No abstract

No abstract

-(BETS) 2 FeCl 4 undergoes transitions from an antiferromagnetic insulator to a metal and then to a superconductor as a magnetic field is increased. We use a Hubbard-Kondo model to clarify the role of the Fe 3ϩ magnetic ions in these phase transitions. In the high-field regime, the magnetic field acting on the electron spins is compensated by the exchange field H e due to the magnetic ions. We show how H e can be extracted from the observed splitting of the Shubnikov-de Haas frequencies. We predict the field range for field-induced superconductivity in other materials. DOI: 10.1103/PhysRevB.65.100502 PACS number͑s͒: 74.70.Kn, 75.30.Kz The discovery of magnetic-field-induced superconductivity 1 in the two-dimensional compound -(BETS) 2 FeCl 4 ͓where BETS is bis͑ethylenedithio͒-tetraselenafulvalene͔ is an example of the rich phase diagrams of organic molecular crystals.2 Whereas, previously, pressure or chemical substitution has been used to change the electronic properties of these organic materials, it is remarkable that this compound undergoes successive electronic phase transitions as the magnetic field is increased. Below a temperature of 8 K, -(BETS) 2 FeCl 4 is an antiferromagnetic ͑AF͒ insulator.3 As a magnetic field is applied, it undergoes a first-order transition to a metal at 11 T. Close to this field, the magnetic moments associated with the spin 5/2 of the Fe 3ϩ ions undergo a transition to a polarized paramagnet. If the magnetic field is parallel to the layers, there is a transition to a superconductor at 20 T, 1 which is then destroyed above 42 T. 4 The magnetic ions are essential to this behavior, since the compound with nonmagnetic ions, -(BETS) 2 GaCl 4 , is, in contrast, a superconductor at zero field, 5 despite very similar crystal structures. 6 In this Communication we focus on three questions: ͑i͒ Why does the inclusion of magnetic ions change the ground state from a superconductor to an insulator? ͑ii͒ Is the magnetic-field-induced superconductivity due to the the Jaccarino-Peter effect, 4,7 where the external field is compensated by an internal exchange field due to the magnetic ions? and ͑iii͒ Does the Jaccarino-Peter picture survive if one takes into account the spin fluctuations associated with the magnetic ions?Recently, Ziman introduced a two-dimensional HubbardKondo model in order to understand question ͑i͒.3 The model takes into account the four conduction bands associated with layers of BETS molecules ͓four highest occupied molecular orbitals ͑HOMO͒ per unit cell͔, a Kondo coupling between the localized Sϭ5/2 spins and the conduction electrons, and the Coulomb repulsion between two electrons on the same BETS molecule. Ziman found that for small electronelectron repulsion the periodic potential due to the magnetic ordering ͑found self-consistently͒ at low temperature opens energy gaps on the Fermi surface.3 A magnetic field, by aligning the moments, destroys the periodic potential, restoring the Fermi surface. However, to suppress the entire Fermi surface, this needs a Kondo cou...

Context: Representativeness of 'standard' antihypertensive drug trials is uncertain, with limited recruitment of older people. Some trials specifically recruit older participants to address this. Trials are obliged to report hospitalizations and deaths, regardless of cause, as Serious Adverse Events (SAEs). If older-people's trials are representative, we would expect rates of SAEs in trials to be similar to the rate of hospitalisation and death in the community, and higher than standard trials. Objective: To compare the rate of SAEs in hypertension trials to rates of hospitalisation and death among people taking similar treatments in the community. Study Design: Observational study comparing trial populations to a community cohort. Dataset: We identified trials of Renin-Angiotensin-Aldosterone system (RAAS) drugs for hypertension from clinicatrials.gov. We identified a community comparison population of people with hypertension starting RAAS drugs using primary care data from the Wales, UK (SAIL databank). Population studied: Trial participants from 110 RAAS hypertension trials (11 older-people's trials, mean age 73, and 99 standard trials, mean age 56). Community cohort of people with hypertension (n=56,036, mean age 60) starting RAAS drugs. Outcomes: SAEs in trials (mostly accounted for by hospitalizations or deaths) and all-cause hospitalizations/deaths in the community comparison. SAE rates in older-people and standard trials were compared, adjusting for trial characteristics. The community rate was used to calculate the expected rate of hospitalizations/deaths given the age/sex distribution of each trial. We then compared the expected rate with the observed rate of SAEs in each trial. Results: Older-people's trials had higher SAEs rate than standard trials (0.18 versus 0.11 events/person/year, adjusted IRR 1.74, 95% CI 1.03-2.92). The hospitalisation and death rate in the community for those taking RAAS antihypertensives was much greater than the rate of SAEs reported in standard (ratio 3.70 (3.12-4.55)) and older-people's trials (4. 35 (2.56-7.69)), adjusting for age and sex. Conclusion: Trials report substantially fewer SAEs than expected from rates of hospitalisations and deaths among similar-aged people receiving equivalent treatments in the community. SAE rates may be a useful metric to assess trial representativeness. Clinicians should be cautious when applying trial recommendations to older people, even when trials focus on older people.