2,142 research outputs found

    Anomalous thermopower and Nernst effect in CeCoIn5\rm CeCoIn_5: entropy-current loss in precursor state

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    The heavy-electron superconductor CeCoIn5_5 exhibits a puzzling precursor state above its superconducting critical temperature at TcT_c = 2.3 K. The thermopower and Nernst signal are anomalous. Below 15 K, the entropy current of the electrons undergoes a steep decrease reaching \sim0 at TcT_c. Concurrently, the off-diagonal thermoelectric current αxy\alpha_{xy} is enhanced. The delicate sensitivity of the zero-entropy state to field implies phase coherence over large distances. The prominent anomalies in the thermoelectric current contrast with the relatively weak effects in the resistivity and magnetization.Comment: 5 figures, 4 page

    The Lorenz number in CeCoIn5_5 inferred from the thermal and charge Hall currents

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    The thermal Hall conductivity κxy\kappa_{xy} and Hall conductivity σxy\sigma_{xy} in CeCoIn5_5 are used to determine the Lorenz number LH{\cal L}_H at low temperature TT. This enables the separation of the observed thermal conductivity into its electronic and non-electronic parts. We uncover evidence for a charge-neutral, field-dependent thermal conductivity, which we identify with spin excitations. At low TT, these excitations dominate the scattering of charge carriers. We show that suppression of the spin excitations in high fields leads to a steep enhancement of the electron mean-free-path, which leads to an interesting scaling relation between the magnetoresistance, thermal conductivity and σxy\sigma_{xy}.Comment: 6 pages, 7 figures Intro para slightly lengthened. Added 2 new re

    Evidence for electron-phonon interaction in Fe1x_{1-x}Mx_{x}Sb2_{2} (M=Co, Cr) single crystals

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    We have measured polarized Raman scattering spectra of the Fe1x_{1-x}Cox_{x}Sb2_{2} and Fe1x_{1-x}Crx_{x}Sb2_{2} (0x\leq x\leq 0.5) single crystals in the temperature range between 15 K and 300 K. The highest energy B1gB_{1g} symmetry mode shows significant line asymmetry due to phonon mode coupling width electronic background. The coupling constant achieves the highest value at about 40 K and after that it remains temperature independent. Origin of additional mode broadening is pure anharmonic. Below 40 K the coupling is drastically reduced, in agreement with transport properties measurements. Alloying of FeSb2_2 with Co and Cr produces the B1g_{1g} mode narrowing, i.e. weakening of the electron-phonon interaction. In the case of Ag_{g} symmetry modes we have found a significant mode mixing

    On the role of fine-sand dune dynamics in controlling water depth changes in Rio Parapeti, Serrania Borebigua (Southern sub-Andean zone of Bolivia)

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    The role of the fine-dune sand dynamics in controlling the natural regeneration of the upper layer of a riverbed used for filtration is studied at the Choreti test reach of Rio Parapeti, in the Southern sub-Andean zone of Bolivia. Local production of drinking water relies on Riverbed Filtration, the delivery of which depends on the river water depth and the riverbed permeability. There is a strong, natural, declamation process of the upper layer maintained by dune bed-forms migrating downstream. It is thus essential to understand and represent local water depth changes as a function of the incoming discharge. We show the vortex-drag model can be used to correctly calculate the stream velocity in natural environment. Then we study the sand dunes characteristic (wavelength and celerity) in the Rio Parapeti. Because of the shallow-flow configuration the dominant dune length can be easily extracted from satellite images taken at various dates. We also show that it is more than likely that dune movement can be followed by the simple deployment of a pressure probe into the water under stable discharge condition, even if further data and investigation are necessary to confirm this

    Comment on "Spatial optical solitons in highly nonlocal media" and related papers

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    In a recent paper [A. Alberucci, C. Jisha, N. Smyth, and G. Assanto, Phys. Rev. A 91, 013841 (2015)], Alberucci et al. have studied the propagation of bright spatial solitary waves in highly nonlocal media. We find that the main results in that and related papers, concerning soliton shape and dynamics, based on the accessible soliton (AS) approximation, are incorrect; the correct results have already been published by others. These and other inconsistencies in the paper follow from the problems in applying the AS approximation in earlier papers by the group that propagated to the later papers. The accessible soliton theory cannot describe accurately the features and dynamics of solitons in highly nonlocal media.Comment: 2 page

    Topological Quantum Computing with Only One Mobile Quasiparticle

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    In a topological quantum computer, universal quantum computation is performed by dragging quasiparticle excitations of certain two dimensional systems around each other to form braids of their world lines in 2+1 dimensional space-time. In this paper we show that any such quantum computation that can be done by braiding nn identical quasiparticles can also be done by moving a single quasiparticle around n-1 other identical quasiparticles whose positions remain fixed.Comment: 4 pages, 5 figure

    Kondo Insulator description of spin state transition in FeSb2

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    The thermal expansion and heat capacity of FeSb2 at ambient pressure agrees with a picture of a temperature induced spin state transition within the Fe t_{2g} multiplet. However, high pressure powder diffraction data show no sign of a structural phase transition up to 7GPa. A bulk modulus B=84(3)GPa has been extracted and the temperature dependence of the Gruneisen parameter has been determined. We discuss here the relevance of a Kondo insulator description for this material.Comment: Physical Review B in press (2005
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