Magnetic properties of HO2 thin films

We report on the magnetic and transport studies of hafnium oxide thin films grown by pulsed-laser deposition on sapphire substrates under different oxygen pressures, ranging from 10-7 to 10-1 mbar. Some physical properties of these thin films appear to depend on the oxygen pressure during growth: the film grown at low oxygen pressure (P ~= 10-7 mbar) has a metallic aspect and is conducting, with a positive Hall signal, while those grown under higher oxygen pressures (7 x 10-5 <= P <= 0.4 mbar) are insulating. However, no intrinsic ferromagnetic signal could be attributed to the HfO2 films, irrespective of the oxygen pressure during the deposition.Comment: 1

Non-monotonic field-dependence of the ZFC magnetization peak in some systems of magnetic nanoparticles

We have performed magnetic measurements on a diluted system of gamma-Fe2O3 nanoparticles (~7nm), and on a ferritin sample. In both cases, the ZFC-peak presents a non-monotonic field dependence, as has already been reported in some experiments,and discussed as a possible evidence of resonant tunneling. Within simple assumptions, we derive expressions for the magnetization obtained in the usual ZFC, FC, TRM procedures. We point out that the ZFC-peak position is extremely sensitive to the width of the particle size distribution, and give some numerical estimates of this effect. We propose to combine the FC magnetization with a modified TRM measurement, a procedure which allows a more direct access to the barrier distribution in a field. The typical barrier values which are obtained with this method show a monotonic decrease for increasing fields, as expected from the simple effect of anisotropy barrier lowering, in contrast with the ZFC results. From our measurements on gamma-Fe2O3 particles, we show that the width of the effective barrier distribution is slightly increasing with the field, an effect which is sufficient for causing the observed initial increase of the ZFC-peak temperatures.Comment: LaTeX file 19 pages, 9 postscript figures. To appear in Phys. Rev. B (tentative schedule: Dec.97

Granularity-induced gapless superconductivity in NbN films: evidence of thermal phase fluctuations

Using a single coil mutual inductance technique, we measure the low temperature dependence of the magnetic penetration depth in superconducting NbN films prepared with similar critical temperatures around 16 K but with different microstructures. Only (100) epitaxial and weakly granular (100) textured films display the characteristic exponential dependence of conventional BCS s-wave superconductors. More granular (111) textured films exhibit a linear dependence, indicating a gapless state in spite of the s-wave gap. This result is quantitatively explained by a model of thermal phase fluctuations favored by the granular structure.Comment: 10 pages, 4 figures, to appear in Phys. Rev.

Pseudogap in a thin film of a conventional superconductor

A superconducting state is characterized by the gap in the electronic density of states which vanishes at the superconducting transition temperature Tc. It was discovered that in high temperature superconductors a noticeable depression in the density of states still remains even at temperatures above Tc; this feature being called pseudogap. Here we show that a pseudogap exists in a conventional superconductor: ultrathin titanium nitride films over a wide range of temperatures above Tc. Our study reveals that this pseudogap state is induced by superconducting fluctuations and favored by two-dimensionality and by the proximity to the transition to the insulating state. A general character of the observed phenomenon provides a powerful tool to discriminate between fluctuations as the origin of the pseudogap state, and other contributions in the layered high temperature superconductor compounds.Comment: 26 pages, 4 figure

Localization of preformed Cooper pairs in disordered superconductors

International audienceThe most profound effect of disorder on electronic systems is the localization of the electrons transforming an otherwise metallic system into an insulator. If the metal is also a superconductor then, at low temperatures, disorder can induce a pronounced transition from a superconducting into an insulating state. An outstanding question is whether the route to insulating behaviour proceeds through the direct localization of Cooper pairs or, alternatively, by a two-step process in which the Cooper pairing is first destroyed followed by the standard localization of single electrons. Here we address this question by studying the local superconducting gap of a highly disordered amorphous superconductor by means of scanning tunnelling spectroscopy. Our measurements reveal that, in the vicinity of the superconductor-insulator transition, the coherence peaks in the one-particle density of states disappear whereas the superconducting gap remains intact, indicating the presence of localized Cooper pairs. Our results provide the first direct evidence that the superconductor-insulator transition in some homogeneously disordered materials is driven by Cooper-pair localization

Behavioural evidence for self-medication in bumblebees?

The presence of antimicrobial secondary metabolites in nectar suggests that pollinators, which are threatened globally by emergent disease, may benefit from the consumption of nectars rich in these metabolites. We tested whether nicotine, a nectar secondary metabolite common in Solanaceae and Tilia species, is used by parasitized bumblebees as a source of self-medication , using a series of toxicological, microbiological and behavioural experiments. Caged bees infected with Crithidia bombi had a slight preference for sucrose solution laced with the alkaloid and behavioural tests showed that the parasite infection induced an increased consumption of nicotine during foraging activity, though nicotine had an appetite-reducing effect overall. When ingested, nicotine delayed the progression of a gut infection in bumblebees by a few days, but dietary nicotine did not clear the infection, and after 10 days the parasite load approached that of control bees. Moreover, when pathogens were exposed to the alkaloid prior to host ingestion, the protozoan's viability was not directly affected, suggesting that anti-parasite effects were relatively weak. Nicotine consumption in a single dose did not impose any cost even in starved bees but the alkaloid had detrimental effects on healthy bees if consistently consumed for weeks. These toxic effects disappeared in infected bees, suggesting that detoxification costs might have been counterbalanced by the advantages in slowing the progression of the infection. Nicotine consumption did not affect bee lifespan but the reduction in the parasite load may have other likely unexplored subtle benefits both for individual bees and their colony.  Potential evidence for self-medication is discussed. The contention that secondary metabolites in nectar may be under selection from pollinators, or used by plants to enhance their own reproductive success, remains to be confirmed.D.B. was supported by a Marie Curie Intra European Fellowship within the 7th European Community Framework Programm

Telaprevir-based therapy for treatment of HIV-1 and hepatitis C virus co-infected patients : An early access programme

Objectives: HPC3005 is a multicentre, open-label, telaprevir trial in HCV/HIV coinfected patients with severe fibrosis or compensated cirrhosis. Methods: Patients were treated with telaprevir 750 mg every 8 h (1125 mg if on efavirenz) plus pegylated interferon-alpha (PEG-IFN, 180 \u3bcg once-weekly) and ribavirin (RBV, 800 mg/day) for 12 weeks, followed by 36 weeks of PEG-IFN/RBV. Results: Mean age was 44 years, 97/118 patients were male and all were Caucasian, 68 had severe fibrosis and 50 had cirrhosis. Seventy-eight had HCV RNA levels 65800 000 IU/mL, 72 had HCV genotype 1a, baseline HIV RNA was <50 copies/mL in 112 patients. Overall, 114/118 patients continued antiretroviral treatment, 4 were untreated. Seventy-five patients received tenofovir and 74 emtricitabine; in addition 53 received atazanavir/ritonavir, 43 raltegravir, and 24 efavirenz. By intention-to-treat, 78 (66%) patients achieved SVR24. Nineteen discontinued telaprevir, 8 for virological endpoint, 5 for adverse events (2 anaemia, 2 rash, 1 asthenia), 5 for non-compliance and 1 withdrew consent. The most common adverse events were anaemia (36 patients), thrombocytopaenia (33), rash (26), bilirubin increase (17), and neutropenia (16). Conclusions: In this early access programme in coinfected patients with severe fibrosis or cirrhosis, 66% of patients achieved SVR. The most common adverse events were haematological. Clinical Trial Number: NCT01500616