The polarization field of the ferroelectric oxide lead zirconate titanate [Pb(ZrxTi1-x)O3] was used to tune the critical temperature of the hightemperature superconducting cuprate gadolinium barium copper oxide (GdBa2Cu3O7-x) in a reversible, nonvolatile fashion. For slightly underdoped samples, a uniform shift of several Kelvin in the critical temperature was observed, whereas for more underdoped samples, an insulating state was induced. This transition from superconducting to insulating behavior does not involve chemical or crystalline modification of the material.

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7. A. Carillon eta/. . ibid. 68, 291 7 (1 992) 8. J A. Koch eta/. . ibid p 3291 9. L. B. Da S v a ei a/. , Opt Lett. 18, 11 74 (1 993).