Person:
Cuéllar Jiménez, Fabian Andrés

First Name

Fabian Andrés

Last Name

Cuéllar Jiménez

URI

https://hdl.handle.net/20.500.14352/75052

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Físicas

Department

Física de Materiales

Area

Física Aplicada

Identifiers

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Now showing 1 - 10 of 25

Magnetic field influence on the proximity effect at YBa_(2)Cu_(3)O_(7)/La_(2/3)Ca_(1/3)MnO_(3) superconductor/half-metal interfaces
(Physical review B, 2015) Visani, C.; Cuéllar Jiménez, Fabian Andrés; Pérez Muñoz, Ana Mª; Sefrioui, Zouhair; León Yebra, Carlos; Santamaría Sánchez-Barriga, Jacobo; Villegas, Javier E.
We experimentally study the superconducting proximity effect in high-temperature superconductor/halfmetallic ferromagnet YBa_(2)Cu_(3)O_(7)/La_(2/3)Ca_(1/3)MnO_(3) junctions, using conductance measurements. In particular, we investigate the magnetic-field dependence of the spectroscopic signatures that evidence the long-range penetration of superconducting correlations into the half-metal. Those signatures are insensitive to the applied field when this is below the ferromagnet’s saturation fields, which demonstrates that they are uncorrelated with its macroscopic magnetization. However, the application of more intense fields progressively washes away the fingerprint of long-range proximity effects. This is consistent with the fact that the well-known magnetic inhomogeneities at the c-axis YYBa_(2)Cu_(3)O_(7)/La_(2/3)Ca_(1/3)MnO_(3) interface play a role in the proximity behavior.
Long-range superconducting proximity effect in YBa2Cu3O7/La0.7Ca0.3MnO3 weak-link arrays
(Applied Physics Letters, 2024) Sánchez Manzano, David; Mesoraca, S.; Rodríguez Corvillo, Sara; Lagarrigue, A.; Gallego Toledo, Fernando; Cuéllar Jiménez, Fabian Andrés; Sander, A.; Rivera Calzada, Alberto Carlos; Valencia, S.; Villegas, J.E.; León Yebra, Carlos
The interplay between ferromagnetism and superconductivity has attracted substantial interest due to its potential for exotic quantum phenomena and advanced electronic devices. Although ferromagnetism and superconductivity are antagonistic phenomena, ferromagnets (F) can host spin-triplet superconductivity induced via proximity with superconductors (S). To date, most of the experimental effort has been focused on single S/F/S junctions. Here, we have found the fingerprints of long-range superconducting proximity effect in micrometric weaklink arrays, formed by embedding YBa2Cu3O7 superconducting islands in a half-metallic ferromagnet La0.7Ca0.3MnO3 film. These arrays show magnetoresistance oscillations that appear at temperatures below the critical temperature of YBa2Cu3O7 for currents below a threshold, indicating their superconducting origin. This realization paves the way for device architectures displaying macroscopic quantum interference effects, which are of interest for field sensing applications, among others.
All manganite tunnel junctions with interface induced barrier magnetism
(Advanced Materials, 2010) Sefrioui Khamali, Zouhair; Rivera Calzada, Alberto Carlos; León Yebra, Carlos; Cuéllar Jiménez, Fabian Andrés; Santamaría Sánchez-Barriga, Jacobo; Barthélémy, A.; Sefrioui Khamali, Zouhair
In epitaxial heterostructures combining strongly correlated manganese oxides with antiferromagnetic-insulator or half-metallic character, a large interfacial moment is found and used to produce a spin-filter-like behavior in all-manganite tunnel junctions. The results suggest that after playing a key role in exchange-bias for spin-valves, uncompensated moments at engineered antiferromagnetic interfaces represent a novel route for generating highly spin-polarized currents with antiferromagnets.
Capítulo VII. Discovering the smartphone magnetometers of an experiment-based exam
(Nuevas estrategias, uso de las TIC y creación de espacios para la innovación educativa, 2023) Cuéllar Jiménez, Fabian Andrés; Farfán Montero, Juana; Ramé López Jesús; Souto-Rico, Mónica
Conventionally, the final exam for the Laboratory of Electricity and Magnetism in the Physics Degree at the Universidad Complutense de Madrid consisted of a written exam, which was focused on replacing numerical values on equations that students should memorize. We consider this to be an outdated approach and have replaced this exam (for one call) with a practical problem that emphasizes the design of an experiment, comprehension of concepts, and the ability to apply them to real problems, rather than giving a higher weight to memory and arithmetic capabilities. We replaced this written exam with a practical problem that focused on experimental understanding and application of magnetic fields, the Hall Effect, the Biot-Savart Law, and the scientific method. The practical used sensors from a smartphone to design a "Biot-Savart" experiment that could be implemented during remote teaching scenarios. Students designed experiments, performed measurements, and presented their findings. The activity consisted of two major parts. The first part aimed to find the three magnetometers in the selected smartphone, assess the measurement range, and identify the measurement direction of each of them. The second part involved calculating the magnetic field generated by a single wire loop using the Biot-Savart Law, followed by constructing and measuring the loop. The activity evaluation graded the processes of design, measurement, and analysis, rather than the numerical outcome of each case. Moreover, it is not possible to expect students to have a current source at home; hence, the numerical outcome of the Biot-Savart law loses its relevance. This activity aimed to exercise the following abilities: teamwork, thinking and applying design, technological application (use of smartphones), and report writing (explaining the design and writing result reports). A survey of 100 students showed that 51% considered this methodology a better learning approach than the traditional written exam, and 75% found it more adapted to evaluate the targeted abilities. Despite the long activity, 56% of students received grades above 9.3 due to their correct application of concepts. This innovative methodology positively affected students' involvement and motivation for the learning process, and is a work in progress. We consider that this methodology constitutes an innovative procedure with room for improvement, which is positively received by the students, increasing their involvement and motivation for the learning process.
Large magnetoresistance of isolated domain walls in La_(0.7)Sr(0.3)MnO_3 nanowires
(Advanced Materials, 2023) Orfila Rodríguez, Gloria; Sanchez-Manzano, David; Arora, Ashima; Cuéllar Jiménez, Fabian Andrés; Ruiz Gómez, Sandra; Rodriguez-Corvillo, Sara; López, Sandra; Peralta, Andrea; Carreira, Santiago J.; Gallego, Fernando; Tornos Castillo, Javier; Rouco Gómez, Víctor; Riquelme, Juan J.; Munuera, Carmen; Mompean, Federico J.; Garcia-Hernandez, Mar; Sefrioui Khamali, Zouhair; Villegas Hernández, Javier Eulogio; Pérez García, Lucas; Rivera Calzada, Alberto Carlos; León Yebra, Carlos; Valencia, Sergio; Santamaría Sánchez-Barriga, Jacobo
Generation, manipulation, and sensing of magnetic domain walls are cornerstones in the design of efficient spintronic devices. Half-metals are amenable for this purpose as large low field magnetoresistance signals can be expected from spin accumulation at spin textures. Among half metals, La1−xSrxMnO3 (LSMO) manganites are considered as promising candidates for their robust half-metallic ground state, Curie temperature above room temperature (Tc = 360 K, for x = 1/3), and chemical stability. Yet domain wall magnetoresistance is poorly understood, with large discrepancies in the reported values and conflicting interpretation of experimental data due to the entanglement of various source of magnetoresistance, namely, spin accumulation, anisotropic magnetoresistance, and colossal magnetoresistance. In this work, the domain wall magnetoresistance is measured in LSMO cross-shape nanowires with single-domain walls nucleated across the current path. Magnetoresistance values above 10% are found to be originating at the spin accumulation caused by the mistracking effect of the spin texture of the domain wall by the conduction electrons. Fundamentally, this result shows the importance on non-adiabatic processes at spin textures despite the strong Hund coupling to the localized t2g electrons of the manganite. These large magnetoresistance values are high enough for encoding and reading magnetic bits in future oxide spintronic sensors.
Magnetic tunnel junctions based on complex oxides
(2013) Cuéllar Jiménez, Fabian Andrés; Sefrioui, Zouhair; León Yebra, Carlos
Extremely long-range, high-temperature Josephson coupling across a half-metallic ferromagnet
(Nature Materials, 2022) Sanchez Manzano, David; Cuéllar Jiménez, Fabian Andrés; Cabero Piris, Mariona; Rouco Gómez, Víctor; Orfila Rodríguez, Gloria; Tornos Castillo, Javier; Rivera Calzada, Alberto Carlos; González Calbet, José María; León Yebra, Carlos; Villegas Hernández, Javier Eulogio; Santamaría Sánchez-Barriga, Jacobo
The Josephson effect results from the coupling of two superconductors across a spacer such as an insulator, a normal metal or a ferromagnet to yield a phase coherent quantum state. However, in junctions with ferromagnetic spacers, very long-range Josephson effects have remained elusive. Here we demonstrate extremely long-range (micrometric) high-temperature (tens of kelvins) Josephson coupling across the half-metallic manganite La0.7Sr0.3MnO3 combined with the superconducting cuprate YBa2Cu3O7. These planar junctions, in addition to large critical currents, display the hallmarks of Josephson physics, such as critical current oscillations driven by magnetic flux quantization and quantum phase locking effects under microwave excitation (Shapiro steps). The latter display an anomalous doubling of the Josephson frequency predicted by several theories. In addition to its fundamental interest, the marriage between high-temperature, dissipationless quantum coherent transport and full spin polarization brings opportunities for the practical realization of superconducting spintronics, and opens new perspectives for quantum computing. Josephson coupling over micrometres and at tens of kelvins is demonstrated across the half-metallic manganite La0.7Sr0.3MnO3 combined with the superconducting cuprate YBa2Cu3O7.
Disentangling photodoping, photoconductivity, and photosuperconductivity in the cuprates
(Physical Review Letters, 2024) El Hage, R.; Sánchez Manzano, David; Humbert, V.; Carreira, S.; Rouco Gómez, Víctor; Sander, A.; Cuéllar Jiménez, Fabian Andrés; Seurre, K.; Lagarrigue; S. Mesoraca, A.; Briatico, J.; Trastoy, J.; Santamaría Sánchez-Barriga, Jacobo; Villegas, J. E.
The normal-state conductivity and superconducting critical temperature of oxygen-deficient YBa2Cu3O7-delta can be persistently enhanced by illumination. Strongly debated for years, the origin of those effects-termed persistent photoconductivity and photosuperconductivity (PPS)-has remained an unsolved critical problem, whose comprehension may provide key insights to harness the origin of hightemperature superconductivity itself. Here, we make essential steps toward understanding PPS. While the models proposed so far assume that it is caused by a carrier-density increase (photodoping) observed concomitantly, our experiments contradict such conventional belief: we demonstrate that it is instead linked to a photo-induced decrease of the electronic scattering rate. Furthermore, we find that the latter effect and photodoping are completely disconnected and originate from different microscopic mechanisms, since they present different wavelength and oxygen-content dependences as well as strikingly different relaxation dynamics. Besides helping disentangle photodoping, persistent photoconductivity, and PPS, our results provide new evidence for the intimate relation between critical temperature and scattering rate, a key ingredient in modern theories on high-temperature superconductivity.
Thermally assisted tunneling transport in La_(0.7)Ca_(0.3)MnO_(3)/SrTiO_(3):Nb Schottky-like heterojunctions
(Physical review B, 2012) Cuéllar Jiménez, Fabian Andrés; Sánchez Santolino, Gabriel; Varela Del Arco, María; Clement, M.; Iborra, E.; Sefrioui, Zouhair; Santamaría Sánchez-Barriga, Jacobo; León Yebra, Carlos
We report on the electrical transport properties of all-oxide La_(0.7)Ca_(0.3)MnO_(3)/SrTiO_(3):Nb heterojunctions with lateral size of just a few micrometers. The use of lithography techniques to pattern manganite pillars ensures perpendicular transport and allows exploration of the microscopic conduction mechanism through the interface. From the analysis of the current-voltage characteristics in the temperature range 20–280 K we find a Schottky-like behavior that can be described by a mechanism of thermally assisted tunneling if a temperature-dependent value of the dielectric permittivity of SrTiO_(3):Nb (NSTO) is considered. We determine the Schottky energy barrier at the interface, qVB = 1.10 ± 0.02 eV, which is found to be temperature independent, and a value of ξ = 17 ± 2 meV for the energy of the Fermi level in NSTO with respect to the bottom of its conduction band.
Electron Doping by Charge Transfer at LaFeO_3 /Sm_2CuO_4 Epitaxial Interfaces
(Advanced Materials, 2013) Bruno, Flavio Yair; Schmidt, Rainer; Varela Del Arco, María; Garcia Barriocanal, Javier; Rivera Calzada, Alberto Carlos; Cuéllar Jiménez, Fabian Andrés; León Yebra, Carlos; Thakur, Pardeep; Cezar, Julio C.; Brookes, Nicholas B.; Garcia-Hernandez, Mar; Dagotto, Elbio; Pennycook, Stephen J.; Santamaría Sánchez-Barriga, Jacobo
Using X-ray absorption spectroscopy and electron energy loss spectroscopy with atomic-scale spatial resolution, experimental evidence for charge transfer at the interface between the Mott insulators Sm2CuO4 and LaFeO3 is obtained. As a consequence of the charge transfer, the Sm2CuO4 is doped with electrons and thus epitaxial Sm2CuO4/LaFeO3 heterostructures become metallic.