Field Effect Studies of Correlated Oxides :

In the area of field effect in correlated oxides and superconductors, we try to modulate the electronic properties using electrostatics. One of the fascinating challenges is that most of the correlated electron systems are very sensitive to numerous parameters including the carrier density (which can be modulated by the field effect). As shown on the Figure, depending on the carrier density, these materials can be insulating, conducting or superconducting. Field effect in correlated oxide systems thus opens many interesting opportunities from the fundamental and applied point of view.

Behaviour of different materials as a function of their 2D sheet carrier density. As can be seen, for instance for the high Tc superconductors, the material can be, depending on its carrier density, insulating, metallic, or superconducting.

The challenges in this field have been recently reviewed :

Related papers :

• Electrostatic modification of novel materials
  C. H. Ahn, A. Bhattacharya, M. Di Ventra, J. N. Eckstein, C. Daniel Frisbie, M. E. Gershenson, A. M. Goldman, I. H. Inoue, J. Mannhart, Andrew J. Millis, Alberto F. Morpurgo, Douglas Natelson, and Jean-Marc Triscone
  Reviews of Modern Physics 78, 1185 (2006).



• Electric field effect in correlated oxide systems
  C. H. Ahn, J.-M. Triscone and J. Mannhart
  Nature 424, 1015 (2003).

ONGOING PROJECTS

• Field effect close to the S-I transition in underdoped high Tc films


• electronic writing in doped Nb-SrTiO3 superconducting films


• Ferroelectric field effect in manganite thin films

Field effect close to the S-I transition in underdoped high Tc films.

In this work we explore the Temperature – Doping high Tc phase diagram very close to the superconductor – insulator transition using electric field effect. In very underdoped films of NdBa2Cu3O7-delta we show, tuning electrostatically the carrier density, that Tc is proportional to the carrier density and to the inverse penetration depth square suggesting that the system experiences a 2D QSI transition.

Resistivity vs temperature for a 3-4 unit cells thick NBCO film for different applied gate voltages.

Local electronic writing in doped Nb-SrTiO3 superconducting films.

Here, we have developed a model system combining Nb doped SrTiO3, a low Tc superconductor, and ferroelectric PZT. We demonstrate large shifts in Tc and the possibility to modify locally the electronic properties of doped SrTiO3.

Resistivity versus temperature at low temperatures in Nb:SrTiO₃. A super-conducting on-off switching is observed around 270 mK.

Related papers :

• Local switching of two-dimensional superconductivity using the ferroelectric field effect
  K. S. Takahashi, M. Gabay, D. Jaccard, K. Shibuya, T. Ohnishi, M. Lippmaa and J.-M. Triscone
  Nature 441, 195 (2006).

Ferroelectric field effect in manganite thin films.

In this project in collaboration with Charles Ahn at Yale University, we try probing electric field induced changes in the ferromagnetic properties of very thin manganite films using a home developed MOKE technique.

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