The physical properties of hybrid structures in which dissimilar materials are combined radically differ from the individual constituents’, as novel -sometimes unexpected- properties arise from the competing interactions at their interfaces. This allows engineering artificial materials with new functionalities. Oxide perovskites offer much potential for this, due to the large variety of isostructural materials available which exhibit different ground states (high-Tc superconductors, insulators, ferroics), and owing to the possibility of combining them in high-quality heterostructures.
One interesting possibility is to couple one of the heterostructure constituents’ sensitivity to external stimuli (e.g. the electrical or the magnetic field for ferroic materials) to a measurable, strongly varying physical property of the other constituent (e.g. the electrical resistance in a superconductor). We will show an example of this in the first part of the talk. We exploit the possibility for oxide superconductors of varying the superconducting critical temperature under the application of an electrostatic field. This effect is produced here in heterostructures that combine a large-polarization ferroelectric (BiFeO3) and a high-temperature superconductor (YBa2Cu3O7-d). We demonstrate that this particular system allows for an unusually large modulation of the critical temperature upon reversal of the ferroelectric polarization by the momentary application of an electric field. This enables one to effectively switch “on” and “off” high-temperature superconductivity. Furthermore, through this mechanism and owing to the ability to reversibly design the ferroelectric domain structure, we show that it is possible to produce a nanoscale modulation of the superconducting condensate. This opens new possibilities for superconducting nano-electronic devices, which may exploit flux quantization and Josephson coupling effects. [1]
Another interesting possibility is to literally merge the most distinctive property of each of the constituents in order to observe truly hybridized behaviour. In the second part of the talk, we will show an example on how to unite the long-range phase-coherent charge transport characteristic of superconductivity and the spin-polarized charge transport characteristic of ferromagnetism, which may open the door to novel spintronic devices [2]. This is demonstrated in experiments with heterostructures that combine YBa2Cu3O7-d and the half-metallic ferromagnet La0.7Ca0.3MnO3. [3]
References
[1] A. Crassous, R. Bernard, S. Fusil, K. Bouzehouane, D. Le Bourdais, S. Enouz-Vedrenne, J. Briatico, M. Bibes, A. Barthélémy, and Javier E. Villegas, Phys. Rev. Lett. 107, 247002 (2011).
[2] M. Eschrig, Phys. Today 64, 43 (2011).
[3] C. Visani, Z. Sefrioui, J. Tornos, C. León, J. Briatico, M. Bibes, A. Barthélémy, J. Santamaría and Javier E. Villegas, Nature Physics (2012) doi:10.1038/nphys2318.
Unité Mixte de physique, CNRS / Thales