data and 260 pb-1 of pp data, both at root sNN = 5.02 TeV, with the ATLAS detector. The process pp -> gamma +jet+X and its analogue in Pb+Pb collisions is measured in events containing an isolated photon with transverse momentum (pT) above 50 GeV and reported as a function of jet pT. This selection results in a sample of jets with a steeply falling pT distribution that are mostly initiated by the showering of quarks. The pp and Pb+Pb measurements are used to report the nuclear modification factor, RAA, and the fractional energy loss, Sloss, for photon-tagged jets. In addition, the results are compared with the analogous ones for inclusive jets, which have a significantly smaller quark-initiated fraction. The RAA and Sloss values are found to be significantly different between those for photon-tagged jets and inclusive jets, demonstrating that energy loss in the QGP is sensitive to the colour-charge of the initiating parton. The results are also compared with a variety of theoretical models of colour-charge-dependent energy loss. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons .org /licenses /by /4 .0/). Funded by SCOAP3.
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| 13. |
- Andrean, Stefio Y., 1991-, et al.
(författare)
-
Evidence of off-shell Higgs boson production from ZZ leptonic decay channels and constraints on its total width with the ATLAS detector
- 2023
-
Ingår i: Physics Letters B. - 0370-2693 .- 1873-2445. ; 846
-
Tidskriftsartikel (refereegranskat)abstract
- This Letter reports on a search for off-shell production of the Higgs boson using 139 fb−1fb−1 of pp collision data at √8 = 13 TeV collected by the ATLAS detector at the Large Hadron Collider. The signature is a pair of Z bosons, with contributions from both the production and subsequent decay of a virtual Higgs boson and the interference of that process with other processes. The two observable final states are ZZ→4ℓ and ZZ→2ℓ2ν with ℓ=e or μ. In the ZZ→4ℓ final state, a dense Neural Network is used to enhance analysis sensitivity with respect to matrix element-based discrimination. The background-only hypothesis is rejected with an observed (expected) significance of 3.3 (2.2) standard deviations, representing experimental evidence for off-shell Higgs boson production. Assuming that no new particles enter the production of the virtual Higgs boson, its total width can be deduced from the measurement of its off-shell production cross-section. The measured total width of the Higgs boson is 4.5+3.3−2.5 MeV, and the observed (expected) upper limit on the total width is found to be 10.5 (10.9) MeV at 95% confidence level.
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| 14. |
- Andrean, Stefio Y., 1991-, et al.
(författare)
-
Probing the CP nature of the top–Higgs Yukawa coupling in tt¯H??¯? and tH events with H→bb¯?→??¯ decays using the ATLAS detector at the LHC
- 2024
-
Ingår i: Physics Letters B. - : Elsevier B.V.. - 0370-2693 .- 1873-2445. ; 849
-
Tidskriftsartikel (refereegranskat)abstract
- The CP properties of the coupling between the Higgs boson and the top quark are investigated using 139 fb−1 of proton–proton collision data recorded by the ATLAS experiment at the LHC at a centre-of-mass energy of s√=13?=13 TeV. The CP structure of the top quark–Higgs boson Yukawa coupling is probed in events with a Higgs boson decaying into a pair of b-quarks and produced in association with either a pair of top quarks, tt¯H??¯?, or a single top quark, tH. Events containing one or two electrons or muons are used for the measurement. Multivariate techniques are used to select regions enriched in tt¯H??¯? and tH events, where dedicated CP-sensitive observables are exploited. In an extension of the Standard Model (SM) with a CP-odd admixture in the top–Higgs Yukawa coupling, the mixing angle between CP-even and CP-odd couplings is measured to be α=11∘+52∘−73∘?=11−73∘∘+52∘, compatible with the SM prediction corresponding to α=0?=0.
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| 15. |
- Mullier, G.A., et al.
(författare)
-
Observation of gauge boson joint-polarisation states in W± Z production from pp collisions at √s=13TeV with the ATLAS detector
- 2023
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 843
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of joint-polarisation states of W and Z gauge bosons in W±Z production are presented. The data set used corresponds to an integrated luminosity of 139 fb−1 of proton–proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. The W±Z candidate events are reconstructed using leptonic decay modes of the gauge bosons into electrons and muons. The simultaneous pair-production of longitudinally polarised vector bosons is measured for the first time with a significance of 7.1 standard deviations. The measured joint helicity fractions integrated over the fiducial region are f00=0.067±0.010, f0T=0.110±0.029, fT0=0.179±0.023 and fTT=0.644±0.032, in agreement with the next-to-leading-order Standard Model predictions. Individual helicity fractions of the W and Z bosons are also measured and found to be consistent with joint helicity fractions within the expected amounts of correlation. Both the joint and individual helicity fractions are also measured separately in W+Z and W−Z events. Inclusive and differential cross sections for several kinematic observables sensitive to polarisation are presented.
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| 16. |
- Mullier, Geoffrey A., et al.
(författare)
-
Observation of Wγγ triboson production in proton-proton collisions at √s=13 TeV with the ATLAS detector
- 2024
-
Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 848
-
Tidskriftsartikel (refereegranskat)abstract
- This letter reports the observation of ? (??)?? production in proton-proton collisions. This measurement uses the full Run 2 sample of events recorded at a center-of-mass energy of √s=13 TeV by the ATLAS detector at the LHC, corresponding to an integrated luminosity of 140 fb−1. Events with a leptonically-decaying W boson and at least two photons are considered. The background-only hypothesis is rejected with an observed and expected significance of 5.6 standard deviations. The inclusive fiducial production cross section of f ? (??)?? and ? (??)?? events is measured to be σfid= fb, in agreement with the Standard Model prediction.
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| 17. |
- Mullier, Geoffrey A., et al.
(författare)
-
Search for non-resonant production of semi-visible jets using Run 2 data in ATLAS
- 2024
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 848
-
Tidskriftsartikel (refereegranskat)abstract
- Semi-visible jets, with a significant contribution to the event's missing transverse momentum, can arise in strongly interacting dark sectors. This results in an event topology where one of the jets can be aligned with the direction of the missing transverse momentum. The first search for semi-visible jets produced via a t-channel mediator exchange is presented. The analysis uses proton-proton collisions with an integrated luminosity of 139 fb−1 and a centre-of-mass energy of 13 TeV, collected with the ATLAS detector during the Run 2 of the LHC. No excess over Standard Model predictions is observed. Assuming a coupling strength of unity between the mediator, a Standard Model quark and a dark quark, mediator masses up to 2.7 TeV are excluded at the 95% confidence level. Upper limits on the coupling strength are also derived.
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| 18. |
- Mullier, Geoffrey A., et al.
(författare)
-
Search for the decay of the Higgs boson to a Z boson and a light pseudoscalar particle decaying to two photons
- 2024
-
Ingår i: Physics Letters B. - : Elsevier B.V.. - 0370-2693 .- 1873-2445. ; 850
-
Tidskriftsartikel (refereegranskat)abstract
- A search for the decay of the Higgs boson to a Z boson and a light, pseudoscalar particle, a, decaying respectively to two leptons and to two photons is reported. The search uses the full LHC Run 2 proton–proton collision data at √?=13 TeV, corresponding to 139 fb−1 collected by the ATLAS detector. This is one of the first searches for this specific decay mode of the Higgs boson, and it probes unexplored parameter space in models with axion-like particles (ALPs) and extended scalar sectors. The mass of the a particle is assumed to be in the range 0.1–33 GeV. The data are analysed in two categories: a merged category where the photons from the a decay are reconstructed in the ATLAS calorimeter as a single cluster, and a resolved category in which two separate photons are detected. The main background processes are from Standard Model Z boson production in association with photons or jets. The data are in agreement with the background predictions, and upper limits on the branching ratio of the Higgs boson decay to Za times the branching ratio ?→?? are derived at the 95% confidence level and they range from 0.08% to 2% depending on the mass of the a particle. The results are also interpreted in the context of ALP models.
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| 19. |
- Petersson, Christoffer, 1979, et al.
(författare)
-
BARYONIC CORRECTIONS TO SUPERPOTENTIALS FROM PERTURBATION THEORY
- 2003
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 553:3-4, s. 332-336
-
Tidskriftsartikel (refereegranskat)abstract
- We study the corrections induced by a baryon vertex to the superpotential of SQCD with gauge group SU(N) and N quark flavors. We first compute the corrections order by order using a standard field theory technique and derive the corresponding glueball superpotential by "integrating in" the glueball field. The structure of the corrections matches with the expectations from the recently introduced perturbative techniques. We then compute the first non-trivial contribution using this new technique and find exact quantitative agreement. This involves cancellations between diagrams that go beyond the planar approximation.
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| 20. |
- Jones, R., et al.
(författare)
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Intrinsic defects and the D1 to D4 optical bands detected in plastically deformed Si
- 2000
-
Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 222:1, s. 133-140
-
Tidskriftsartikel (refereegranskat)abstract
- The properties of multi-vacancy and multi-interstitial defects that possess luminescent bands around 1 eV are reviewed. Prominent among these are the hexavacancy and tri- and tetra-self-interstitial defects. It is suggested that the formation of these defects on dislocation cores could lead to the D1 to D4 photoluminescent bands linked to dislocations in Si and SiGe.
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| 21. |
- Kordina, Olle, et al.
(författare)
-
Growth of SiC by "Hot-Wall" CVD and HTCVD
- 1997
-
Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 202:1, s. 321-334
-
Tidskriftsartikel (refereegranskat)abstract
- A reactor concept for the growth of high-quality epitaxial SiC films has been investigated. The reactor concept is based on a hot-wall type susceptor which, due to the unique design, is very power efficient. Four different susceptors are discussed in terms of quality and uniformity of the grown material. The films are grown using the silane–propane–hydrogen system on off-axis (0001) 6H- and 4H-SiC substrates. Layers with doping levels in the low 1014 cm—3 showing strong free exciton emission in the photoluminescence spectra may readily be grown reproducibly in this system. The quality of the grown layers is also confirmed by the room temperature minority carrier lifetimes in the microsecond range and the optically detected cyclotron resonance data which give mobilities in excess of 100000 cm2/Vs at 6 K. Finally, a brief description will be given of the HTCVD technique which shows promising results in terms of high quality material grown at high growth rates.
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| 22. |
- Monemar, Bo, 1942-, et al.
(författare)
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The 3.466 eV Bound Exciton in GaN
- 2001
-
Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 228:2, s. 489-492
-
Tidskriftsartikel (refereegranskat)abstract
- We discuss the available optical data for the 3.466 eV bound exciton in GaN, which has been a controversial issue in the recent literature. We conclude that the experimental results are only consistent with the identification as an exciton bound at a neutral acceptor with a spin-like bound hole. The chemical identity is still not clear.
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| 23. |
- Paskov, Plamen, 1959-, et al.
(författare)
-
Anisotropy of the in-plane strain in GaN grown on A-plane sapphire
- 2002
-
Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 234:3, s. 892-896
-
Tidskriftsartikel (refereegranskat)abstract
- A comparative study of GaN layer grown by hydride vapour phase epitaxy on A-plane sapphire before and after removal of the substrate is presented. A large anisotropy of the in-plane strain in the as-grown sample is revealed by X-ray diffraction measurements and polarized photoluminescence. The strain anisotropy is found to modify the selection rules for the transitions leading to a splitting of the optically active states of the A and B excitons. Almost complete strain relaxation and recovery of the optical isotropy in the (0001) plane is observed in the free-standing layer.
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| 24. |
- Paskov, Plamen, 1959-, et al.
(författare)
-
Internal structure of free excitons in GaN
- 2001
-
Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 228:2, s. 467-470
-
Tidskriftsartikel (refereegranskat)abstract
- Polarized photoluminescence is used to study the fine structure of free excitons in thick GaN layers grown on differently oriented sapphire substrates. The singlet-triplet splitting of the A exciton is measured and the exchange interaction constant in GaN is determined. For the samples grown on the a-plane sapphire, splitting of the A and B excitons induced by the uniaxial in-plane stress is also observed.
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| 25. |
- Paskov, Plamen, 1959-, et al.
(författare)
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Phonon-assisted photoluminescence in InGaN/GaN multiple quantum wells
- 2002
-
Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 234:3, s. 755-758
-
Tidskriftsartikel (refereegranskat)abstract
- The LO-phonon sidebands of the photoluminescence in InGaN/GaN multiple quantum wells has been investigated in the temperature range from 20 to 300 K. Analysing the intensity distribution among the phonon replicas, the strength of the exciton-phonon interaction has been estimated. The Huang-Rhys factor was found to be ÿ0.3, much larger than in GaN. The enhancement has been attributed to the exciton localization on a length scale smaller than the exciton Bohr radius and to the large internal electric field, which increases the spatial separation of the electron and hole charge densities along the growth axis.
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