24,533 research outputs found

    Phase separation in the vicinity of the surface of κ\kappa-(BEDT-TTF)2_2Cu[N(CN)2_2]Br by fast cooling

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    Partial suppression of superconductivity by fast cooling has been observed in the organic superconductor κ\kappa-(BEDT-TTF)2_2Cu[N(CN)2_2]Br by two means: a marked sample size effect on the magnetic susceptibility and direct imaging of insulating regions by scanning microregion infrared reflectance spectroscopy. Macroscopic insulating regions are found in the vicinity of the crystalline surface after fast cooling, with diameters of 50--100 μ\mum and depths of a few μ\mum. The very large in-plane penetration depth reported to date (\sim 24--100 μ\mum) can be explained by the existence of the insulating regions.Comment: Several rhetoric alternations to avoid misleadings. 6 pages, 3 figures. to be publihsed in Phys. Rev.

    Phonon engineering with superlattices: generalized nanomechanical potentials

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    Earlier implementations to simulate coherent wave propagation in one-dimensional potentials using acoustic phonons with gigahertz-terahertz frequencies were based on coupled nanoacoustic resonators. Here, we generalize the concept of adiabatic tuning of periodic superlattices for the implementation of effective one-dimensional potentials giving access to cases that cannot be realized by previously reported phonon engineering approaches, in particular the acoustic simulation of electrons and holes in a quantum well or a double well potential. In addition, the resulting structures are much more compact and hence experimentally feasible. We demonstrate that potential landscapes can be tailored with great versatility in these multilayered devices, apply this general method to the cases of parabolic, Morse and double-well potentials and study the resulting stationary phonon modes. The phonon cavities and potentials presented in this work could be probed by all-optical techniques like pump-probe coherent phonon generation and Brillouin scattering

    SpecPro: An Interactive IDL Program for Viewing and Analyzing Astronomical Spectra

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    We present an interactive IDL program for viewing and analyzing astronomical spectra in the context of modern imaging surveys. SpecPro's interactive design lets the user simultaneously view spectroscopic, photometric, and imaging data, allowing for rapid object classification and redshift determination. The spectroscopic redshift can be determined with automated cross-correlation against a variety of spectral templates or by overlaying common emission and absorption features on the 1-D and 2-D spectra. Stamp images as well as the spectral energy distribution (SED) of a source can be displayed with the interface, with the positions of prominent photometric features indicated on the SED plot. Results can be saved to file from within the interface. In this paper we discuss key program features and provide an overview of the required data formats.Comment: Accepted for publication in the Publications of the Astronomical Society of the Pacific (PASP) journal. Website: specpro.caltech.ed

    Infrared spectroscopy under multi-extreme conditions: Direct observation of pseudo gap formation and collapse in CeSb

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    Infrared reflectivity measurements of CeSb under multi-extreme conditions (low temperatures, high pressures and high magnetic fields) were performed. A pseudo gap structure, which originates from the magnetic band folding effect, responsible for the large enhancement in the electrical resistivity in the single-layered antiferromagnetic structure (AF-1 phase) was found at a pressure of 4 GPa and at temperatures of 35 - 50 K. The optical spectrum of the pseudo gap changes to that of a metallic structure with increasing magnetic field strength and increasing temperature. This change is the result of the magnetic phase transition from the AF-1 phase to other phases as a function of the magnetic field strength and temperature. This result is the first optical observation of the formation and collapse of a pseudo gap under multi-extreme conditions.Comment: 5 pages, 3 figures, accepted for publication in Phys. Rev.

    Stochastic delocalization of finite populations

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    Heterogeneities in environmental conditions often induce corresponding heterogeneities in the distribution of species. In the extreme case of a localized patch of increased growth rates, reproducing populations can become strongly concentrated at the patch despite the entropic tendency for population to distribute evenly. Several deterministic mathematical models have been used to characterize the conditions under which localized states can form, and how they break down due to convective driving forces. Here, we study the delocalization of a finite population in the presence of number fluctuations. We find that any finite population delocalizes on sufficiently long time scales. Depending on parameters, however, populations may remain localized for a very long time. The typical waiting time to delocalization increases exponentially with both population size and distance to the critical wind speed of the deterministic approximation. We augment these simulation results by a mathematical analysis that treats the reproduction and migration of individuals as branching random walks subject to global constraints. For a particular constraint, different from a fixed population size constraint, this model yields a solvable first moment equation. We find that this solvable model approximates very well the fixed population size model for large populations, but starts to deviate as population sizes are small. The analytical approach allows us to map out a phase diagram of the order parameter as a function of the two driving parameters, inverse population size and wind speed. Our results may be used to extend the analysis of delocalization transitions to different settings, such as the viral quasi-species scenario

    Cluster structures in Oxygen isotopes

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    Cluster structure of 16O,18O and 20O is investigated by the antisymmettrized molecular dynamics (AMD) plus generator coordinate method (GCM). We have found the K^{\pi}=02+_2^+ and 01_1^- rotational bands of 18O that have the prominent 14C+\alpha cluster structure. Clustering systematics becomes richer in 20O. We suggest the K^{\pi}=02+_2^+ band that is the mixture of the 12C+\alpha+4n and 14C+6He cluster structures, and the K^{\pi}=01_1^- band that has the 14C+6He cluster structure. The K^{\pi}=03+_3^+ and 02_2^- bands that have the prominent 16C+\alpha cluster structure are also found.Comment: 9pages, 9figure

    Superdeformation and clustering in 40^{40}Ca studied with Antisymmetrized Molecular Dynamics

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    Deformed states in 40^{40}Ca are investigated with a method of antisymmetrized molecular dynamics. Above the spherical ground state, rotational bands arise from a normal deformation and a superdeformation as well as an oblate deformation. The calculated energy spectra and E2E2 transition strengths in the superdeformed band reasonably agree to the experimental data of the superdeformed band starting from the 03+0^+_3 state at 5.213 MeV. By the analysis of single-particle orbits, it is found that the superdeformed state has particle-hole nature of an 8p8p-8h8h configuration. One of new findings is parity asymmetric structure with 12^{12}C+28^{28}Si-like clustering in the superdeformed band. We predict that 12^{12}C+28^{28}Si molecular bands may be built above the superdeformed band due to the excitation of inter-cluster motion. They are considered to be higher nodal states of the superdeformed state. We also suggest negative-parity bands caused by the parity asymmetric deformation.Comment: 13 figures, submitted to Phys. Rev.
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