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Abraham, J., P. Abreu, M. Aglietta, C. Aguirre, D. Allard, I. Allekotte, J. Allen, P. Allison, J. Alvarez-Muniz, M. Ambrosio et al. "Observation of the suppression of the flux of cosmic rays above 4x10(19) eV." PHYSICAL REVIEW LETTERS 101, no. 6 (2008).
Abstract: The energy spectrum of cosmic rays above 2.5 x 10(18) eV, derived from 20 000 events recorded at the Pierre Auger Observatory, is described. The spectral index gamma of the particle flux, J proportional to E-gamma, at energies between 4 x 10(18) eV and 4 x 10(19) eV is 2.69 +/- 0.02(stat) +/- 0.06(syst), steepening to 4.2 +/- 0.4(stat) +/- 0: 06 (syst) at higher energies. The hypothesis of a single power law is rejected with a significance greater than 6 standard deviations. The data are consistent with the prediction by Greisen and by Zatsepin and Kuz'min.
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Abraham, J., P. Abreu, M. Aglietta, C. Aguirre, D. Allard, I. Allekotte, J. Allen, P. Allison, J. Alvarez-Muniz, M. Ambrosio et al. "Upper limit on the diffuse flux of ultrahigh energy tau neutrinos from the Pierre Auger Observatory." PHYSICAL REVIEW LETTERS 100, no. 21 (2008).
Abstract: The surface detector array of the Pierre Auger Observatory is sensitive to Earth-skimming tau neutrinos that interact in Earth's crust. Tau leptons from nu(tau) charged-current interactions can emerge and decay in the atmosphere to produce a nearly horizontal shower with a significant electromagnetic component. The data collected between 1 January 2004 and 31 August 2007 are used to place an upper limit on the diffuse flux of nu(tau) at EeV energies. Assuming an E-nu(-2) differential energy spectrum the limit set at 90% C. L. is E(nu)(2)dN(nu tau)/dE(nu) < 1: 3 x 10(-7) GeV cm(-2) s(-1) sr(-1) in the energy range 2 x 10(17) eV< E-nu < 2 x 10(19) eV.
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Rigal, L. B., D. C. Schmadel, H. D. Drew, B. Maiorov, E. Osquiguil, J. S. Preston, R. Hughes, and G. D. Gu. "Magneto-optical evidence for a gapped Fermi surface in underdoped YBa 2Cu3O6+x." Physical Review Letters 93, no. 13 (2004).
Abstract: An evidence presented that supports partial gapping of the Fermi surface by a measurement of the Hall frequency from high frequency magneto-optical measurements on underdoped YBa2Cu3O6+x (YBCO) was discussed. It was found that the Hall frequency was obtained independently of the unknown k-space dependence of the carrier scattering rates that complicated the dc Hall effect. It was observed that the frequency dependence of the Hall angle was Drude-like and indicated a quasielastic relaxation process for optimal and underdoped samples. The results show that there was an increase of the Hall frequency in the pseudogap state.
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Maiorov, B., A. V. Silhanek, F. De la Cruz, E. Osquiguil, A. Rydh, and Rapp. "Comment on “strong vortex liquid correlation from multiterminal measurements on untwinned YBa2Cu3O7-? single crystals” [2] (multiple letters)." Physical Review Letters 88, no. 13 (2002).
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Ridner, A., E. N. Martínez, and F. de la Cruz. "Surface-Temperature Determination in the Kapitza Problem." Physical Review Letters 35, no. 13 (1975): 855–858.
Abstract: It is shown that surface superconductivity can be used as a localized thermometer. Its application to the study of the thermal boundary resistance at a Pb-4He interface provides the first experimental evidence for the existence of a rapid temperature variation within microscopic distances from the surface.
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Fullerton, E. E., D. M. Kelly, J. Guimpel, I. K. Schuller, and Y. Bruynseraede. "Roughness and giant magnetoresistance in Fe/Cr superlattices." Physical Review Letters 68, no. 6 (1992): 859.
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Safar, H., P. L. Gammel, D. A. Huse, S. N. Majumdar, L. F. Schneemeyer, D. J. Bishop, D. Lopez, G. L. Nieva, and F. de la Cruz. "Observation of a nonlocal conductivity in the mixed state of YBa2Cu3O7-d: Experimental evidence for a vortex line liquid." Physical Review Letters 72, no. 8 (1994): 1272.
Abstract: We report on transport measurements in the mixed state of YBa2Cu3O7 single crystals using the dc flux transformer geometry. In the vortex fluid regime we have observed the onset of a nonlocal conductivity. At lower temperatures, close to but above the phase transition temperature the vortices become effectively three dimensional in character. This is in sharp contrast to recent flux transformer experiments on Bi2Sr2CaCu2O which have failed to see a nonlocal conductivity, confirming the two-dimensional character at high temperatures of the vortices in that system. These observations suggest that in a finite temperature interval, the vortex state in YBa2Cu3O7 is a line liquid.
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Griessen, R., Wen Hai-Hu, A. J. J. Van Dalen, B. Dam, J. Rector, H. G. Schnack, S. Libbrecht, E. Osquiguil, and Y. Bruynseraede. "Evidence for mean free path fluctuation induced pinning in YBa2Cu3O7 and YBa2Cu4O8 films." Physical Review Letters 72, no. 12 (1994): 1910–1913.
Abstract: The critical current jc and the pinning energy Uc have been determined for three types of yttrium-based superconducting films from current js and dynamic relaxation Q=d lnjs/d ln(dB/dt) data by means of the generalized inversion scheme. For B<2 T and T<80 K the temperature dependence of jc and Uc for all films is found to be in excellent agreement with a model of single vortices pinned by randomly distributed weak pinning centers via spatial fluctuations of the charge carrier mean free path. Pinning due to spatial fluctuations of Tc is not observed.
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Welp, U., M. Grimsditch, S. Fleshler, W. Nessler, J. Downey, G. W. Crabtree, and J. Guimpel. "Effect of uniaxial stress on the superconducting transition in YBa{2}Cu{3}O_{7}." Physical Review Letters 69, no. 14 (1992): 2130.
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Grigera, S. A., E. Morre, E. Osquiguil, C. Balseiro, G. Nieva, and F. de la Cruz. "Bose-glass phase in twinned YBa2Cu3O7-delta." PHYSICAL REVIEW LETTERS 81, no. 11 (1998): 2348–2351.
Abstract: Using an extensive scaling analysis of the transport properties in twinned YBa2Cu3O7-delta crystals we have experimentally found the predicted change in the universality class of the Bose-glass to liquid transition when the magnetic field is applied at small angles away from the direction of the correlated defects. The new dynamical critical exponent is s' = 1.1 +/- 0.3.
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