697 results on '"Vieira S"'
Search Results
2. Author Correction: Carbon stocks in central African forests enhanced by elephant disturbance (Nature Geoscience, (2019), 12, 9, (725-729), 10.1038/s41561-019-0395-6)
- Author
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Berzaghi, F, Longo, M, Ciais, P, Blake, S, Bretagnolle, F, Vieira, S, Scaranello, M, Scarascia-Mugnozza, G, and Doughty, CE
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Meteorology & Atmospheric Sciences - Abstract
In the version of this Article originally published, the first sentence of the Acknowledgements “We would like to thank D. Papale, M. Zapparoli, L. Portoghesi, M. di Porcia e Brugnera, and H. Verbeeck for feedback that helped improve the manuscript.” should have been “We would like to thank: F. Berzaghi's PhD thesis committee: D. Papale, M. Zapparoli and L. Portoghesi; A. Swann and S. Wasser for their conception of this idea and their mentorship during the initial work on the project; and M. di Porcia e Brugnera and H. Verbeeck for feedback that helped improve the manuscript.” This has now been amended.
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- 2019
3. Tilted vortex cores and superconducting gap anisotropy in 2H-NbSe2
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Galvis, J. A., Herrera, E., Berthod, C., Vieira, S., Guillamon, I., and Suderow, H.
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Condensed Matter - Superconductivity - Abstract
Superconducting vortex cores have been extensively studied for magnetic fields applied perpendicular to the surface by mapping the density of states (DOS) through Scanning Tunneling Microscopy (STM). Vortex core shapes are often linked to the superconducting gap anisotropy---quasiparticle states inside vortex cores extend along directions where the superconducting gap is smallest. The superconductor 2H-NbSe$_2$ crystallizes in a hexagonal structure and vortices give DOS maps with a sixfold star shape for magnetic fields perpendicular to the surface and the hexagonal plane. This has been associated to a hexagonal gap anisotropy located on quasi two-dimensional Fermi surface tubes oriented along the $c$ axis. The gap anisotropy in another, three-dimensional, pocket is unknown. However, the latter dominates the STM tunneling conductance. Here we measure DOS in magnetic fields parallel to the surface and perpendicular to the $c$ axis. We find patterns of stripes due to in-plane vortex cores running nearly parallel to the surface. The patterns change with the in-plane direction of the magnetic field, suggesting that the sixfold gap anisotropy is present over the whole Fermi surface. Due to a slight misalignment between the vector of the magnetic field and the surface, our images also show outgoing vortices. Their shape is successfully compared to detailed calculations of vortex cores in tilted fields. Their features merge with the patterns due to in plane vortices, suggesting that they exit at an angle with the surface. Measuring the DOS of vortex cores in highly tilted magnetic fields with STM can thus be used to study the superconducting gap structure.
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- 2017
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4. Subsurface bending and reorientation of tilted vortex lattices in the bulk due to Coulomb-like repulsion at the surface
- Author
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Herrera, E., Guillamon, I., Galvis, J. A., Correa, A., Fente, A., Vieira, S., Suderow, H., Martinovich, A. Yu., and Kogan, V. G.
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Condensed Matter - Superconductivity - Abstract
We study vortex lattices (VLs) in superconducting weak-pinning platelet-like crystals of $\beta$-Bi$_{2}$Pd in tilted fields with a Scanning Tunneling Microscope. We show that vortices exit the sample perpendicular to the surface and are thus bent beneath the surface. The structure and orientation of tilted VL in the bulk are, for large tilt angles, strongly affected by Coulomb-type intervortex repulsion at the surface due to stray fields.
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- 2017
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5. Strong enhancement of superconductivity at high pressures within the charge-density-wave states of 2H-TaS 2 and 2H-TaSe 2
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Freitas, D. C., Rodiere, P, Osorio, M. R., Navarro-Moratalla, E, Nemes, N. M., Tissen, V. G., Cario, L, Coronado, E, García-Hernández, M, Vieira, S, Núñez-Regueiro, M, and Suderow, H
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Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
We present measurements of the superconducting and charge density wave critical temperatures (Tc and TCDW) as a function of pressure in the transition metal dichalchogenides 2H-TaSe2 and 2H-TaS2. Resistance and susceptibility measurements show that Tc increases from temperatures below 1 K up to 8.5 K at 9.5 GPa in 2H-TaS2 and 8.2 K at 23 GPa in 2H-TaSe2. We observe a kink in the pressure dependence of TCDW at about 4 GPa that we attribute to the lock-in transition from incommensurate CDW to commensurate CDW. Above this pressure, the commensurate TCDW slowly decreases coexisting with superconductivity within our full pressure range., Comment: Published in Phys. Rev B 93, 184512 (2016)
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- 2016
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6. Positive feedbacks and alternative stable states in forest leaf types
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Zou, Y., Zohner, C., Averill, C., Ma, H., Merder, J., Berdugo, M., Bialic-Murphy, L., Mo, L., Brun, P., Zimmermann, N., Liang, J., de-Miguel, S., Nabuurs, G.-J., Reich, P., Niinements, U., Dahlgren, J., Kändler, G., Ratcliffe, S., Ruiz-Benito, P., de Zavala, M., Abegg, M., Adou Yao, Y., Alberti, G., Almeyda Zambrano, A., Alvarado, B., Alvarez-Dávila, E., Alvarez-Loayza, P., Alves, L., Ammer, C., Antón-Fernández, C., Araujo-Murakami, A., Arroyo, L., Avitabile, V., Aymard, G., Baker, T., Bałazy, R., Banki, O., Barroso, J., Bastian, M., Bastin, J.-F., Birigazzi, L., Birnbaum, P., Bitariho, R., Boeckx, P., Bongers, F., Bouriaud, O., Brancalion, P., Brandl, S., Brearley, F., Brienen, R., Broadbent, E., Bruelheide, H., Bussotti, F., Gatti, R., César, R., Cesljar, G., Chazdon, R., Chen, H., Chisholm, C., Cho, H., Cienciala, E., Clark, C., Clark, D., Colletta, G., Coomes, D., Valverde, F., Corral-Rivas, J., Crim, P., Cumming, J., Dayanandan, S., de Gasper, A., Decuyper, M., Derroire, G., DeVries, B., Djordjevic, I., Dolezal, J., Dourdain, A., Obiang, N., Enquist, B., Eyre, T., Fandohan, A., Fayle, T., Feldpausch, T., Ferreira, L., Finér, L., Fischer, M., Fletcher, C., Fridman, J., Frizzera, L., Gamarra, J., Gianelle, D., Glick, H., Harris, D., Hector, A., Hemp, A., Hengeveld, G., Hérault, B., Herbohn, J., Herold, M., Hillers, A., Honorio Coronado, E., Hui, C., Ibanez, T., Iêda, A., Imai, N., Jagodziński, A., Jaroszewicz, B., Johannsen, V., Joly, C., Jucker, T., Jung, I., Karminov, V., Kartawinata, K., Kearsley, E., Kenfack, D., Kennard, D., Kepfer-Rojas, S., Keppel, G., Khan, M., Killeen, T., Kim, H., Kitayama, K., Köhl, M., Korjus, H., Kraxner, F., Laarmann, D., Lang, M., Lewis, S., Lu, H., Lukina, N., Maitner, B., Malhi, Y., Marcon, E., Marimon, B., Marimon-Junior, B., Marshall, A., Martin, E., Kucher, D., Meave, J., Melo-Cruz, O., Mendoza, C., Merow, C., Mendoza, A., Moreno, V., Mukul, S., Mundhenk, P., Nava-Miranda, M., Neill, D., Neldner, V., Nevenic, R., Ngugi, M., Niklaus, P., Oleksyn, J., Ontikov, P., Ortiz-Malavasi, E., Pan, Y., Paquette, A., Parada-Gutierrez, A., Parfenova, E., Park, M., Parren, M., Parthasarathy, N., Peri, P., Pfautsch, S., Phillips, O., Picard, N., Piedade, M., Piotto, D., Pitman, N., Polo, I., Poorter, L., Poulsen, A., Poulsen, J., Pretzsch, H., Arevalo, F., Restrepo-Correa, Z., Rodeghiero, M., Rolim, S., Roopsind, A., Rovero, F., Rutishauser, E., Saikia, P., Salas-Eljatib, C., Saner, P., Schall, P., Schelhaas, M., Shchepashchenko, D., Scherer-Lorenzen, M., Schmid, B., Schöngart, J., Searle, E., Seben, V., Serra-Diaz, J., Sheil, D., Shvidenko, A., Silva-Espejo, J., Silveira, M., Singh, J., Sist, P., Slik, F., Sonké, B., Souza, A., Miscicki, S., Stereńczak, K., Svenning, J., Svoboda, M., Swanepoel, B., Targhetta, N., Tchebakova, N., ter Steege, H., Thomas, R., Tikhonova, E., Umunay, P., Usoltsev, V., Valencia, R., Valladares, F., van der Plas, F., Van Do, T., van Nuland, M., Vasquez, R., Verbeeck, H., Viana, H., Vibrans, A., Vieira, S., von Gadow, K., Wang, H., Watson, J., Werner, G., Westerlund, B., Wiser, S., Wittmann, F., Woell, H., Wortel, V., Zagt, R., Zawiła-Niedźwiecki, T., Zhang, C., Zhao, X., Zhou, M., Zhu, Z., Zo-Bi, I., Crowther, T., Zou, Y., Zohner, C., Averill, C., Ma, H., Merder, J., Berdugo, M., Bialic-Murphy, L., Mo, L., Brun, P., Zimmermann, N., Liang, J., de-Miguel, S., Nabuurs, G.-J., Reich, P., Niinements, U., Dahlgren, J., Kändler, G., Ratcliffe, S., Ruiz-Benito, P., de Zavala, M., Abegg, M., Adou Yao, Y., Alberti, G., Almeyda Zambrano, A., Alvarado, B., Alvarez-Dávila, E., Alvarez-Loayza, P., Alves, L., Ammer, C., Antón-Fernández, C., Araujo-Murakami, A., Arroyo, L., Avitabile, V., Aymard, G., Baker, T., Bałazy, R., Banki, O., Barroso, J., Bastian, M., Bastin, J.-F., Birigazzi, L., Birnbaum, P., Bitariho, R., Boeckx, P., Bongers, F., Bouriaud, O., Brancalion, P., Brandl, S., Brearley, F., Brienen, R., Broadbent, E., Bruelheide, H., Bussotti, F., Gatti, R., César, R., Cesljar, G., Chazdon, R., Chen, H., Chisholm, C., Cho, H., Cienciala, E., Clark, C., Clark, D., Colletta, G., Coomes, D., Valverde, F., Corral-Rivas, J., Crim, P., Cumming, J., Dayanandan, S., de Gasper, A., Decuyper, M., Derroire, G., DeVries, B., Djordjevic, I., Dolezal, J., Dourdain, A., Obiang, N., Enquist, B., Eyre, T., Fandohan, A., Fayle, T., Feldpausch, T., Ferreira, L., Finér, L., Fischer, M., Fletcher, C., Fridman, J., Frizzera, L., Gamarra, J., Gianelle, D., Glick, H., Harris, D., Hector, A., Hemp, A., Hengeveld, G., Hérault, B., Herbohn, J., Herold, M., Hillers, A., Honorio Coronado, E., Hui, C., Ibanez, T., Iêda, A., Imai, N., Jagodziński, A., Jaroszewicz, B., Johannsen, V., Joly, C., Jucker, T., Jung, I., Karminov, V., Kartawinata, K., Kearsley, E., Kenfack, D., Kennard, D., Kepfer-Rojas, S., Keppel, G., Khan, M., Killeen, T., Kim, H., Kitayama, K., Köhl, M., Korjus, H., Kraxner, F., Laarmann, D., Lang, M., Lewis, S., Lu, H., Lukina, N., Maitner, B., Malhi, Y., Marcon, E., Marimon, B., Marimon-Junior, B., Marshall, A., Martin, E., Kucher, D., Meave, J., Melo-Cruz, O., Mendoza, C., Merow, C., Mendoza, A., Moreno, V., Mukul, S., Mundhenk, P., Nava-Miranda, M., Neill, D., Neldner, V., Nevenic, R., Ngugi, M., Niklaus, P., Oleksyn, J., Ontikov, P., Ortiz-Malavasi, E., Pan, Y., Paquette, A., Parada-Gutierrez, A., Parfenova, E., Park, M., Parren, M., Parthasarathy, N., Peri, P., Pfautsch, S., Phillips, O., Picard, N., Piedade, M., Piotto, D., Pitman, N., Polo, I., Poorter, L., Poulsen, A., Poulsen, J., Pretzsch, H., Arevalo, F., Restrepo-Correa, Z., Rodeghiero, M., Rolim, S., Roopsind, A., Rovero, F., Rutishauser, E., Saikia, P., Salas-Eljatib, C., Saner, P., Schall, P., Schelhaas, M., Shchepashchenko, D., Scherer-Lorenzen, M., Schmid, B., Schöngart, J., Searle, E., Seben, V., Serra-Diaz, J., Sheil, D., Shvidenko, A., Silva-Espejo, J., Silveira, M., Singh, J., Sist, P., Slik, F., Sonké, B., Souza, A., Miscicki, S., Stereńczak, K., Svenning, J., Svoboda, M., Swanepoel, B., Targhetta, N., Tchebakova, N., ter Steege, H., Thomas, R., Tikhonova, E., Umunay, P., Usoltsev, V., Valencia, R., Valladares, F., van der Plas, F., Van Do, T., van Nuland, M., Vasquez, R., Verbeeck, H., Viana, H., Vibrans, A., Vieira, S., von Gadow, K., Wang, H., Watson, J., Werner, G., Westerlund, B., Wiser, S., Wittmann, F., Woell, H., Wortel, V., Zagt, R., Zawiła-Niedźwiecki, T., Zhang, C., Zhao, X., Zhou, M., Zhu, Z., Zo-Bi, I., and Crowther, T.
- Abstract
The emergence of alternative stable states in forest systems has significant implications for the functioning and structure of the terrestrial biosphere, yet empirical evidence remains scarce. Here, we combine global forest biodiversity observations and simulations to test for alternative stable states in the presence of evergreen and deciduous forest types. We reveal a bimodal distribution of forest leaf types across temperate regions of the Northern Hemisphere that cannot be explained by the environment alone, suggesting signatures of alternative forest states. Moreover, we empirically demonstrate the existence of positive feedbacks in tree growth, recruitment and mortality, with trees having 4–43% higher growth rates, 14–17% higher survival rates and 4–7 times higher recruitment rates when they are surrounded by trees of their own leaf type. Simulations show that the observed positive feedbacks are necessary and sufficient to generate alternative forest states, which also lead to dependency on history (hysteresis) during ecosystem transition from evergreen to deciduous forests and vice versa. We identify hotspots of bistable forest types in evergreen-deciduous ecotones, which are likely driven by soil-related positive feedbacks. These findings are integral to predicting the distribution of forest biomes, and aid to our understanding of biodiversity, carbon turnover, and terrestrial climate feedbacks.
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- 2024
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7. Stellar parameters for stars of the CoRoT exoplanet field
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Cortés, C., Maciel, S. C., Vieira, S., Lopes, C. E. Ferreira, Leão, I. C., de Oliveira, G. P., Correia, C., Martins, B. L. Canto, Catelan, M., and De Medeiros, J. R.
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Astrophysics - Solar and Stellar Astrophysics - Abstract
Aims:To support the computation and evolutionary interpretation of periods associated with the rotational modulation, oscillations, and variability of stars located in the CoRoT fields, we are conducting a spectroscopic survey for stars located in the fields already observed by the satellite. These observations allow us to compute physical and chemical parameters for our stellar sample. Method: Using spectroscopic observations obtained with UVES/VLT and Hydra/Blanco, and based on standard analysis techniques, we computed physical and chemical parameters ($T_{\rm{eff}}$, $\log \,(g)$, $\rm{[Fe/H]}$, $v_{\rm{mic}}$, $v_{\rm{rad}}$, $v \sin \,(i)$, and $A(\rm{Li})$) for a large sample of CoRoT targets. Results: We provide physical and chemical parameters for a sample comprised of 138 CoRoT targets. Our analysis shows the stars in our sample are located in different evolutionary stages, ranging from the main sequence to the red giant branch, and range in spectral type from F to K. The physical and chemical properties for the stellar sample are in agreement with typical values reported for FGK stars. However, we report three stars presenting abnormal lithium behavior in the CoRoT fields. These parameters allow us to properly characterize the intrinsic properties of the stars in these fields. Our results reveal important differences in the distributions of metallicity, $T_{\rm eff}$, and evolutionary status for stars belonging to different CoRoT fields, in agreement with results obtained independently from ground-based photometric surveys. Conclusions: Our spectroscopic catalog, by providing much-needed spectroscopic information for a large sample of CoRoT targets, will be of key importance for the successful accomplishment of several different programs related to the CoRoT mission, thus it will help further boost the scientific return associated with this space mission., Comment: 43 pages, 17 figures, accepted for publication in A&A
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- 2015
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8. Magnetic field dependence of the density of states in the multiband superconductor $\beta$-Bi$_2$Pd
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Herrera, E., Guillamon, I., Galvis, J. A., Correa, A., Fente, A., Luccas, R. F., Mompean, F. J., Garcia-Hernandez, M., Vieira, S., Brison, J. P., and Suderow, H.
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Condensed Matter - Superconductivity - Abstract
We present very low temperature scanning tunneling microscopy (STM) experiments on single crystalline samples of the superconductor $\beta$-Bi$_2$Pd. We find a single fully isotropic superconducting gap. However, the magnetic field dependence of the intervortex density of states is higher than the one expected in a single gap superconductor, and the hexagonal vortex lattice is locked to the square atomic lattice. Such increase in the intervortex density of states and vortex lattice locking have been found in superconductors with multiple superconducting gaps and anisotropic Fermi surfaces. We compare the upper critical field $H_{c2}(T)$ obtained in our sample with previous measurements and explain available data within multiband supercondutivity. We propose that $\beta$-Bi$_2$Pd is a single gap multiband superconductor. We anticipate that single gap multiband superconductivity can occur in other compounds with complex Fermi surfaces., Comment: 8 pages, 7 figures
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- 2015
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9. Evaluation of the antimicrobial activity of Eucalyptus radiata essential oil against Escherichia coli strains isolated from meat products
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Santos, B., primary, Farias, J. H. A., additional, Simões, M. M., additional, Medeiros, M. A. A., additional, Alves, M. S., additional, Diniz, A. F., additional, Soares, A. P. O., additional, Cavalcante, A. P. T. M., additional, Silva, B. J. N., additional, Almeida, J. C. S., additional, Lemos, J. O., additional, Rocha, L. E. S., additional, Santos, L. C., additional, Azevedo, M. L. G., additional, Vieira, S. W. F., additional, Araújo, V. E., additional, and Oliveira Filho, A. A., additional
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- 2024
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10. Enhancement of long range correlations in a 2D vortex lattice by incommensurate 1D disorder potential
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Guillamon, I., Cordoba, R., Sese, J., De Teresa, J. M., Ibarra, M. R., Vieira, S., and Suderow, H.
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Condensed Matter - Superconductivity - Abstract
Long range correlations in two-dimensional (2D) systems are significantly altered by disorder potentials. Theory has predicted the existence of disorder induced phenomena such as Anderson localization and the emergence of novel glass and insulating phases as the Bose glass. More recently, it has been shown that disorder breaking the 2D continuous symmetry, such as a one dimensional (1D) modulation, can enhance long range correlations. Experimentally, developments in quantum gases have allowed the observation of a wealth of phenomena induced by the competition between interaction and disorder. However, there are no experiments exploring the effect of symmetry-breaking disorder. Here, we create a 2D vortex lattice at 0.1 K in a superconducting thin film with a well-defined 1D thickness modulation and track the field induced modification using scanning tunneling microscopy. We find that the 1D modulation becomes incommensurate to the vortex lattice and drives an order-disorder transition, behaving as a scale-invariant disorder potential. We show that the transition occurs in two steps and is mediated by the proliferation of topological defects. We find that critical exponents determining the loss of positional and orientational order are far above theoretical expectations for scale-invariant disorder and follow instead the critical behaviour which describes dislocation unbinding melting. Our data show for the first time that randomness disorders a 2D crystal, and evidence enhanced long range correlations in presence of a 1D modulation demonstrating the transformation induced by symmetry breaking disorder in interactions and the critical behaviour of the transition., Comment: 7 pages, 3 figures and supplementary information (11 pages, 9 figures)
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- 2014
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11. Zero-bias conductance peak in detached flakes of superconducting 2H-TaS$_2$ probed by scanning tunneling spectroscopy
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Galvis, J. A., Chirolli, L., Guillamon, I., Vieira, S., Navarro-Moratalla, E., Coronado, E., Suderow, H., and Guinea, F.
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Condensed Matter - Superconductivity - Abstract
We report an anomalous tunneling conductance with a zero bias peak in flakes of superconducting 2H-TaS$_2$ detached through mechanical exfoliation. To explain the observed phenomenon, we construct a minimal model for a single unit cell layer of superconducting 2H-TaS$_2$ with a simplified 2D Fermi surface and sign-changing Cooper pair wavefunction induced by Coulomb repulsion. Superconductivity is induced in the central $\Gamma$ pocket, where it becomes nodal. We show that weak scattering at the nodal Fermi surface, produced by non-perturbative coupling between tip and sample, gives Andreev states that lead to a zero bias peak in the tunneling conductance. We suggest that reducing dimensionality down to a few atom thick crystals could drive a crossover from conventional to sign changing pairing in the superconductor 2H-TaS$_2$., Comment: 8 pages, 4 figures
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- 2014
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12. Imaging superconducting vortex core and lattice with the scanning tunneling microscope
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Suderow, H., Guillamon, I., Rodrigo, J. G., and Vieira, S.
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Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
The observation of vortices in superconductors was a major breakthrough in developing the conceptual background for superconducting applications. Each vortex carries a flux quantum, and the magnetic field radially decreases from the center. Techniques used to make magnetic field maps, such as magnetic decoration, give vortex lattice images in a variety of systems. However, strong type II superconductors allow penetration of the magnetic field over large distances, of order of the magnetic penetration depth \lambda. Superconductivity survives up to magnetic fields where, for imaging purposes, there is nearly no magnetic contrast. Static and dynamic properties of vortices are largely unknown at such high magnetic fields. Reciprocal space studies using neutron scattering give insight into the collective behavior. But the microscopic details of vortex arrangements and their motion remain difficult to obtain. Direct real space visualization can be made using scanning tunneling microscopy and spectroscopy (STM/S). Instead of using magnetic contrast, the electronic density of states describes spatial variations of the quasiparticle and pair wavefunction properties. These are of order of the superconducting coherence length \xi, which is much smaller than \lambda. In principle, individual vortices can be imaged using STM up to the upper critical field where vortex cores, of size \xi, overlap. In this review, we describe recent advances in vortex imaging made with scanning tunneling microscopy and spectroscopy. We introduce the technique and discuss vortex images which reveal the influence of the Fermi surface distribution of the superconducting gap on the internal structure of vortices, the collective behavior of the lattice in different materials and conditions, and the observation of vortex lattice melting., Comment: Topical review, to appear in Superconductor Science and Technology
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- 2014
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13. Disorder driven inhomogeneous phase in the 2D-superconducting film of titanium nitride
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Kulkarni, P., Vieira, S., Rodrigo, J., Baklanov, M. R., Baturina, T., and Vinokur, V.
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Condensed Matter - Superconductivity - Abstract
Typically the superconducting phase weakens at several points with the increase in disorder before it is distroyed in the 2d-thin films. This may lead to an inhomogeneous superconducting state without a continuous phase. Here we present scanning tunneling spectroscopy measurements at 0.1 K in the disordered polycrystalline film of TiN describing the nanoscale size features of the superconducting state. The imaging shows imcommensurate charge density modulations, originating at the crystalline bounadries, and intercepted on large scale by the beat patterns in the regions of overlap. Electronic coherence is maintained over length scale minimum of crystalline sizes, and suffers scattering across low angle crystalline boundaries. The superconducting state fluctuates at the positions of the charge density modulations and zones of the weak phase appear in the vicinity of the beats. Our data shows that the BCS-like behavior evolves into the V-shaped density of states in such inhomogeneous regions as a result of the competition between the superconducting correlations with that of the strong electron-electron repulsive interactions assisted by the inelastic scattering at the crystalline boundaries., Comment: 38 pages, 8 figures
- Published
- 2014
14. Conductance behavior with temperature and magnetic field in the disordered films of titanium nitride
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Kulkarni, P., Suderow, H., Rodrigo, J., Vieira, S., Baklanov, M. R., Baturina, T., and Vinokur, V.
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Condensed Matter - Superconductivity - Abstract
We report in this paper the temperature and mangetic field dependence of the conductance in the polycrystalline film of titanium nitride, before and after heating at ambient conditions. The difference between the two films is the room temperature sheet resistance which remains within 15 percent and both the films show superconducting transition at lower temperatures. The zero field and the high field data, respectively, corresponds to the superconducting and the normal states. Both the films display Atshuler-Aronov zero bias anamoly in their normal states, and the superconducting gap openeing up at low fields. However the heated film has a smaller gap owing to more pronounced zero bias suppression of the density of states. The normal states in both the films are similar to the quasi-2d-disordered metal and its behavior is studied with temperature. Our data suggests that the zero bias anamoly suppresses the superconducting gap with increase in the disorder., Comment: 5 pages, 7 figures
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- 2014
15. Local electronic properties in the superconducting and the normal phase in the disordered film of titanium nitride
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Kulkarni, P., Suderow, H., Vieira, S., Baklanov, M. R., Baturina, T., and Vinokur, V.
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Condensed Matter - Superconductivity - Abstract
We present in this paper the conductance maps at 100 mK in the disordered polycrystalline film of titanium nitride (TiN). At 5 nm, the film is close to quasi-two dimensional limit and exhibits features pertaining to the superconductor to insulator transition. We measured conductance maps at zero field and at 4 T, which represent the superconducting and the normal phase, respectively. The conductance map at 4 T is uniform, in which the conductance behavior, with logarithmic variation, resembles to the disorder enhanced electron-electron interaction in the two dimensional metallic phase. At low fields we observe the spatial variations of the conductance in the superconducting phase. At several places the superconducting energy gap fluctuates to an extent that the quasi-particle peaks are absent in the conductance curves. The conductance map over a region encompassing only few crystallites suggests that the inhomogeneities in the superconducting phase related to the spatial variations of the electronic density are across the crystalline boundaries., Comment: 5 pages, 7 figures
- Published
- 2014
16. Publisher Correction: Artisanal shark fishing in Milne Bay Province, Papua New Guinea: biomass estimation from genetically identified shark and ray fins
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Appleyard, S. A., White, W. T., Vieira, S., and Sabub, B.
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- 2021
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17. Superconductivity and magnetism on flux grown single crystals of NiBi3
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Silva, B., Luccas, R. F., Nemes, N. M., Hanko, J., Kulkarni, M. R. Osorio P., Mompean, F., Garcia-Hernandez, M., Ramos, M. A., Vieira, S., and Suderow, H.
- Subjects
Condensed Matter - Superconductivity - Abstract
We present resistivity, magnetization and specific heat measurements on flux grown single crystals of NiBi3. We find typical behavior of a type-II superconductor, with, however, a sizable magnetic signal in the superconducting phase. There is a hysteretic magnetization characteristic of a ferromagnetic compound. By following the magnetization as a function of temperature, we find a drop at temperatures corresponding to the Curie temperature of ferromagnetic amorphous Ni. Thus, we assign the magnetism in NiBi$_3$ crystals to amorphous Ni impurities.
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- 2013
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18. Low temperature magnetic transitions of single crystal HoBi
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Fente, A., Suderow, H., Vieira, S., Nemes, N. M., García-Hernández, M., Bud'ko, S. L., and Canfield, P. C.
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Condensed Matter - Materials Science - Abstract
We present resistivity, specific heat and magnetization measurements in high quality single crystals of HoBi, with a residual resistivity ratio of 126. We find, from the temperature and field dependence of the magnetization, an antiferromagnetic transition at 5.7 K, which evolves, under magnetic fields, into a series of up to five metamagnetic phases., Comment: 5 pages, 5 figures
- Published
- 2013
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19. Supercurrent on a vortex core in 2H-NbSe$_2$: current driven scanning tunneling spectroscopy
- Author
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Maldonado, A., Vieira, S., and Suderow, H.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
We report current driven scanning tunneling spectroscopy (CDSTS) measurements at very low temperatures on vortices in 2H-NbSe2. We find that a current produces an increase of the density of states at the Fermi level in between vortices, and a reduction of the zero bias peak at the vortex center. This occurs well below the de-pairing current. We conclude that a supercurrent affects the low energy part of the superconducting gap structure of 2H-NbSe2., Comment: 5 pages, 5 figures
- Published
- 2013
- Full Text
- View/download PDF
20. Scanning Tunneling Microscopy in the superconductor LaSb2
- Author
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Galvis, J. A., Suderow, H., Vieira, S., Bud'ko, S. L., and Canfield, P. C.
- Subjects
Condensed Matter - Superconductivity - Abstract
We present very low temperature (0.15 K) scanning tunneling microscopy and spectroscopy experiments in the layered superconductor LaSb$_2$. We obtain topographic microscopy images with surfaces showing hexagonal and square atomic size patterns, and observe in the tunneling conductance a superconducting gap. We find well defined quasiparticle peaks located at a bias voltage comparable to the weak coupling s-wave BCS expected gap value (0.17 meV). The amount of states at the Fermi level is however large and the curves are significantly broadened. We find T$_c$ of 1.2 K by following the tunneling conductance with temperature., Comment: 5 pages, 4 figures
- Published
- 2013
- Full Text
- View/download PDF
21. Overview of semi-sinusoidal stellar variability with the CoRoT satellite
- Author
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De Medeiros, J. R., Lopes, C. E. Ferreira, Leao, I. C., Martins, B. L. Canto, Catelan, M., Baglin, A., Vieira, S., Bravo, J. P., Cortes, C., de Freitas, D. B., Janot-Pacheco, E., Maciel, S. C., Melo, C. H. F., Osorio, Y., de Mello, G. F. Porto, and Valio, A.
- Subjects
Astrophysics - Solar and Stellar Astrophysics - Abstract
To date, the CoRoT space mission has produced more than 124,471 light curves. Classifying these curves in terms of unambiguous variability behavior is mandatory for obtaining an unbiased statistical view on their controlling root-causes. The present study provides an overview of semi-sinusoidal light curves observed by the CoRoT exo-field CCDs. We selected a sample of 4,206 light curves presenting well-defined semi-sinusoidal signatures. The variability periods were computed based on Lomb-Scargle periodograms, harmonic fits, and visual inspection. Color-period diagrams for the present sample show the trend of an increase of the variability periods as long as the stars evolve. This evolutionary behavior is also noticed when comparing the period distribution in the Galactic center and anti-center directions. These aspects indicate a compatibility with stellar rotation, although more information is needed to confirm their root-causes. Considering this possibility, we identified a subset of three Sun-like candidates by their photometric period. Finally, the variability period versus color diagram behavior was found to be highly dependent on the reddening correction., Comment: 12 pages, 16 figures, A&A accepted
- Published
- 2013
- Full Text
- View/download PDF
22. Pressure dependence of superconducting critical temperature and upper critical field of 2H-NbS2
- Author
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Tissen, V. G., Osorio, M. R., Brison, J. P., Nemes, N. M., Garcia-Hernandez, M., Cario, L., Rodiere, P., Vieira, S., and Suderow, H.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
We present measurements of the superconducting critical temperature Tc and upper critical field Hc2 as a function of pressure in the transition metal dichalcogenide 2H-NbS2 up to 20 GPa. We observe that Tc increases smoothly from 6K at ambient pressure to about 8.9K at 20GPa. This range of increase is comparable to the one found previously in 2H-NbSe2. The temperature dependence of the upper critical field Hc2(T) of 2H-NbS2 varies considerably when increasing the pressure. At low pressures, Hc2(0) decreases, and at higher pressures both Tc and Hc2(0) increase simultaneously. This points out that there are pressure induced changes of the Fermi surface, which we analyze in terms of a simplified two band approach., Comment: 5 pages, 5 figures
- Published
- 2013
- Full Text
- View/download PDF
23. Majorana Fermions in Topological Superconducting Metallic Nanowires probed by a Superconducting Condensate
- Author
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Rodrigo, J. G., Crespo, V., Suderow, H., Vieira, S., and Guinea, F.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
We report on several low temperature experiments supporting the presence of Majorana fermions in superconducting lead nanowires fabricated with a scanning tunneling microscope. These nanowires are the connecting bridges between the STM tip and the sample resulting from indentation processes. We show here that by a controlled tuning of the geometry of the nanowire region, in which superconductivity is confined by applied magnetic fields, the conductance curves obtained in these situations are indicative of topological superconductivity and Majorana fermions. The most prominent feature of this behavior is the emergence of a zero bias peak in the conductance curves, superimposed on a background characteristic of the conductance between a normal metal and a superconductor in the Andreev regime. The zero bias peak emerges in some nanowires when a magnetic field larger that the lead bulk critical field is applied. This field drives one of the electrodes into the normal state while the other, the tip, remains superconducting on its apex. Meanwhile a topological superconducting state appears in the connecting nanowire of nanometric size., Comment: Contribution to a New Journal of Physics topical issue
- Published
- 2013
24. Temperature dependent tunneling spectroscopy in the heavy fermion CeRu2Si2 and in the antiferromagnet CeRh2Si2
- Author
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Maldonado, A., Suderow, H., Vieira, S., Aoki, D., and Flouquet, J.
- Subjects
Condensed Matter - Strongly Correlated Electrons - Abstract
CeRu2Si2 and CeRh2Si2 are two similar heavy fermion stoichiometric compounds located on the two sides of the magnetic quantum critical phase transition. CeRh2Si2 is an antiferromagnet below T_N=36 K with moderate electronic masses whereas CeRu2Si2 is a paramagnetic metal with particularly heavy electrons. Here we present tunneling spectroscopy measurements as a function of temperature (from 0.15 K to 45 K). The tunneling conductance at 0.15 K reveals V-shaped dips around the Fermi level in both compounds, which disappear in CeRu2Si2 above the coherence temperature, and above the N\'eel temperature in CeRh2Si2. In the latter case, two different kinds of V-shaped tunneling conductance dips are found.
- Published
- 2012
- Full Text
- View/download PDF
25. Magnetic and superconducting phase diagrams in ErNi2B2C
- Author
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Galvis, J. A., Crespo, M., Guillamón, I., Suderow, H., Vieira, S., Hernández, M. García, Bud'ko, S., and Canfield, P. C.
- Subjects
Condensed Matter - Superconductivity - Abstract
We present measurements of the superconducting upper critical field Hc2(T) and the magnetic phase diagram of the superconductor ErNi2B2C made with a scanning tunneling microscope (STM). The magnetic field was applied in the basal plane of the tetragonal crystal structure. We have found large gapless regions in the superconducting phase diagram of ErNi2B2C, extending between different magnetic transitions. A close correlation between magnetic transitions and Hc2(T) is found, showing that superconductivity is strongly linked to magnetism., Comment: 5 pages, 4 figures
- Published
- 2012
- Full Text
- View/download PDF
26. Scanning tunneling spectroscopy of layers of superconducting 2H-TaSe$_\textbf{2}$: Evidence for a zero bias anomaly in single layers
- Author
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Galvis, J. A., Rodière, P., Guillamón, I., Osorio, M. R., Rodrigo, J. G., Cario, L., Navarro-Moratalla, E., Coronado, E., Vieira, S., and Suderow, H.
- Subjects
Condensed Matter - Superconductivity - Abstract
We report a characterization of surfaces of the dichalcogenide TaSe$_2$ using scanning tunneling microscopy and spectroscopy (STM/S) at 150 mK. When the top layer has the 2H structure and the layer immediately below the 1T structure, we find a singular spatial dependence of the tunneling conductance below 1 K, changing from a zero bias peak on top of Se atoms to a gap in between Se atoms. The zero bias peak is additionally modulated by the commensurate $3a_0 \times 3a_0$ charge density wave of 2H-TaSe$_2$. Multilayers of 2H-TaSe$_2$ show a spatially homogeneous superconducting gap with a critical temperature also of 1 K. We discuss possible origins for the peculiar tunneling conductance in single layers., Comment: 10 pages, 10 figures
- Published
- 2012
- Full Text
- View/download PDF
27. Demonstration experiments for solid state physics using a table top mechanical Stirling refrigerator
- Author
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Osorio, M. R., Morales, A. Palacio, Rodrigo, J. G., Suderow, H., and Vieira, S.
- Subjects
Physics - Physics Education ,Condensed Matter - Superconductivity - Abstract
Liquid free cryogenic devices are acquiring importance in basic science and engineering. But they can also lead to improvements in teaching low temperature an solid state physics to graduate students and specialists. Most of the devices are relatively expensive, but small sized equipment is slowly becoming available. Here, we have designed several simple experiments which can be performed using a small Stirling refrigerator. We discuss the measurement of the critical current and temperature of a bulk YBa2Cu3O(7-d) (YBCO) sample, the observation of the levitation of a magnet over a YBCO disk when cooled below the critical temperature and the observation of a phase transition using ac calorimetry. The equipment can be easily handled by students, and also used to teach the principles of liquid free cooling.
- Published
- 2012
- Full Text
- View/download PDF
28. Topological superconductivity in lead nanowires
- Author
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Rodrigo, J. G., Crespo, V., Suderow, H., Vieira, S., and Guinea, F.
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
Superconductors with an odd number of bands crossing the Fermi energy have topologically protected Andreev states at interfaces, including Majorana states in one dimensional geometries. Superconductivity, a low number of 1D channels, large spin orbit coupling, and a sizeable Zeeman energy, are present in lead nanowires produced by nanoindentation of a Pb tip on a Pb substrate, in magnetic fields higher than the Pb bulk critical field. A number of such devices have been analyzed. In some of them, the dependence of the critical current on magnetic field, and the Multiple Andreev Reflections observed at finite voltages, are compatible with the existence of topological superconductivity.
- Published
- 2012
- Full Text
- View/download PDF
29. Scanning microscopies of superconductors at very low temperatures
- Author
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Crespo, V., Maldonado, A., Galvis, J. A., Kulkarni, P., Guillamon, I., Rodrigo, J. G., Suderow, H., Vieira, S., Banerjee, S., and Rodiere, P.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
We discuss basics of scanning tunneling microscopy and spectroscopy (STM/S) of the superconducting state with normal and superconducting tips. We present a new method to measure the local variations in the Andreev reflection amplitude between a superconducting tip and the sample. This method is termed Scanning Andreev Reflection Spectroscopy (SAS). We also briefly discuss vortex imaging with STM/S under an applied current through the sample, and show the vortex lattice as a function of the angle between the magnetic field and sample's surface.
- Published
- 2012
- Full Text
- View/download PDF
30. Tunneling spectroscopy of the superconducting state of URu2Si2
- Author
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Maldonado, A., Guillamon, I., Rodrigo, J. G., Suderow, H., Vieira, S., Aoki, D., and Flouquet, J.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
We present measurements of the superconducting gap of URu$_2$Si$_2$ made with scanning tunneling microscopy (STM) using a superconducting tip of Al. We find tunneling conductance curves with a finite value at the Fermi level. The density of states is V shaped at low energies, and the quasiparticle peaks are located at values close to the expected superconducting gap from weak coupling BCS theory. Our results point to rather opened gap structures and gap nodes on the Fermi surface.
- Published
- 2012
- Full Text
- View/download PDF
31. Chiral charge order in the superconductor 2H-TaS2
- Author
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Guillamon, I., Suderow, H., Rodrigo, J. G., Vieira, S., Rodiere, P., Cario, L., Navarro-Moratalla, E., Marti-Gastaldo, C., and Coronado, E.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
We find chiral charge order in the superconductor 2H-TaS2 using Scanning Tunneling Microscopy and Spectroscopy (STM/S) at 0.1 K. Topographic images show hexagonal atomic lattice and charge density wave (CDW) with clockwise and counterclockwise charge modulations. Tunneling spectroscopy reveals the superconducting density of states, disappearing at Tc = 1.75 K and showing a wide distribution of values of the superconducting gap, centered around \Delta=0.28 meV.
- Published
- 2011
- Full Text
- View/download PDF
32. Direct observation of stress accumulation and relaxation in small bundles of superconducting vortices in tungsten thin-films
- Author
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Guillamon, I., Suderow, H., Vieira, S., Sese, J., Cordoba, R., De Teresa, J. M., and Ibarra, M. R.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Soft Condensed Matter - Abstract
We study the behavior of bundles of superconducting vortices when increasing the magnetic field using scanning tunneling microscopy and spectroscopy (STM/S) at 100 mK. Pinning centers are given by features on the surface corrugation. We find strong net vortex motion in a bundle towards a well defined direction. We observe continuos changes of the vortex arrangements, and identify small displacements, which stress and deform the vortex bundle, separated by larger re-arrangements or avalanches, which release accumulated stress., Comment: 4 pages, 4 figures, and 2 EPAPS figures
- Published
- 2011
- Full Text
- View/download PDF
33. Direct observation of melting in a 2-D superconducting vortex lattice
- Author
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Guillamon, I., Suderow, H., Fernandez-Pacheco, A., Sese, J., Cordoba, R., De Teresa, J. M., Ibarra, M. R., and Vieira, S.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Soft Condensed Matter - Abstract
Topological defects such as dislocations and disclinations are predicted to determine the twodimensional (2-D) melting transition. In 2-D superconducting vortex lattices, macroscopic measurements evidence melting close to the transition to the normal state. However, the direct observation at the scale of individual vortices of the melting sequence has never been performed. Here we provide step by step imaging through scanning tunneling spectroscopy of a 2-D system of vortices up to the melting transition in a focused-ion-beam nanodeposited W-based superconducting thin film. We show directly the transition into an isotropic liquid below the superconducting critical temperature. Before that, we find a hexatic phase, characterized by the appearance of free dislocations, and a smectic-like phase, possibly originated through partial disclination unbinding. These results represent a significant step in the understanding of melting of 2-D systems, with impact across several research fields, such as liquid crystal molecules, or lipids in membranes., Comment: Submitted to Nature Physics
- Published
- 2009
- Full Text
- View/download PDF
34. Superconducting density of states at the border of an amorphous thin film grown by focused-ion-beam
- Author
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Guillamon, I., Suderow, H., Vieira, S., Fernandez-Pacheco, A., Sese, J., Cordoba, R., De Teresa, J. M., and Ibarra, M. R.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
We present very low temperature Scanning Tunneling Microscopy and Spectroscopy (STM/S) measurements of a W based amorphous thin film grown with focused-ion-beam. In particular, we address the superconducting properties close to the border, where the thickness of the superconducting film decreases, and the Au substrate emerges. When approaching the Au substrate, the superconducting tunneling conductance strongly increases around the Fermi level, and the quasiparticle peaks do not significantly change its position. Under magnetic fields, the vortex lattice is observed, with vortices positioned very close to the Au substrate., Comment: To appear in Journal of Physics: Conference series
- Published
- 2009
- Full Text
- View/download PDF
35. Evolution of the local superconducting density of states in ErRh$_4$B$_{4}$ close to the ferromagnetic transition
- Author
-
Crespo, V., Rodrigo, J. G., Suderow, H., Vieira, S., Hinks, D., and Schuller, I. K.
- Subjects
Condensed Matter - Superconductivity - Abstract
We present local tunneling spectroscopy experiments in the superconducting and ferromagnetic phases of the reentrant superconductor ErRh$_4$B$_{4}$. The tunneling conductance curves jump from showing normal to superconducting features within a few mK close to the ferromagnetic transition temperature, with a clear hysteretic behavior. Within the ferromagnetic phase, we do not detect any superconducting correlations. Within the superconducting phase we find a peculiar V-shaped density of states at low energies, which is produced by the magnetically modulated phase that coexists with superconductivity just before ferromagnetism sets in., Comment: 5 pages, 4 figures
- Published
- 2009
- Full Text
- View/download PDF
36. Neuronal deletion of GSK3β increases microtubule speed in the growth cone and enhances axon regeneration via CRMP-2 and independently of MAP1B and CLASP2
- Author
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Wittmann, Torsten, Liz, MA, Mar, FM, Santos, TE, Pimentel, HI, Marques, AM, Morgado, MM, Vieira, S, Sousa, VF, and Pemble, H
- Abstract
© Liz et al.Background: In the adult central nervous system, axonal regeneration is abortive. Regulators of microtubule dynamics have emerged as attractive targets to promote axonal growth following injury as microtubule organization is pivotal for growth
- Published
- 2014
37. Iron requirements of broiler chickens as affected by supplemental phytase
- Author
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Feijo, J C, primary, Vieira, S L, additional, Horn, R M, additional, Altevogt, W E, additional, and Tormes, G, additional
- Published
- 2023
- Full Text
- View/download PDF
38. Nodeless spin triplet superconducting gap in Sr2RuO4
- Author
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Suderow, H., Crespo, V., Guillamon, I., Vieira, S., Servant, F., Lejay, P., Brison, J. P., and Flouquet, J.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
We report on tunneling spectroscopy measurements using a Scanning Tunneling Microscope (STM) on the spin triplet superconductor Sr2RuO4. We find a negligible density of states close to the Fermi level and a fully opened gap with a value of $\Delta$=0.28 meV, which disappears at T$_c$ = 1.5 K. $\Delta$ is close to the result expected from weak coupling BCS theory ($\Delta_0$=1.76kBT$_c$ = 0.229 meV). Odd parity superconductivity is associated with a fully isotropic gap without nodes over a significant part of the Fermi surface.
- Published
- 2008
- Full Text
- View/download PDF
39. Superconducting density of states and vortex cores of 2H-NbS2
- Author
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Guillamon, I., Suderow, H., Vieira, S., Cario, L., Diener, P., and Rodiere, P.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
Scanning tunneling microscopy and spectroscopy (STM/S) measurements in the superconducting dichalcogenide 2H-NbS2 show a peculiar superconducting density of states with two well defined features at 0.97 meV and 0.53 meV, located respectively above and below the value for the superconducting gap expected from single band s-wave BCS model (D=1.76kBTc=0.9 meV). Both features have a continuous temperature evolution and disappear at Tc = 5.7 K. Moreover, we observe the hexagonal vortex lattice with radially symmetric vortices and a well developed localized state at the vortex cores. The sixfold star shape characteristic of the vortex lattice of the compound 2H-NbSe2 is, together with the charge density wave order (CDW), absent in 2H-NbS2., Comment: 5 pages, 4 figures
- Published
- 2008
- Full Text
- View/download PDF
40. Nanoscale superconducting properties of amorphous W-based deposits grown with focused-ion-beam
- Author
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Guillamon, I., Suderow, H., Vieira, S., Fernandez-Pacheco, A., Sese, J., Cordoba, R., De Teresa, J. M., and Ibarra, M. R.
- Subjects
Condensed Matter - Superconductivity - Abstract
We present very low temperature Scanning Tunneling Microscopy and Spectroscopy (STM/S) measurements in W-based amorphous superconducting nanodeposits grown using a metal-organic precursor and focused-ion-beam. The superconducting gap closely follows s-wave BCS theory, and STS images under magnetic fields show a hexagonal vortex lattice whose orientation is related to features observed in the topography through STM. Our results demonstrate that the superconducting properties at the surface of these deposits are very homogeneous, down to atomic scale. This, combined with the huge nanofabrication possibilities of the focused-ion-beam technique, paves the way to use focused-ion-beam to make superconducting circuitry of many different geometries.
- Published
- 2008
- Full Text
- View/download PDF
41. Gap opening with ordering in PrFe4P12 studied by local tunneling spectroscopy
- Author
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Suderow, H., Behnia, K., Guillamon, I., Crespo, V., Vieira, S., Kikuchi, D., Aoki, Y., Sugawara, H., and Sato, H.
- Subjects
Condensed Matter - Strongly Correlated Electrons - Abstract
We present measurements of the local tunneling density of states in the low temperature ordered state of PrFe4P12. The temperature dependencies of the Fermi level density of states and of the integrated density of states at low bias voltages show anomalies at T=6.5 K, the onset of multipolar ordering as detected by specific heat and other macroscopic measurements. In the ordered phase, we find a local density of states with a V-shape form, indicating a partial gap opening over the Fermi surface. The size of the gap according to the tunneling spectra is about 2 meV., Comment: 4 pages, 3 figures
- Published
- 2008
- Full Text
- View/download PDF
42. Intrinsic atomic scale modulations of the superconducting gap of 2H-NbSe2
- Author
-
Guillamon, I., Suderow, H., Guinea, F., and Vieira, S.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
We present scanning tunneling microscopy and spectroscopy measurements at 100mK in the superconducting material 2H-NbSe2 that show well defined features in the superconducting density of states changing in a pattern closely following atomic periodicity. Our experiment demonstrates that the intrinsic superconducting density of states can show atomic size modulations, which reflect the reciprocal space structure of the superconducting gap. In particular we obtain that the superconducting gap of 2H-NbSe2 has six fold modulated components at 0.75 mV and 1.2 mV.Moreover, we also find related atomic size modulations inside vortices, demonstrating that the much discussed star shape vortex structure produced by localized states inside the vortex cores, has a, hitherto undetected, superposed atomic size modulation. The tip substrate interaction in an anisotropic superconductor has been calculated, giving position dependent changes related to the observed gap anisotropy., Comment: 9 pages, 5 figures. Discussion extended, references added, one more figure
- Published
- 2007
- Full Text
- View/download PDF
43. Scanning tunneling spectroscopy with superconducting tips of Al
- Author
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Guillamon, I., Suderow, H., Vieira, S., and Rodiere, P.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
We present Scanning Tunneling Spectroscopy measurements at 0.1 K using tips made of Al. At zero field, the atomic lattice and charge density wave of 2HNbSe2 are observed, and under magnetic fields the peculiar electronic surface properties of vortices are precisely resolved. The tip density of states is influenced by the local magnetic field of the vortex, providing for a new probe of the magnetic field at nanometric sizes.
- Published
- 2007
- Full Text
- View/download PDF
44. Scanning tunnelling spectroscopy of the vortex state in NbSe2 using a superconducting tip
- Author
-
Rodrigo, J. G., Crespo, V., and Vieira, S.
- Subjects
Condensed Matter - Superconductivity - Abstract
The vortex electronic structure in the multiband superconductor NbSe2 is studied by means of Scanning Tunneling Spectroscopy (STS) using a superconducting tip. The use of a superconducting tip (Pb) as a probe provides an enhancement of the different features related to the DOS of NbSe2 in the tunneling conductance curves. This use allows the observation of rich patterns of electronic states in the conductance images around the vortex cores in a wide range of temperature, as well as the simultaneous acquisition of Josephson current images in the vortex state., Comment: 5 pages, 5 figures, submitted to Physica C
- Published
- 2007
- Full Text
- View/download PDF
45. Local superconducting density of states of ErNi2B2C
- Author
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Crespo, M., Suderow, H., Vieira, S., Bud'ko, S., and Canfield, P. C.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
We present local tunnelling microscopy and spectroscopy measurements at low temperatures in single crystalline samples of the magnetic superconductor ErNi2B2C. The electronic local density of states shows a striking departure from s-wave BCS theory with a finite value at the Fermi level, which amounts to half of the normal phase density of states., Comment: 9 pages, 3 figures
- Published
- 2005
- Full Text
- View/download PDF
46. Pressure induced effects on the Fermi surface of superconducting 2H-NbSe$_2$
- Author
-
Suderow, H., Tissen, V. G., Brison, J. P., Martinez, J. L., and Vieira, S.
- Subjects
Condensed Matter - Superconductivity - Abstract
The pressure dependence of the critical temperature $T_c$ and upper critical field $H_{c2}(T)$ has been measured up to 19 GPa in the layered superconducting material 2H-NbSe$_2$. Relating the behavior of $H_{c2}(T)$ to Fermi surface parameters, we find that the electron phonon coupling of the 2D Nb 4d derived bands shows a peak at 5 GPa when the charge density wave (CDW) order is suppressed. On the other hand, $T_c(P)$ shows a bell shaped curve with a maximum at 10.5 GPa, well above the pressure for the suppression of the CDW order. Changes in the band structure produce this shift in the maximum of $T_c(P)$, demonstrating that 2H-NbSe$_2$ shows important differences with respect to other compounds where $T_c$ has a maximum in the temperature-density phase diagram shaped by the suppression of another, non-superconducting, ground state., Comment: 5 pages, 4 figures. Small changes in discussion. Typos corrected
- Published
- 2005
- Full Text
- View/download PDF
47. Pressure dependence of the upper critical field of MgB2 and of YNi2B2C
- Author
-
Suderow, H., Tissen, V. G., Brison, J. P., Martinez, J. L., Vieira, S., Lejay, P., Lee, S., and Tajima, S.
- Subjects
Condensed Matter - Superconductivity - Abstract
We present measurements of H$_{c2}(T)$ under pressure in MgB$_2$ and in YNi$_2$B$_2$C. The changes in the shape of H$_{c2}(T)$ are interpreted within current models and show the evolution of the main Fermi surface velocities $v_F$ and electron-phonon coupling parameters $\lambda$ with pressure. In MgB$_2$ the electron-phonon coupling strength of the nearly two dimensional $\sigma$ band, responsible for the high critical temperature, is more affected by pressure than the $\pi$ band coupling, and the hole doping of the $\sigma$ band decreases. In YNi$_2$B$_2$C, the peculiar positive curvature of H$_{c2}(T)$ is weakened by pressure., Comment: 5 pages, 5 figures
- Published
- 2004
- Full Text
- View/download PDF
48. Superconducting nanostructures fabricated with the STM
- Author
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Rodrigo, J. G., Suderow, H., Vieira, S., Bascones, E., and Guinea, F.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
The properties of nanoscopic superconducting structures fabricated with a scanning tunnelling microscope are reviewed, with emphasis on the effects of high magnetic fields. These systems include the smallest superconducting junctions which can be fabricated, and they are a unique laboratory where to study superconductivity under extreme conditions. The review covers a variety of recent experimental results on these systems, highlighting their unusual transport properties, and theoretical models developed for their understanding., Comment: Topical Review, 35 pages, 18 figures (with reduced quality to decrease file size)
- Published
- 2004
49. On the use of STM superconducting tips at very low temperatures
- Author
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Rodrigo, J. G., Suderow, H., and Vieira, S.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
We report on high quality local tunnel spectroscopy measurements in superconductors using in-situ fabricated superconducting tips as counterelectrode. The experiments were made at very low temperatures using a dilution refrigerator and a 3He cryostat. Spectra obtained with superconducting tip and sample of Al show that the spectroscopic resolution of our set-up is of 15 microeV . Following the observation of Josephson current in tunneling regime (with tips of Pb and of Al), we discuss the feasibility of Scanning Josephson Spectroscopy with atomic size resolution. Experiments showing new applications of these superconducting tips under applied external magnetic fields are also reported., Comment: PDF file, 8 pages, accepted for publication in The European Physical Journal B, for the topical issue on Colective phenomena in Mesoscopic systems
- Published
- 2004
- Full Text
- View/download PDF
50. STM study of multiband superconductivity in NbSe2 using a superconducting tip
- Author
-
Rodrigo, J. G. and Vieira, S.
- Subjects
Condensed Matter - Superconductivity - Abstract
We present a method to produce superconducting tips to be used in Scanning Tunneling Microscopy/Spectroscopy experiments. We use these tips to investigate the evolution of the electronic density of states of NbSe2 from 0.3K up to its critical temperature (7.2K). The use of a superconducting tip (Pb) as ounterelectrode provides an enhancement of the different features related to the DOS of NbSe2 in the tunneling conductance curves, along all the studied thermal range. The analysis of the experimental results gives evidence of the presence of multiband superconductivity in NbSe2., Comment: 5 pages, 5 figures, PDF file
- Published
- 2004
- Full Text
- View/download PDF
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