26 results on '"Vieira S"'
Search Results
2. 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., Rodière, Pierre, Osorio, M.R., Navarro-Moratalla, E, Nemes, N.M., Tissen, V.G., Cario, L, Coronado, E, García-Hernández, M, Vieira, S, Núñez-Regueiro, M, Suderow, H, Magnétisme et Supraconductivité (MagSup ), Institut Néel (NEEL), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Departamento de Fisica de la Materia Condensada [Madrid] (FMC), Facultad de Ciencas [Madrid], Universidad Autonoma de Madrid (UAM)-Universidad Autonoma de Madrid (UAM), Instituto de Ciencia Molecular (ICMol), Universitat de València (UV), Dept Fis Applicada, Universidad Complutense de Madrid = Complutense University of Madrid [Madrid] (UCM), Institut des Matériaux Jean Rouxel (IMN), Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Ecole Polytechnique de l'Université de Nantes (EPUN), Université de Nantes (UN)-Université de Nantes (UN), Instituto de Investigaciones de la Amazonía Peruana (IIAP), Instituto de Ciencia de Materiales de Madrid (ICMM), Consejo Superior de Investigaciones Científicas [Madrid] (CSIC), and Universidade Estadual de Campinas (UNICAMP)
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7470Xa ,[PHYS.COND.CM-S]Physics [physics]/Condensed Matter [cond-mat]/Superconductivity [cond-mat.supr-con] ,Superconductivity (cond-mat.supr-con) ,Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed Matter - Superconductivity ,FOS: Physical sciences ,7445Lr ,7425Dw ,[PHYS.COND.CM-SCE]Physics [physics]/Condensed Matter [cond-mat]/Strongly Correlated Electrons [cond-mat.str-el] - 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
- Full Text
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3. Magnetic field dependence of the density of states in the multiband superconductor $��$-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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Superconductivity (cond-mat.supr-con) ,Condensed Matter::Superconductivity ,FOS: Physical sciences - Abstract
We present very low temperature scanning tunneling microscopy (STM) experiments on single crystalline samples of the superconductor $��$-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 $��$-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., 8 pages, 7 figures
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- 2015
- Full Text
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4. Zero-bias conductance peak in detached flakes of superconducting 2H-TaS$_2$ probed by scanning tunneling spectroscopy
- Author
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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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Superconductivity (cond-mat.supr-con) ,Condensed Matter::Superconductivity ,Condensed Matter - Superconductivity ,FOS: Physical sciences - 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
- Published
- 2014
5. 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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Superconductivity (cond-mat.supr-con) ,Condensed Matter::Materials Science ,Condensed Matter::Superconductivity ,Condensed Matter - Superconductivity ,FOS: Physical sciences - 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., 5 pages, 7 figures
- Published
- 2014
6. 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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Superconductivity (cond-mat.supr-con) ,Condensed Matter::Materials Science ,Condensed Matter::Superconductivity ,Condensed Matter - Superconductivity ,FOS: Physical sciences - 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., 5 pages, 7 figures
- Published
- 2014
7. Disorder driven inhomogeneous phase in the 2D-superconducting film of titanium nitride
- Author
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Kulkarni, P., Vieira, S., Rodrigo, J., Baklanov, M. R., Baturina, T., and Vinokur, V.
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Superconductivity (cond-mat.supr-con) ,Condensed Matter - Superconductivity ,Condensed Matter::Superconductivity ,FOS: Physical sciences - 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
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- 2014
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8. Supercurrent on a vortex core in 2H-NbSe$_2$: current driven scanning tunneling spectroscopy
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Maldonado, A., Vieira, S., and Suderow, H.
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Superconductivity (cond-mat.supr-con) ,Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed Matter - Superconductivity ,Condensed Matter::Superconductivity ,FOS: Physical sciences - 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
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9. 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.
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Superconductivity (cond-mat.supr-con) ,Condensed Matter::Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Superconductivity ,Condensed Matter::Superconductivity ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,FOS: Physical sciences - 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
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10. Scanning tunneling spectroscopy of layers of superconducting 2H-TaSe$_\textbf{2}$: Evidence for a zero bias anomaly in single layers
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Galvis, J. A., Rodi��re, P., Guillam��n, I., Osorio, M. R., Rodrigo, J. G., Cario, L., Navarro-Moratalla, E., Coronado, E., Vieira, S., and Suderow, H.
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Superconductivity (cond-mat.supr-con) ,Condensed Matter - Superconductivity ,FOS: Physical sciences - 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., 10 pages, 10 figures
- Published
- 2012
11. Topological superconductivity in lead nanowires
- Author
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Rodrigo, J. G., Crespo, V., Suderow, H., Vieira, S., and Guinea, F.
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Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter::Superconductivity ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,FOS: Physical sciences ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect - 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.
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- 2012
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12. Tunneling spectroscopy of the superconducting state of URu2Si2
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Maldonado, A., Guillamon, I., Rodrigo, J. G., Suderow, H., Vieira, S., Aoki, D., Flouquet, J., and UAM. Departamento de Física de la Materia Condensada
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Superconductivity (cond-mat.supr-con) ,Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed Matter - Superconductivity ,Condensed Matter::Superconductivity ,Física ,FOS: Physical sciences - Abstract
We present measurements of the superconducting gap of URu 2Si 2 made with scanning tunneling microscopy 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, This work was supported by the Spanish MICINN and MEC (Consolider Ingenio Molecular Nanoscience CSD2007-00010 program, FIS2011-23488, ACI-2009-0905, and FPU grant), by the Comunidad de Madrid through program Nanobiomagnet, and by ERC (NewHeavyFermion) and French ANR projects (CORMAT, SINUS, DELICE)
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- 2012
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13. Direct observation of melting in a 2-D superconducting vortex lattice
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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.
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Condensed Matter::Soft Condensed Matter ,Superconductivity (cond-mat.supr-con) ,Condensed Matter - Superconductivity ,Condensed Matter::Superconductivity ,Soft Condensed Matter (cond-mat.soft) ,FOS: Physical sciences ,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
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- 2009
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14. Evolution of the local superconducting density of states in ErRh$_4$B$_{4}$ close to the ferromagnetic transition
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Crespo, V., Rodrigo, J. G., Suderow, H., Vieira, S., Hinks, D., and Schuller, I. K.
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Superconductivity (cond-mat.supr-con) ,Condensed Matter - Superconductivity ,Condensed Matter::Superconductivity ,FOS: Physical sciences ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect - 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
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- 2009
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15. Nodeless spin triplet superconducting gap in Sr2RuO4
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Suderow, H., Crespo, V., Guillamon, I., Vieira, S., Servant, F., Lejay, P., Brison, J. P., and Flouquet, J.
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Superconductivity (cond-mat.supr-con) ,Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed Matter - Superconductivity ,Condensed Matter::Superconductivity ,FOS: Physical sciences - 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
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16. 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 ,Strongly Correlated Electrons (cond-mat.str-el) ,FOS: Physical sciences - 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
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17. Intrinsic atomic scale modulations of the superconducting gap of 2H-NbSe2
- Author
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Guillamon, I., Suderow, H., Guinea, F., and Vieira, S.
- Subjects
Superconductivity (cond-mat.supr-con) ,Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed Matter::Superconductivity ,Condensed Matter - Superconductivity ,FOS: Physical sciences - 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., 9 pages, 5 figures. Discussion extended, references added, one more figure
- Published
- 2007
18. 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.
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Superconductivity (cond-mat.supr-con) ,Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed Matter::Superconductivity ,Condensed Matter - Superconductivity ,FOS: Physical sciences - 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., 9 pages, 3 figures
- Published
- 2005
19. Pressure induced effects on the Fermi surface of superconducting 2H-NbSe$_2$
- Author
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Suderow, H., Tissen, V. G., Brison, J. P., Martinez, J. L., and Vieira, S.
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Superconductivity (cond-mat.supr-con) ,Condensed Matter - Superconductivity ,Condensed Matter::Superconductivity ,FOS: Physical sciences ,Condensed Matter::Strongly Correlated Electrons - 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
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20. Superconducting nanostructures fabricated with the STM
- Author
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Rodrigo, J. G., Suderow, H., Vieira, S., Bascones, E., and Guinea, F.
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Superconductivity (cond-mat.supr-con) ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Superconductivity ,Condensed Matter::Superconductivity ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,FOS: Physical sciences - 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)
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- 2004
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21. Pressure dependence of the upper critical field of MgB2 and of YNi2B2C
- Author
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Suderow, H., Tissen, V. G., Brison, J. P., Martinez, J. L., Vieira, S., Lejay, P., Lee, S., and Tajima, S.
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Superconductivity (cond-mat.supr-con) ,Condensed Matter - Superconductivity ,Condensed Matter::Superconductivity ,FOS: Physical sciences - 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
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22. Very Low Temperature Tunnelling Spectroscopy in the heavy fermion superconductor PrOs$_4$Sb$_{12}$
- Author
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Suderow, H., Vieira, S., Strand, J. D., Bud'ko, S., and Canfield, P. C.
- Subjects
Condensed Matter::Quantum Gases ,Superconductivity (cond-mat.supr-con) ,Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed Matter - Superconductivity ,Condensed Matter::Superconductivity ,FOS: Physical sciences - Abstract
We present scanning tunnelling spectroscopy measurements on the heavy fermion superconductor PrOs$_4$Sb$_{12}$. Our results show that the superconducting gap opens over a large part of the Fermi surface. The deviations from isotropic BCS s-wave behavior are discussed in terms of a finite distribution of values of the superconducting gap., Comment: 4 pages, 4 figures
- Published
- 2003
- Full Text
- View/download PDF
23. Tunneling spectroscopy in the magnetic superconductor TmNi2B2C
- Author
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Suderow, H., Martinez-Samper, P., Vieira, S., Luchier, N., Brison, J. P., and Canfield, P.
- Subjects
Superconductivity (cond-mat.supr-con) ,Condensed Matter - Superconductivity ,Condensed Matter::Superconductivity ,FOS: Physical sciences - Abstract
We present new measurements about the tunneling conductance in the borocarbide superconductor TmNi$_2$B$_2$C. The results show a very good agreement with weak coupling BCS theory, without any lifetime broadening parameter, over the whole sample surface. We detect no particular change of the tunneling spectroscopy below 1.5K, when both the antiferromagnetic (AF) phase and the superconducting order coexist., Comment: Submitted to Phys. Rev. B, Rapid Communications
- Published
- 2001
- Full Text
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24. Onset of dissipation in ballistic atomic wires
- Author
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Agrait, N., Untiedt, C., Rubio-Bollinger, G., and Vieira, S.
- Subjects
Condensed Matter (cond-mat) ,Physics::Atomic and Molecular Clusters ,FOS: Physical sciences ,Condensed Matter ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect - Abstract
Electronic transport at finite voltages in free-standing gold atomic chains of up to 7 atoms in length is studied at low temperatures using a scanning tunneling microscope (STM). The conductance vs voltage curves show that transport in these single-mode ballistic atomic wires is non-dissipative up to a finite voltage threshold of the order of several mV. The onset of dissipation and resistance within the wire corresponds to the excitation of the atomic vibrations by the electrons traversing the wire and is very sensitive to strain., Comment: Revtex4, 4 pages, 3 figs
- Published
- 2001
- Full Text
- View/download PDF
25. Andreev scattering in nanoscopic junctions at high magnetic fields
- Author
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Suderow, H., Bascones, E., Belzig, W., Guinea, F., and Vieira, S.
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter::Superconductivity ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,FOS: Physical sciences ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect - Abstract
We report on the measurement of multiple Andreev resonances at atomic size point contacts between two superconducting nanostructures of Pb under magnetic fields higher than the bulk critical field, where superconductivity is restricted to a mesoscopic region near the contact. The small number of conduction channels in this type of contacts permits a quantitative comparison with theory through the whole field range. We discuss in detail the physical properties of our structure, in which the normal bulk electrodes induce a proximity effect into the mesoscopic superconducting part., Comment: 4 pages
- Published
- 1999
- Full Text
- View/download PDF
26. Point-contact spectroscopy on URu$_2$Si$_2$
- Author
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Rodrigo, J. G., Guinea, F., Vieira, S., and Aliev, F. G.
- Subjects
Condensed Matter (cond-mat) ,FOS: Physical sciences ,Condensed Matter - Abstract
Tunnel and point contact experiments have been made in a URu$_2$Si$_2$ single crystal along the c-axis. The experiments were performed changing temperature and contact size in a low temperature scanning tunneling microscope. A resonance develops at the Fermi level at $T\sim 60$ K. This resonance splits and becomes asymmetric when the 17.5 K phase transition is crossed. These results are consistent with the existence of Kondo like bound states of the U$^{4+}$ ionic configurations and the conduction electrons. Below the transition, these configurations are split by the development of quadrupolar ordering. The peak separation can be interpreted as a direct measurement of the order parameter. Measurements on a policrystalline UAu_2Si_2$ sample are also reported, with a comparative study of the behavior of both materials., 4 pages (Latex) + 2 postscript figures
- Published
- 1996
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