Biomedical subjects

D Mailly

Publications and source records attributed to D Mailly.

17 recordsLinked to original sources

PubMed2002

Diamagnetic orbital response of mesoscopic silver rings.

We report measurements of the flux-dependent orbital magnetic susceptibility of an ensemble of 10(5) disconnected silver rings at 217 MHz. Because of the strong spin-orbit scattering rate in silver this experiment is a test of existing theories on ensemble averaged persistent currents. Below 100 mK the rings exhibit a magnetic signal with a flux periodicity of h/2e consistent with averaged persistent currents, whose amplitude is of the order of 0.3 nA. The sign of the oscillations indicates unambiguously diamagnetism in the vicinity of zero magnetic field. This sign is a priori not consistent with theoretical predictions for average persistent currents. We discuss several possible explanations of this result.

Journal Article↗

PubMed2001

Nuclear spin driven quantum relaxation in LiY0.998Ho0.002F4.

Staircaselike hysteresis loops of the magnetization of a LiY0.998Ho0.002F4 single crystal are observed at subkelvin temperatures and low field sweep rates. This behavior results from quantum dynamics at avoided level crossings of the energy spectrum of single Ho3+ ions in the presence of hyperfine interactions. Enhanced quantum relaxation in constant transverse fields allows the study of the relative magnitude of tunnel splittings. At faster sweep rates, nonequilibrated spin-phonon and spin-spin transitions, mediated by weak dipolar interactions, lead to magnetization oscillations and additional steps.

Journal Article↗

PubMed2001

Aharonov-Bohm cages in 2D normal metal networks.

We report on magnetoresistance transport measurements performed on a bipartite tiling of rhombus in the GaAs/GaAlAs system. We observe for the first time large amplitude h/e oscillations in this network as compared to the one measured in square lattices of similar size. These oscillations are the signature of a recently predicted localization phenomenon induced by Aharonov-Bohm interferences in this peculiar network.

Journal Article↗

PubMed2001

Magnetic anisotropy of a single cobalt nanocluster.

Using a new micro-SQUID setup, we investigate magnetic anisotropy in a single 1000-atom cobalt cluster. This system opens new fields in the characterization and understanding of the origin of magnetic anisotropy in such nanoparticles. For this purpose, we report three-dimensional switching field measurements performed on a 3 nm cobalt cluster embedded in a niobium matrix. We are able to separate the different magnetic anisotropy contributions and evidence the dominating role of the cluster surface.

Journal Article↗

PubMed2001

Persistent currents in mesoscopic connected rings.

We report measurements of the low temperature magnetic response of a line of 16 GaAs/GaAlAs connected mesoscopic rings whose total length is much larger than l(straight phi). Using an on-chip micro-SQUID technology, we have measured a periodic response, with period h/e, corresponding to persistent currents in the rings of a typical amplitude of 0.40+/-0.08 nA per ring. Direct comparison with measurements on the same rings but isolated is presented.

Journal Article↗

PubMed2000

Measurements of flux-dependent screening in aharonov-bohm rings

In order to investigate the effect of electronic phase coherence on screening we have measured the flux-dependent polarizability of isolated mesoscopic rings at 350 MHz. At low temperatures (below 100 mK) both the nondissipative and the dissipative parts of the polarizability exhibit flux oscillations with a period of one-half a flux quantum in a ring. The sign and amplitude of the effect are in good agreement with recent theoretical predictions. The observed positive magnetopolarizability corresponds to an enhancement of screening when time reversal symmetry is broken. The effect of electronic density and temperature are also measured.

Journal Article↗

PubMed2000

Detection of doubled shot noise in short normal-metal/superconductor junctions

Shot noise refers to the fluctuations in electrical current through a device arising from the discrete nature of the charge-carrying particles. Recent experiments have exploited the fact that the shot noise is proportional to the charge of the carriers to establish fractional quantization of quasiparticles in the fractional quantum Hall effect. By a similar argument, it is expected that when a superconducting reservoir emits Cooper pairs, (which have a charge twice that of an electron) into a short normal-metal wire, the shot noise should be double that obtained for a normal-metal reservoir. Although the charge of Cooper pairs has been well established by flux quantization and tunnel experiments, doubling of their shot noise has not yet been observed. Here we report a shot-noise experiment using a short diffusive normal-metal superconductor contact, in which we confirm the predicted noise behaviour for double charges. The measurements, taken over a large range of bias current, establish that phase coherence is not required to observe the effect.

Journal Article↗

PubMed1996