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- Bray, C., et al.
(författare)
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Temperature-dependent zero-field splittings in graphene
- 2022
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 106:24
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Tidskriftsartikel (refereegranskat)abstract
- Graphene is a quantum spin Hall insulator with a 45μeV-wide nontrivial topological gap induced by the intrinsic spin-orbit coupling. Even though this zero-field spin splitting is weak, it makes graphene an attractive candidate for applications in quantum technologies, given the resulting long spin-relaxation time. On the other side, the staggered sublattice potential, resulting from the coupling of graphene with its boron nitride substrate, compensates intrinsic spin-orbit coupling and decreases the nontrivial topological gap, which may lead to the phase transition into trivial band insulator state. In this work, we present extensive experimental studies of the zero-field splittings in monolayer and bilayer graphene in a temperature range 2-12 K by means of subterahertz photoconductivity-based electron spin-resonance technique. Surprisingly, we observe a decrease of the spin splittings with increasing temperature. We discuss the origin of this phenomenon by considering possible physical mechanisms likely to induce a temperature dependence of the spin-orbit coupling. These include the difference in the expansion coefficients between the graphene and the boron nitride substrate or the metal contacts, the electron-phonon interactions, and the presence of a magnetic order at low temperature. Our experimental observation expands knowledge about the nontrivial topological gap in graphene.
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- Maussang, K., et al.
(författare)
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Temperature dependance of Intrinsic Spin Orbit Coupling Gap in Graphene probed by Terahertz photoconductivity
- 2023
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Ingår i: International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz. - 2162-2027 .- 2162-2035.
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Konferensbidrag (refereegranskat)abstract
- Graphene is a quantum spin Hall insulator, with a nontrivial topological gap induced by the spin-orbit coupling. Such splitting is weak (∼ 45 μ eV) in the absence of external magnetic field. However, due to rather long spin-relaxation time, graphene is an attractive candidate for applications in quantum technologies. When it is encapsulated in hexagonal boron nitride, the coupling between graphene and the substrate compensates intrinsic spin-orbit coupling and decreases the nontrivial topological gap, which may lead to phase transition into a trivial band insulator state. In this work, we have measured experimentally the zero-field splittings in monolayer and bilayer graphene by the means of subterahertz photoconductivity-based electron spin resonance technique. The dependance in temperature of such splittings have been also studied in the 2-12K range. We observed a decrease of the spin splittings with increasing temperature. Such behavior might be understood from several physical mechanisms that could induce a temperature dependence of the spin-orbit coupling. These includes the difference in the expansion coefficients between the graphene and the boron nitride substrate or the metal contacts, the electronphonon interactions, and the presence of a magnetic order at low temperature.
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- Pirkis, Jane, et al.
(författare)
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Suicide numbers during the first 9-15 months of the COVID-19 pandemic compared with pre-existing trends : An interrupted time series analysis in 33 countries
- 2022
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Ingår i: eClinicalMedicine. - : Elsevier. - 2589-5370. ; 51
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Tidskriftsartikel (refereegranskat)abstract
- Background Predicted increases in suicide were not generally observed in the early months of the COVID-19 pandemic. However, the picture may be changing and patterns might vary across demographic groups. We aimed to provide a timely, granular picture of the pandemic's impact on suicides globally. Methods We identified suicide data from official public-sector sources for countries/areas-within-countries, searching websites and academic literature and contacting data custodians and authors as necessary. We sent our first data request on 22nd June 2021 and stopped collecting data on 31st October 2021. We used interrupted time series (ITS) analyses to model the association between the pandemic's emergence and total suicides and suicides by sex-, age-and sex-by-age in each country/area-within-country. We compared the observed and expected numbers of suicides in the pandemic's first nine and first 10-15 months and used meta-regression to explore sources of variation. Findings We sourced data from 33 countries (24 high-income, six upper-middle-income, three lower-middle-income; 25 with whole-country data, 12 with data for area(s)-within-the-country, four with both). There was no evidence of greater-than-expected numbers of suicides in the majority of countries/areas-within-countries in any analysis; more commonly, there was evidence of lower-than-expected numbers. Certain sex, age and sex-by-age groups stood out as potentially concerning, but these were not consistent across countries/areas-within-countries. In the meta-regression, different patterns were not explained by countries' COVID-19 mortality rate, stringency of public health response, economic support level, or presence of a national suicide prevention strategy. Nor were they explained by countries' income level, although the meta-regression only included data from high-income and upper-middle-income countries, and there were suggestions from the ITS analyses that lower-middle-income countries fared less well. Interpretation Although there are some countries/areas-within-countries where overall suicide numbers and numbers for certain sex- and age-based groups are greater-than-expected, these countries/areas-within-countries are in the minority. Any upward movement in suicide numbers in any place or group is concerning, and we need to remain alert to and respond to changes as the pandemic and its mental health and economic consequences continue. Copyright (C) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
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- Ray, K. K., et al.
(författare)
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EU-Wide Cross-Sectional Observational Study of Lipid-Modifying Therapy Use in Secondary and Primary Care: the DA VINCI study
- 2021
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Ingår i: European Journal of Preventive Cardiology. - : Oxford University Press (OUP). - 2047-4873 .- 2047-4881. ; 28:11, s. 1279-1289
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Tidskriftsartikel (refereegranskat)abstract
- Aims To provide contemporary data on the implementation of European guideline recommendations for lipid-lowering therapies (LLTs) across different settings and populations and how this impacts low-density lipoprotein cholesterol (LDL-C) goal achievement. Methods and results An 18 country, cross-sectional, observational study of patients prescribed LLT for primary or secondary prevention in primary or secondary care across Europe. Between June 2017 and November 2018, data were collected at a single visit, including LLT in the preceding 12 months and most recent LDL-C. Primary outcome was the achievement of risk-based 2016 European Society of Cardiology (ESC)/European Atherosclerosis Society (EAS) LDL-C goal while receiving stabilized LLT; 2019 goal achievement was also assessed. Overall, 5888 patients (3000 primary and 2888 secondary prevention patients) were enrolled; 54% [95% confidence interval (CI) 52-56] achieved their risk-based 2016 goal and 33% (95% CI 32-35) achieved their risk-based 2019 goal. High-intensity statin monotherapy was used in 20% and 38% of very high-risk primary and secondary prevention patients, respectively. Corresponding 2016 goal attainment was 22% and 45% (17% and 22% for 2019 goals) for very high-risk primary and secondary prevention patients, respectively. Use of moderate-high-intensity statins in combination with ezetimibe (9%), or any LLT with PCSK9 inhibitors (1%), was low; corresponding 2016 and 2019 goal attainment was 53% and 20% (ezetimibe combination), and 67% and 58% (PCSK9i combination). Conclusion Gaps between clinical guidelines and clinical practice for lipid management across Europe persist, which will be exacerbated by the 2019 guidelines. Even with optimized statins, greater utilization of non-statin LLT is likely needed to reduce these gaps for patients at highest risk.
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