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Bridoux, G., M. Villafuerte, J. M. Ferreyra, J. Guimpel, G. Nieva, C. A. Figueroa, B. Straube, and S. P. Heluani. "Franz-Keldysh effect in epitaxial ZnO thin films." Applied Physics Letters 112, no. 9 (2018).
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Lanoël, L., G. Rozas, A. E. Bruchhausen, L. Amigó, M. V. A. Crivillero, J. A. Hofer, M. Villafuerte, G. Bridoux, S. Bengió, and G. Nieva. "Effects of aging processes at the surface of the superconductor β−FeSe." Physical Review B 106 (2023): 214507.
Abstract: This work reports a complete analysis of surface degradation in β−FeSe single crystals; which includes the dependence on aging and temperature of Raman spectra, electrical transport resistivity, and XPS depth profiling characterization. All measurements are consistent with the emergence of clusters of Se and the presence of FeOx in the surface of the crystals. The vibrational modes of the Se clusters are coupled to the β−FeSe ones as seen in the structural transition. Moreover, this degraded surface can behave like a quasi-two-dimensional layer, as supported by a theoretical model and also consistent with Raman spectra. While the degradation of thin films of β−FeSe in air is widely known, with a corresponding loss of the superconducting properties, in single crystals with aged surfaces we observe an enhancement of the superconducting properties.
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Zapata, C., G. Nieva, J. M. Ferreyra, M. Villafuerte, L. Lanoël, and G. Bridoux. "The s-d exchange model as the underlying mechanism of magnetoresistance in ZnO doped with alkali metals." Journal of Physics: Condensed Matter 31, no. 34 (2019): 345801.
Abstract: High field magnetoresistance has been studied in epitaxial n-type ZnO:Na and ZnO:Li thin films in a temperature range between 4 K and 150 K. The resulting negative magnetoresistance can be well fitted using a semiempirical model of Khosla and Fischer based on third order contributions to the s-d exchange Hamiltonian. The parameters obtained from this model were carefully analyzed. One of these parameters is related to a ratio between electron mobilities at zero field (a non-exchange scattering mobility and an exchange or spin dependent one ). From Hall effect measurements was obtained, displaying a weak temperature dependence in accordance with highly n-doped ZnO while the extracted exhibits an anomalous T-dependence. On the other hand, our magnetoresistance data cannot be properly fitted using Kawabata’s expression based on a weak-localization model.
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