Electrochemical Tuning of Metal Insulator Transition and Nonvolatile Resistive Switching in Superconducting Films

Anna Palau*,Alejandro Fernandez-RodriguezJuan Carlos Gonzalez-RosilloXavier GranadosMariona CollBernat BozzoRafael Ortega-HernandezJordi SuñéNarcís MestresXavier Obradors, and Teresa Puig. ACS Appl. Mater. Interfaces, 2018, 10 (36), pp 30522–30531.

DOI: 10.1021/acsami.8b08042

Modulation of carrier concentration in strongly correlated oxides offers the unique opportunity to induce different phases in the same material, which dramatically change their physical properties, providing novel concepts in oxide electronic devices with engineered functionalities. This work reports on the electric manipulation of the superconducting to insulator phase transition in YBa2Cu3O7−δ thin films by electrochemical oxygen doping. Both normal state resistance and the superconducting critical temperature can be reversibly manipulated in confined active volumes of the film by gate-tunable oxygen diffusion. Vertical and lateral oxygen mobility may be finely modulated, at the micro- and nano-scale, by tuning the applied bias voltage and operating temperature thus providing the basis for the design of homogeneous and flexible transistor-like devices with loss-less superconducting drain–source channels. We analyze the experimental results in light of a theoretical model, which incorporates thermally activated and electrically driven volume oxygen diffusion.

Angular flux creep contributions in YBa2Cu3O7−δ nanocomposites from electrical transport measurements

F. Vallès, A. Palau, V. Rouco, B. Mundet, X. Obradors & T. Puig. Scientific Reports, volume 8, Article number: 5924(2018). 

doi:10.1038/s41598-018-24392-1

Flux magnetic relaxation (flux creep) causes logarithmic decay on the critical currents in superconductors, especially at high temperatures, in detriment of applications for high temperature superconductors. In this work, we present a novel methodology to measure the flux creep rate in YBCO from electrical transport measurements instead of using traditional magnetic relaxation measurements. This new methodology provides a faster way to analyze creep and enables to expand the analysis to any orientation of the magnetic field. In particular, we have applied this analysis to study the creep rate in chemical solution deposited nanocomposites (YBCO with included nanoparticles), revealing that emerging stacking faults provide flux pinning and additionally reduce the flux magnetic relaxation.

Disentangling vortex pinning landscape in chemical solution deposited superconducting YBa2Cu3O7−x films and nanocomposites

A Palau, F Vallès, V Rouco, M Coll, Z Li, C Pop, B Mundet, J Gàzquez, R Guzman, J Gutierrez, X Obradors and T Puig. Superconductor Science and TechnologyVolume 31Number 3https://doi.org/10.1088/1361-6668/aaa65e

In-field angular pinning performances at different temperatures have been analysed on chemical solution deposited (CSD) YBa2Cu3O7−x (YBCO) pristine films and nanocomposites. We show that with this analysis we are able to quantify the vortex pinning strength and energies, associated with different kinds of natural and artificial pinning defects, acting as efficient pinning centres at different regions of the H–T phase diagram. A good quantification of the variety of pinning defects active at different temperatures and magnetic fields provides a unique tool to design the best vortex pinning landscape under different operating conditions. We have found that by artificially introducing a unique defect in the YBCO matrix, the stacking faults, we are able to modify three different contributions to vortex pinning (isotropic-strong, anisotropic-strong, and isotropic-weak). The isotropic-strong contribution, widely studied in CSD YBCO nanocomposites, is associated with nanostrained regions induced at the partial dislocations surrounding the stacking faults. Moreover, the stacking fault itself acts as a planar defect which provides a very effective anisotropic-strong pinning at H//ab. Finally, the large presence of Cu–O cluster vacancies found in the stacking faults have been revealed as a source of isotropic-weak pinning sites, very active at low temperatures and high fields.

Tunable Self-Assembly of YF3 Nanoparticles by Citrate-Mediated Ionic Bridges

Jordi Martínez-Esaín, Jordi Faraudo*, Teresa Puig, Xavier Obradors, Josep Ros, Susagna Ricart, and Ramón Yáñez*. J. Am. Chem. Soc., Article ASAP. DOI: 10.1021/jacs.7b09821

Ligand-to-surface interactions are critical factors in surface and interface chemistry to control the mechanisms governing nanostructured colloidal suspensions. In particular, molecules containing carboxylate moieties (such as citrate anions) have been extensively investigated to stabilize metal, metal oxide, and metal fluoride nanoparticles. Using YF3 nanoparticles as a model system, we show here the self-assembly of citrate-stabilized nanostructures (supraparticles) with a size tunable by temperature. Results from several experimental techniques and molecular dynamics simulations show that the self-assembly of nanoparticles into supraparticles is due to ionic bridges between different nanoparticles. These interactions were caused by cations (e.g., ammonium) strongly adsorbed onto the nanoparticle surface that also interact strongly with nonbonded citrate anions, creating ionic bridges in solution between nanoparticles. Experimentally, we observe self-assembly of nanoparticles into supraparticles at 25 and 100 °C. Interestingly, at high temperatures (100 °C), this citrate-bridge self-assembly mechanism is more efficient, giving rise to larger supraparticles. At low temperatures (5 °C), this mechanism is not observed, and nanoparticles remain stable. Molecular dynamics simulations show that the free energy of a single citrate bridge between nanoparticles in solution is much larger than the thermal energy and in fact is much larger than typical adsorption free energies of ions on colloids. Summarizing our experiments and simulations, we identify as key aspects of the self-assembly mechanism the requirement of NPs with a surface able to adsorb anions and cations and the presence of multidentate ions in solution. This indicates that this new ion-mediated self-assembly mechanism is not specific of YF3 and citrate anions, as supported by preliminary experimental results in other systems.

Institut de Ciència de Materials de Barcelona ICMAB CSIC

Address


Campus de la UAB, 08193 Bellaterra, Barcelona, Spain
+34 935 801 853 ext 371 
hr_suman@icmab.es