Experimental study of the correlation length of critical-current fluctuations in the presence of surface disorder: Probing vortex long-range interactions

We report on critical currents and voltage noise measurements in Niobium strips in the superconducting state, in the presence of a bulk vortex lattice ($B < B_{C2}$) and in the surface superconducting state ($B_{c2}< B < B_{C3}$). For homogeneous surfaces, the correlation length of the current fluctuations can be associated with the electromagnetic skin depth of vortex superficial instabilities. The modification of the surface state by means of low energy irradiation induces a strong modification of the critical current and of the noise. The appearance of a corner frequency in the spectral domain can be linked with the low wave-vectors of the artificial corrugation. Since this latter occurs only for $B < B_{C2}$, we propose that the long-range interactions allow the correlation length to extend up to values imposed by the surface topography.Comment: accepted for publication in PR

Correlation between Ferromagnetic Layer Easy Axis and the Tilt Angle of Self Assembled Chiral Molecules

The spin-spin interactions between chiral molecules and ferromagnetic metals were found to be strongly affected by the chiral induced spin selectivity effect. Previous works unraveled two complementary phenomena: magnetization reorientation of ferromagnetic thin film upon adsorption of chiral molecules and different interaction rate of opposite enantiomers with a magnetic substrate. These phenomena were all observed when the easy axis of the ferromagnet was out of plane. In this work, the effects of the ferromagnetic easy axis direction, on both the chiral molecular monolayer tilt angle and the magnetization reorientation of the magnetic substrate, are studied using magnetic force microscopy. We have also studied the effect of an applied external magnetic field during the adsorption process. Our results show a clear correlation between the ferromagnetic layer easy axis direction and the tilt angle of the bonded molecules. This tilt angle was found to be larger for an in plane easy axis as compared to an out of plane easy axis. Adsorption under external magnetic field shows that magnetization reorientation occurs also after the adsorption event. These findings show that the interaction between chiral molecules and ferromagnetic layers stabilizes the magnetic reorientation, even after the adsorption, and strongly depends on the anisotropy of the magnetic substrate. This unique behavior is important for developing enantiomer separation techniques using magnetic substrates

Vortex avalanches and self organized criticality in superconducting niobium

In 1993 Tang proposed [1] that vortex avalanches should produce a self organized critical state in superconductors, but conclusive evidence for this has heretofore been lacking. In the present paper, we report extensive micro-Hall probe data from the vortex dynamics in superconducting niobium, where a broad distribution of avalanche sizes scaling as a power-law for more than two decades is found. The measurements are combined with magneto-optical imaging, and show that over a widely varying magnetic landscape the scaling behaviour does not change, hence establishing that the dynamics of superconducting vortices is a SOC phenomenon.Comment: 3 pages + 4 figures, a reference added, citation typos fixe

Gestational diabetes as a risk factor for pancreatic cancer: a prospective cohort study

<p>Abstract</p> <p>Background</p> <p>Diabetes is known to be associated with cancer of the pancreas, though there is some debate as to whether it is a cause or a consequence of the disease. We investigated the incidence of pancreatic cancer in a cohort of 37926 Israeli women followed for 28–40 years for whom information on diabetes had been collected at the time they gave birth, in 1964–1976, in Jerusalem. There were 54 cases of pancreatic cancer ascertained from the Israel Cancer Registry during follow-up.</p> <p>Methods</p> <p>We used Cox proportional hazards models to adjust for age at baseline and explore effects of other risk factors, including ethnic groups, preeclampsia, birth order and birth weight of offspring.</p> <p>Results</p> <p>We observed no cases of pancreatic cancer in the women with insulin dependent diabetes; however, there were five cases in the women with gestational diabetes. The interval between the record of diabetes in pregnancy and the diagnosis of pancreatic cancer ranged from 14–35 years. Women with a history of gestational diabetes showed a relative risk of pancreatic cancer of 7.1 (95% confidence interval, 2.8–18.0).</p> <p>Conclusion</p> <p>We conclude that gestational diabetes is strongly related to the risk of cancer of the pancreas in women in this population, and that gestational diabetes can precede cancer diagnosis by many years.</p

Equilibration and Dynamic Phase Transitions of a Driven Vortex Lattice

We report on the observation of two types of current driven transitions in metastable vortex lattices. The metastable states, which are missed in usual slow transport measurements, are detected with a fast transport technique in the vortex lattice of undoped 2H-NbSe$_2$. The transitions are seen by following the evolution of these states when driven by a current. At low currents we observe an equilibration transition from a metastable to a stable state, followed by a dynamic crystallization transition at high currents.Comment: 5 pages, 4 figure

Magnetization switching in ferromagnets by adsorbed chiral molecules without current or external magnetic field

Ferromagnets are commonly magnetized by either external magnetic fields or spin polarized currents. The manipulation of magnetization by spin-current occurs through the spin-transfer-torque effect, which is applied, for example, in modern magnetoresistive random access memory. However, the current density required for the spin-transfer torque is of the order of 1 × 106 A·cm−2, or about 1 × 1025 electrons s−1 cm−2. This relatively high current density significantly affects the devices’ structure and performance. Here we demonstrate magnetization switching of ferromagnetic thin layers that is induced solely by adsorption of chiral molecules. In this case, about 1013 electrons per cm2 are sufficient to induce magnetization reversal. The direction of the magnetization depends on the handedness of the adsorbed chiral molecules. Local magnetization switching is achieved by adsorbing a chiral self-assembled molecular monolayer on a gold-coated ferromagnetic layer with perpendicular magnetic anisotropy. These results present a simple low-power magnetization mechanism when operating at ambient conditions

Weiss Oscillations in Surface Acoustic Wave Propagation

The interaction of a surface acoustic wave (SAW) with a a two-dimensional electron gas in a periodic electric potential and a classical magnetic field is considered. We calculate the attenuation of the SAW and its velocity change and show that these quantities exhibit Weiss oscillations.Comment: 4 pages REVTEX, 2 figures included as eps file

Separation of enantiomers by their enantiospecific interaction with achiral magnetic substrates

It is commonly assumed that recognition and discrimination of chirality, both in nature and in artificial systems, depend solely on spatial effects. However, recent studies have suggested that charge redistribution in chiral molecules manifests an enantiospecific preference in electron spin orientation. We therefore reasoned that the induced spin polarization may affect enantiorecognition through exchange interactions. Here we show experimentally that the interaction of chiral molecules with a perpendicularly magnetized substrate is enantiospecific. Thus, one enantiomer adsorbs preferentially when the magnetic dipole is pointing up, whereas the other adsorbs faster for the opposite alignment of the magnetization. The interaction is not controlled by the magnetic field per se, but rather by the electron spin orientations, and opens prospects for a distinct approach to enantiomeric separations

History effects and pinning regimes in solid vortex matter

We propose a phenomenological model that accounts for the history effects observed in ac susceptibility measurements in YBa2Cu3O7 single crystals [Phys. Rev. Lett. 84, 4200 (2000) and Phys. Rev. Lett. 86, 504 (2001)]. Central to the model is the assumption that the penetrating ac magnetic field modifies the vortex lattice mobility, trapping different robust dynamical states in different regions of the sample. We discuss in detail on the response of the superconductor to an ac magnetic field when the vortex lattice mobility is not uniform inside the sample. We begin with an analytical description for a simple geometry (slab) and then we perform numerical calculations for a strip in a transverse magnetic field which include relaxation effects. In calculations, the vortex system is assumed to coexist in different pinning regimes. The vortex behavior in the regions where the induced current density j has been always below a given threshold (j_c^>) is described by an elastic Campbell-like regime (or a critical state regime with local high critical current density, j_c^>). When the VS is shaken by symmetrical (e.g. sinusoidal) ac fields, the critical current density is modified to j_c^) at regions where vortices have been forced to oscillate by a current density larger than j_c^>. Experimentally, an initial state with high critical current density (j_c^>) can be obtained by zero field cooling, field cooling (with no applied ac field) or by shaking the vortex lattice with an asymmetrical (e.g. sawtooth) field. We compare our calculations with experimental ac susceptibility results in YBa2Cu3O7 single crystals.Comment: 11 pages, 7 figures. To be published in PR