arXiv subjects

R. F. Luccas

Publications and source records attributed to R. F. Luccas.

5 recordsLinked to original sources

arXiv2026

Improving YBa$_2$Cu$_3$O$_{7-δ}$ annealing times through a combining-temperatures route

The oxygenation process at constant temperature of YBa$_2$Cu$_3$O$_{7-δ}$ (YBCO) was systematically investigated in the temperature range from 300 $^o$C to 800 $^o$C. With this purpose, fully deoxygenated powder samples was exposed to an oxygen saturated atmosphere, and the evolution of their mass was recorded as a function of time using a thermogravimetric balance. Results reveal a strong dependence of both: the oxygenation kinetics and the final oxygen saturation level, on the temperature used for oxygenation. Moreover, results show that higher oxygen temperatures promote faster oxygen absorption but lead to lower saturation levels (higher final $δ$ values), whereas lower oxygen temperatures result in slower kinetics but enable the system to approach better oxygenation conditions in order to improve the final superconducting properties of the material. In addition to our measurements, a comparative analysis between oxygenation levels at the oxygen temperatures under study was performed in the range around oxygen saturation ($δ$ $<$ 0.3). Consequently, an oxygenation protocol based on a combination of several oxygenation temperatures is proposed. As a first approach, results from a protocol with just two different oxygenation temperatures is compared with results coming from using just one oxygenation temperature. Outstandingly, a protocol with a first oxygenation step at high temperatures and a second one at low temperatures demonstrates to improve oxygenation times in near a 30 \% for reaching $δ$ values below 0.1 and in near a 60 \% for reaching $δ$ values around 0.12. Finally, we trust that our results are of direct application on industry since size of grain used herein are in scales of typical thickness of superconductor tapes.

cond-mat.supr-con↗

arXiv2022

CDW signatures in the electronic structure of LaSb2 at 13 K and metal-insulator transition

Light rare-earth antimonide LaSb2 is a material susceptible to nesting and exhibits a Charge Density Wave (CDW) at 355 K as well as superconductivity below 1.2 K. In the seek for additional CDW transitions, we have studied the temperature-dependent of LaSb2 at 200 and 13 K and infer CDW manifestations by combining angle-resolved photoemission spectroscopy (ARPES) measurements and density functional theory (DFT) calculations. ARPES measurements at 200 K show a metallic system while it appears to be semiconducting at 13 K, at odds with existing resistivity measurements. At 13 K, ARPES shows the band folding of the inner Fermi surface pockets, with considerable spectral weight on the folded band. We find a nesting vector at q = 0.25$\pm$0.02 Å -1. In addition, we observe Umklapps of other bands due to the onset of the new periodicity, together with a semiconducting behavior in the whole reciprocal space. Calculations demonstrate that the folded band is associated with the La-Sb layer and that in-plane distortion is the most probable structural modification in the system, probably affecting the whole unit cell.

cond-mat.mtrl-sci↗

arXiv2015

Proximity driven commensurate pinning in YBa2Cu3O7 through all-oxide magnetic nanostructures

The design of artificial vortex pinning landscapes is a major goal towards large scale applications of cuprate superconductors. While disordered nanometric inclusions have shown to modify their vortex phase diagram and to produce enhancements of the critical current1,2, the effect of ordered oxide nanostructures remains essentially unexplored. This is due to the very small nanostructure size imposed by the short coherence length, and to the technological difficulties in the nanofabrication process. Yet, the novel phenomena occurring at oxide interfaces open a wide spectrum of technological opportunities to interplay with the superconductivity in cuprates. Here we show that the unusual long range suppression of the superconductivity occurring at the interface between manganites and cuprates affects vortex nucleation and provides a novel vortex pinning mechanism. In particular, we show evidence of commensurate pinning in YBCO films with ordered arrays of LCMO ferromagnetic nanodots. Vortex pinning results from the proximity induced reduction of the condensation energy at the vicinity of the magnetic nanodots, and yields an enhanced friction between the nanodot array and the moving vortex lattice in the liquid phase. This result shows that all-oxide ordered nanostructures constitute a powerful, new route for the artificial manipulation of vortex matter in cuprates.

cond-mat.supr-con↗

arXiv2015

Magnetic field dependence of the density of states in the multiband superconductor $β$-Bi$_2$Pd

We present very low temperature scanning tunneling microscopy (STM) experiments on single crystalline samples of the superconductor $β$-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 $β$-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.

cond-mat.supr-con↗

arXiv2013

Superconductivity and magnetism on flux grown single crystals of NiBi3

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.

cond-mat.supr-con↗