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We studied the nucleation of gold clusters on TiO2(110) surfaces in three different oxidation states by high-resolution scanning tunneling microscopy. The three TiO2(110) supports chosen were (i) reduced (having bridging oxygen vacancies), (ii) hydrated (having bridging hydroxyl groups), and (iii) oxidized (having oxygen adatoms). At room temperature, gold nanoclusters nucleate homogeneously on the terraces of the reduced and oxidized supports, whereas on the hydrated TiO2(110) surface, clusters form preferentially at the step edges. From interplay with density functional theory calculations, we identified two different gold-TiO2(110) adhesion mechanisms for the reduced and oxidized supports. The adhesion of gold clusters is strongest on the oxidized support, and the implications of this finding for catalytic applications are discussed. [ABSTRACT FROM AUTHOR]

We have grown epitaxial Pb(Zr0.2Ti0.8)O3/NdBa2Cu3O7−δ (PZT/NBCO) heterostructures and used the reversible ferroelectric polarization of Pb(Zr0.2Ti0.8)O3 to electrostatically modulate the superconducting transition of thin NdBa2Cu3O7−δ films. For ∼80 A˚ thick NdBa2Cu3O7−δ layers, reversing the ferroelectric polarization induces a 1 K change in the superconducting transition temperature. A Kosterlitz–Thouless (KT) analysis of the transitions has been used to extract the KT temperature TKT for the two polarization states. From the values obtained, one can extract the change in the zero temperature superfluid density (ns(0)). We find that the data imply a 6% change in ns(0), a value consistent with the change in carrier density produced by the ferroelectric field effect. [Copyright &y& Elsevier]

We have performed ferroelectric field effect experiments using an epitaxial heterostructure composed of ferroelectric Pb(Zr[sub 0.2]Ti[sub 0.8])O[sub 3] and superconducting Nb-doped SrTiO[sub 3]. The films were prepared on (001) SrTiO[sub 3] substrates by off-axis radio-frequency magnetron sputtering and pulsed-laser deposition. By switching the polarization field of the 500-Å-thick Pb(Zr[sub 0.2]Ti[sub 0.8])O[sub 3] layer, a large change of about 30% in resistivity and a 20% shift of T[sub c] (ΔT[sub c]∼0.05 K) were induced in the 400-Å-thick epitaxial Nb-doped SrTiO[sub 3] layer. The relationship between T[sub c] and the electrostatically modulated average carrier concentration can be mapped onto the phase diagram of chemically doped SrTiO[sub 3]. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on the electrostatic modulation of superconductivity in very thin films of cuprate superconductors using a field-effect device based on a SrTiO[sub 3] single-crystal gate insulator. A T[sub c] modulation of 3.5 K and a 37% change of the normal state resistance have been observed in an epitaxial bilayer composed of an insulating PrBa[sub 2]Cu[sub 3]O[sub 7-δ] layer deposited on top of a superconducting NdBa[sub 2]Cu[sub 3]O[sub 7-δ] film, two unit cells thick. To achieve large electric fields, the thickness of the commercial dielectric single-crystal SrTiO[sub 3] substrate (also used as the gate insulator) was reduced to 110 μm. The dielectric properties of the gate insulator were characterized as a function of temperature and electric field and the magnitude of the field effect was quantified. A T[sub c] enhancement of 2.8 K was obtained for an applied field of -1.8×10[sup 6] V/m, corresponding to a polarization of -4 μC/cm[sup 2]. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We explore the relationship between the critical temperature T(c), the mobile areal carrier density n(2D), and the zero-temperature magnetic in-plane penetration depth lambda(ab)(0) in very thin underdoped NdBa(2)Cu(3)O(7-delta) films near the superconductor to insulator transition using the electric-field-effect technique. Having established consistency with a Kosterlitz-Thouless transition, we observe that T(KT) depends linearly on n(2D), the signature of a quantum superconductor to insulator transition in two dimensions with znu(over)=1, where z is the dynamic and nu is the critical exponent of the in-plane correlation length.

We have used the ferroelectric field effect in heterostructures based on superconducting NdBa2-Cu(3)O(7-delta) and ferroelectric Pb(Zr0.2Ti0.8)O3 to electrostatically modulate in a reversible and nonvolatile fashion the hole carrier density of the superconducting layer. Reversing the ferroelectric polarization induces a constant relative change in the resistivity and Hall constant of 9% and 6%, respectively, at all temperatures above the superconducting transition. The cotangent of the Hall angle displays a T2 dependence with a slope that increases as the carrier density is reduced.