Observation of superspin glass state in magnetically textured ferrofluid (gamma-Fe2O3)

Magnetic properties in a magnetically textured ferrofluid made out of interacting maghemite (gamma-Fe2O3) nanoparticles suspended in glycerin have been investigated. Despite the loss of uniform distribution of anisotropy axes, a superspin glass state exists at low temperature in a concentrated, textured ferrofluid as in the case of its non-textured counterpart. The onset of superspin glass state was verified from the sample's AC susceptibility. The influence of the anisotropy axis orientation on the aging behavior in the glassy states is also discussed

Real time decoherence of Landau and Levitov quasi-particles in quantum Hall edge channels

Quantum Hall edge channels at integer filling factor provide a unique test-bench to understand decoherence and relaxation of single electronic excitations in a ballistic quantum conductor. In this Letter, we obtain a full visualization of the decoherence scenario of energy (Landau) and time (Levitov) resolved single electron excitations at filling factor $\nu=2$. We show that the Landau excitation exhibits a fast relaxation followed by spin-charge separation whereas the Levitov excitation only experiences spin-charge separation. We finally suggest to use Hong-Ou-Mandel type experiments to probe specific signatures of these different scenarios.Comment: 14 pages, 8 figure

Simultaneous and accurate measurement of the dielectric constant at many frequencies spanning a wide range

We present an innovative technique which allows the simultaneous measurement of the dielectric constant of a material at many frequencies, spanning a four orders of magnitude range chosen between 10 --2 Hz and 10 4 Hz. The sensitivity and accuracy are comparable to those obtained using standard single frequency techniques. The technique is based on three new and simple features: a) the precise real time correction of the amplication of a current amplier; b) the specic shape of the excitation signal and its frequency spectrum; and c) the precise synchronization between the generation of the excitation signal and the acquisition of the dielectric response signal. This technique is useful in the case of relatively fast dynamical measurements when the knowledge of the time evolution of the dielectric constant is needed

Experimental search for dynamic heterogeneities in molecular glass formers

We have measured the linear dielectric susceptibility of two molecular glass formers close to Tg in order to estimate the size of the dynamically correlated clusters of molecules which are expected to govern the physics of glass formation. This size has been shown to be related to the dynamic dielectric susceptibility dEps(w)/dT (Eps : dielectric susceptibility, T : temperature, w&#61472;: frequency). To allow for an accurate determination of the T derivative, we scanned the interval 192 < T < 232 K every 1 K for glycerol and 159 < T < 179 K every 0.5 K for propylene carbonate. The resolution on T variations was about 1 mK. The result for glycerol is that the number of correlated molecules increases by a factor 3 when T goes from 226 to 195 K. It has been shown that the non-linear susceptibility provides a direct measurement of dynamic correlations. To measure it, we used a standard Lockin technique yielding the third harmonic of the current flowing out of a capacitor. We obtained only an upper limit on the ratio of the third to the first harmonic, due to the non-linear response of standard electronics.Comment: 7 page

Superspin glass aging behavior in textured and nontextured frozen ferrofluid

The effect of magnetic anisotropy-axis alignment of individual nanoparticles on the collective aging behavior in the superspin glass state of a frozen ferrofluid has been investigated. The ferrofluid studied here consists of maghemite nanoparticles (\gamma-Fe2O3, mean diameter = 8.6 nm) dispersed in glycerin at a volume fraction of ~15%. The low temperature aging behavior has been explored through 'zero-field cooled magnetization' (ZFCM) relaxation measurements using SQUID magnetometry. The ZFCM response functions were found to scale with effective age of the system in both textured and non-textured superspin glass states, but with markedly different scaling exponents, \mu. The value of {\mu} was found to shift from ~0.9 in non-textured case to ~ 0.6 in the textured case, despite the identical cooling protocol used in both experiments

Anisotropy-axis orientation effect on the magnetization of {\gamma}-Fe2O3 frozen ferrofluid

The effect of magnetic anisotropy-axis alignment on the superparamagnetic (SPM) and superspin glass (SSG) states in a frozen ferrofluid has been investigated. The ferrofluid studied here consists of maghemite nanoparticles (\gamma-Fe2O3, mean diameter = 8.6 nm) dispersed in glycerine at a volume fraction of ~15%. In the high temperature SPM state, the magnetization of aligned ferrofluid increased by a factor varying between 2 and 4 with respect to that in the randomly oriented state. The negative interaction energy obtained from the Curie-Weiss fit to the high temperature susceptibility in the SPM states as well as the SSG phase onset temperature determined from the linear magnetization curves were found to be rather insensitive to the anisotropy axis alignment. The low temperature aging behaviour, explored via "zero-field cooled magnetization" (ZFCM) relaxation measurements, however, show distinct difference in the aging dynamics in the anisotropy-axis aligned and randomly oriented SSG states.Comment: to appear in Journal of Physics D: Applied Physic

Electron quantum optics as quantum signal processing

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