Physical Review Letters

Kanigel, A; Keren, A; Patlagan, L; Chashka, K. B; King, P. B

doi: 10.1103/PhysRevLett.92.257007pmid: 15245055

Using the transverse field muon spin relaxation technique, we measure the temperature dependence of the magnetic field penetration depth λ , in the Na x CoO 2 · y H 2 O system. We find that λ , which is determined by the superfluid density n s and the effective mass m * , is very small and on the edge of the TF- μ SR sensitivity. Nevertheless, the results indicate that this system obeys the Uemura relation. By comparing λ with the normal state electron density, we conclude that m * of the superconductivity carrier is 70 times larger than the mass of bare electrons. Finally, the order parameter in this system cannot be described by a complete gap over the entire Fermi surface.

Lam, Chi-Hang

doi: 10.1103/PhysRevLett.92.254503pmid: 15245015

We suggest that the dynamics of stable viscous invasion fronts in porous media depends on the volume capacitance of the media. At high volume capacitance, our network simulations provide numerical evidence of a scaling relation between the front width and its velocity. In the low volume capacitance regime, we derive a new effective scaling supported by network simulations and that is in agreement with previous experiments on imbibition in paper and collections of glass beads.

Mazumdar, Anupam ; Pérez-Lorenzana, Abdel

doi: 10.1103/PhysRevLett.92.251301pmid: 15244992

We bring together some known ingredients beyond the standard model physics that can explain the hot big bang model with the observed baryon asymmetry and also the fluctuations in the cosmic microwave background radiation with a minimal set of assumptions. We propose an interesting scenario where the inflaton energy density is dumped into an infinitely large extra dimension. Instead of the inflaton it is the right handed sneutrino condensate, which is acquiring a nonzero vacuum expectation value during inflation, whose fluctuations are responsible for the density perturbations seen in the cosmic microwave background radiation with a spectral index n s ≈ 1 . The decay of the condensate is explaining the reheating of the Universe with a temperature, T r h ≤ 10 9 GeV , and the baryon asymmetry of order one part in 10 10 with no baryon-isocurvature fluctuations.

Pfeiffer, M; Ahrens, J; Annand, J. R; Beck, R. R; Caselotti, G. R; Cherepnya, S. R; Föhl, K. R; Fog, L. S; Hornidge, D. S; Janssen, S. S; Kashevarov, V. S; Kondratiev, R. S; Kotulla, M. S; Krusche, B. S; McGeorge, J. C; MacGregor, I. J; Mengel, K. J;

Csáthy, G. A; Tsui, D. C; Pfeiffer, L. N; West, K. W

doi: 10.1103/PhysRevLett.92.256804pmid: 15245047

We have measured the magnetoresistance of a very low density and extremely high quality two-dimensional hole system. With increasing magnetic field applied perpendicularly to the sample we observe the sequence of insulating, ν = 1 / 3 fractional quantum Hall liquid, and insulating phases. In both of the insulating phases in the vicinity of the ν = 1 / 3 filling the magnetoresistance has an unexpected oscillatory behavior with the magnetic field. These oscillations are not of the Shubnikov–de Haas type and cannot be explained by spin effects. They are most likely the consequence of the formation of a new electronic phase which is intermediate between the correlated Hall liquid and a disorder pinned solid.

Strässle, Th; Juranyi, F; Schneider, M; Janssen, S; Furrer, A

doi: 10.1103/PhysRevLett.92.257202pmid: 15245057

The origin of higher-order exchange interactions in localized S -state systems has been the subject of intensive investigations in the past. In particular, it has been suggested that a biquadratic exchange term may arise from the magnetoelastic energy. Here we report on the pressure and temperature dependence of the excitation spectra of magnetic Mn 2 + dimers in CsMn 0.28 Mg 0.72 Br 3 probed by inelastic neutron scattering. Biquadratic exchange and a strong distance dependence of the bilinear exchange are observed. It is shown that the mechanism of local exchange striction may explain the occurrence of biquadratic exchange in accordance with the elastic properties of the compound.

Massa, Michael V; Dalnoki-Veress, Kari V

doi: 10.1103/PhysRevLett.92.255509pmid: 15245030

We present a study of homogeneous nucleation in polymer crystallization. Crystal nucleation is observed within discrete droplets of poly(ethylene oxide) that are formed by the dewetting of a thin film. The samples provide an ensemble of impurity-free droplets, with length scales that can easily be measured. Droplet crystallization is found in two distinct temperature regimes corresponding to homogeneous and heterogeneous nucleation. Here we focus on homogeneous nucleation and show that the nucleation rate scales with the volume of the crystallizable domain, indicating that we are observing homogeneous nucleation in the bulk of the droplets. In addition, the dependence of the nucleation rate on temperature is consistent with classical nucleation theory.

Prévot, G; Croset, B

doi: 10.1103/PhysRevLett.92.256104pmid: 15245038

We expose a new analytical method for computing elastic displacements and interactions due to steps on vicinal surfaces. The model of a “buried dipole” allows us to take into account the specific geometry of the step while performing anisotropic linear elasticity calculations. The displacements found show a remarkable agreement with molecular dynamics simulations for Cu and Pt (001) and (111) vicinals. The interaction energy between steps strongly depends on the dipole direction.

Hsiang, Jen-Tsung ; Ford, L. H

doi: 10.1103/PhysRevLett.92.250402pmid: 15244987

The effect of time-varying electromagnetic fields on electron coherence is investigated. A sinusoidal electromagnetic field produces a time-varying Aharonov-Bohm phase. In a measurement of the interference pattern which averages over this phase, the effect is a loss of contrast. This is effectively a form of decoherence. We calculate the magnitude of this effect for various electromagnetic field configurations. The result seems to be sufficiently large to be observable.

Hilles, Hani M; Ortega, Francisco M; Rubio, Ramón G; Monroy, Francisco G

doi: 10.1103/PhysRevLett.92.255503pmid: 15245024

We have carried out an experimental study on the mechanical relaxation of Langmuir films of a glass-forming polymer, poly-(4-hydroxystyrene), a good example of a two-dimensional system made of condensed polymer coils (at poor-solvent conditions). This study allows us to explore the response functions of the film and the temperature and density dependencies of the relaxation time. The dynamical properties show glasslike features (non-Debye mechanical response and non-Arrhenius relaxation times) reconcilable within the frame of the mode-coupling model.