Ref HAL: hal-01180430_v1
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The dynamics of glass-forming liquids is heterogeneous and displays growing spatial correlations upon cooling. Whether such behavior arises from heterogeneities in the local structure or more complex forms of amorphous order is a highly debated question. To clarify this issue, we study several model liquids within a coherent simulation framework based on the iso-configurational ensemble. We find that the correlation between the preferred local structure and the propensity of motion is pronounced in systems that deviate markedly from the mean-field picture of glassy dynamics and weak in models that adhere to it to a good extent. We conclude that the degree to which structural correlations affect the dynamics around the dynamic crossover is, in general, system-dependent.

Ref HAL: hal-01179792_v1
DOI: 10.1007/s00705-015-2515-y
WoS: 000361817600004
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5 Citations
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Several variants of the major ‘‘a’’ determinant of the HBsAg, the main target of HBV neutralization by antibodies, have been described. However, mutations out- side this region have not been as thoroughly investigated. During the genotyping of HBV from Tunisian patients with chronic hepatitis B, we identified a variant with a C69R substitution in the cytosolic loop of the S protein, resulting in a change in the hydrophobicity profile compared to the wild-type HBsAg. Wild-type and mutant HBsAgs were produced in Saccharomyces cerevisiae and recombinant proteins were tested for their ability to correctly self- assemble into virus-like particles (VLPs), and their ability to bind to HBs antibodies. The C69R substitution resulted in a decrease in binding to commercial anti-HBs antibod- ies, and although the variant appeared to assemble properly into VLPs, the average size of the particles was larger than that of the wild-type HBsAg. Prediction of the tertiary structure of the C69R mutant revealed a change in the first (aa 60-70) and the second loop (aa 110 to 120) compared to the wild-type protein. Furthermore, we showed by an isothermal titration calorimetry assay that the interaction between the wild-type HBsAg and the anti-HBs antibody was exothermic, whereas that with the mutant C69R was endothermic, indicating an effect on the binding affinity.

Résumé:

Spin noise spectroscopy (SNS) is an attractive optical technique, which in recent years has been widely used to probe the carrier spin relaxation in various semiconductors and heterostructures [1]. Typically SNS probes spontaneous spin fluctuations by off-resonant Faraday rotation. Spin noise spectra have to be equivalent to electron spin resonance spectra, by virtue of the fluctuation-dissipation theorem, and are quite interesting for quantum non-demolition measurements of either atomic or electronic spins [2]. Here we show that spin fluctuations of magnetic impurities in semiconductors can also be efficiently detected by SNS. This is demonstrated for manganese spins diluted in CdTe. Mn ions possess an electronic spin S=5/2, and a nuclear spin I=5/2. Thus one expects that the spin noise spectra will exhibit spectral signatures associated with the hyperfine interaction, and a dependence on the magnetic field direction dictated by the point-symmetry of the Mn ion in the lattice. This is illustrated in Figure 1, where contour plots of the spin noise spectra are shown for different magnetic field orientations in the (1-10) plane of the sample, q being the angle between the applied field and the [001] crystal axis. The spectra measured on bulk Cd0:999Mn0:001Te (Fig. 1b) exhibit many of the spectral features predicted within the spin hamiltonian approximation (Fig. 1a). Fig. 1c shows that quite good agreement between theory and experiment is obtained for a Mn spin coherence time T2 = 20 ns, which is the only fitting parameter. We will present our results on two CdMnTe quantum wells grown in coherent epitaxy on either CdTe or Cd0:96Zn0:04Te substrate. The first QW is almost lattice matched to the substrate and nearly unstrained, while the other is unmatched and strained. About 4106 Mn spins are detected in the spot size of 5 μm. We will show that, because of the hyperfine coupling between an electronic spin and a nuclear spin with the same value (5/2), below 15 mT Mn ions exhibit a Zeeman effect with an effective g-factor equal 1, rather than 2. The Mn spin noise spectra appear to be quite sensitive to the presence of local strains, and gives insights into the strain distribution in the QWs. Finally, we will discuss the possible spin relaxation mechanisms, which ultimately limit the Mn spin relaxation time. This work is supported by the French ANR research project SNS (Grant N° 2011-BS04-018 01).

Résumé:

Spin noise spectroscopy (SNS) is an attractive optical technique, which in recent years has been widely used to probe the carrier spin relaxation in various semiconductors and heterostructures [1]. Typically SNS probes spontaneous spin fluctuations by off-resonant Faraday rotation. Spin noise spectra have to be equivalent to electron spin resonance spectra, by virtue of the fluctuation-dissipation theorem, and are quite interesting for quantum non-demolition measurements of either atomic or electronic spins [2]. Here we show that spin fluctuations of magnetic impurities in semiconductors can also be efficiently detected by SNS. This is demonstrated for manganese spins diluted in CdTe. Mn ions possess an electronic spin S=5/2, and a nuclear spin I=5/2. Thus one expects that the spin noise spectra will exhibit spectral signatures associated with the hyperfine interaction, and a dependence on the magnetic field direction dictated by the point-symmetry of the Mn ion in the lattice. This is illustrated in Figure 1, where contour plots of the spin noise spectra are shown for different magnetic field orientations in the (1-10) plane of the sample, q being the angle between the applied field and the [001] crystal axis. The spectra measured on bulk Cd0:999Mn0:001Te (Fig. 1b) exhibit many of the spectral features predicted within the spin hamiltonian approximation (Fig. 1a). Fig. 1c shows that quite good agreement between theory and experiment is obtained for a Mn spin coherence time T2 = 20 ns, which is the only fitting parameter. We will present our results on two CdMnTe quantum wells grown in coherent epitaxy on either CdTe or Cd0:96Zn0:04Te substrate. The first QW is almost lattice matched to the substrate and nearly unstrained, while the other is unmatched and strained. About 4106 Mn spins are detected in the spot size of 5 μm. We will show that, because of the hyperfine coupling between an electronic spin and a nuclear spin with the same value (5/2), below 15 mT Mn ions exhibit a Zeeman effect with an effective g-factor equal 1, rather than 2. The Mn spin noise spectra appear to be quite sensitive to the presence of local strains, and gives insights into the strain distribution in the QWs. Finally, we will discuss the possible spin relaxation mechanisms, which ultimately limit the Mn spin relaxation time. This work is supported by the French ANR research project SNS (Grant N° 2011-BS04-018 01).

Ref HAL: hal-01179062_v1
Ref Arxiv: 1504.02649
DOI: 10.1103/PhysRevE.92.012309
WoS: 000357863500001
Ref. & Cit.: NASA ADS
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30 Citations
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Jamming is a geometric phase transition occurring in dense particle systems in the absence of temperature. We use computer simulations to analyse the effect of thermal fluctuations on several signatures of the transition. We show that scaling laws for bulk and shear moduli only become relevant when thermal fluctuations are extremely small, and propose their relative ratio as a quantitative signature of jamming criticality. Despite the nonequilibrium nature of the transition, we find that thermally induced fluctuations and mechanical responses obey equilibrium fluctuation-dissipation relations near jamming, provided the appropriate fluctuating component of the particle displacements is analysed. This shows that mechanical moduli can be directly measured from particle positions in mechanically unperturbed packings, and suggests that the definition of a "nonequilibrium index" is unnecessary for amorphous materials. We find that fluctuations of particle displacements are spatially correlated, and define a transverse and a longitudinal correlation lengthscales which both diverge as the jamming transition is approached. We analyse the frozen component of density fluctuations and find that it displays signatures of nearly-hyperuniform behaviour at large lengthscales. This demonstrates that hyperuniformity in jammed packings is unrelated to a vanishing compressibility and explains why it appears remarkably robust against temperature and density variations. Differently from jamming criticality, obstacles preventing the observation of hyperuniformity in colloidal systems do not originate from thermal fluctuations.

Commentaires: 16 pages, 8 figures; v2 accepted for publication in Phys. Rev. E. Réf Journal: Phys. Rev. E 92, 012309 (2015)

Ref HAL: hal-01178151_v1
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Recent results on probing of topological phases in Montpellier

Ref HAL: hal-01177136_v1
Ref Arxiv: 1506.07506
DOI: 10.1103/PhysRevD.92.074027
WoS: WOS:000363237400004
Ref. & Cit.: NASA ADS
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18 Citations
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Our recently developed variant of variationnally optimized perturbation (OPT), in particular consistently incorporating renormalization group properties (RGOPT), is adapted to the calculation of the QCD spectral density of the Dirac operator and the related chiral quark condensate $\langle \bar q q \rangle$ in the chiral limit, for $n_f=2$ and $n_f=3$ massless quarks. The results of successive sequences of approximations at two-, three-, and four-loop orders of this modified perturbation, exhibit a remarkable stability. We obtain $\langle \bar q q\rangle^{1/3}_{n_f=2}(2\, {\rm GeV}) = -(0.833-0.845) \bar\Lambda_2 $, and $ \langle\bar q q\rangle^{1/3}_{n_f=3}(2\, {\rm GeV}) = -(0.814-0.838) \bar\Lambda_3 $ where the range spanned by the first and second numbers (respectively four- and three-loop order results) defines our theoretical error, and $\bar\Lambda_{n_f}$ is the basic QCD scale in the $\overline{MS}$-scheme. We obtain a moderate suppression of the chiral condensate when going from $n_f=2$ to $n_f=3$. We compare these results with some other recent determinations from other nonperturbative methods (mainly lattice and spectral sum rules).

Commentaires: 20 pages, 1 figure