Superconductor-insulator transition and electric field effect of YyPr1−yBa2Cu3O7−x thin films

Abstract

The transport characteristics of Y y Pr 1Ϫy Ba 2 Cu 3 O 7Ϫx thin film systems were systematically investigated as a function of the Y concentration and film thickness. The films in the superconducting state changed their transport characteristics to those of the nonsuperconducting state when the film thickness was decreased beyond the value at which the film sheet resistance is equal to the quantized sheet resistance h/4e 2 . This phenomenon is a kind of superconductor-insulator transition. The resistance-temperature characteristics in the insulator phase are a result of the variable-range-hopping conduction between localized states. The electric-field effect was measured especially in the insulator phase. The resistance modulation ratio ⌬R/R in the insulator phase was much greater than the carrier density modulation ratio ⌬N/N. The ratio of ⌬R/R to ⌬N/N increased as the Y concentration increased. In particular, the (⌬R/R)/(⌬N/N) value reached as high as 50 for a Y 0.9 Pr 0.1 Ba 2 Cu 3 O 7Ϫx film in the insulator phase. Higher (⌬R/R)/ (⌬N/N) values effectively enhance the performance of superconducting field effect transistors.

Superconducting properties of ultrathin Bi2Sr2CaCu2O8+x single crystals

“…4, and we see that the boundary value for S-I transition in our samples is consistent with R q . Similar S-I transition was also observed in other HTS ultrathin films [8,23,24].…”

Conductivity of weakly insulating amorphous nickel - silicon films below the metal - insulator transition

“…In contrast, the conductivity of a 3D metallic film at sufficiently low temperatures can be described by a power-law expression σ (T ) = σ (0) + CT z (5) where σ (0) is the finite zero-temperature conductivity, C is a prefactor and z is the exponent of the temperature power law. Equation ( 5) might approximate the conductivity contributions of the 3D EEI theory [15] and/or of the 3D WL theory [16].…”

“…The approach to the metal-insulator transition (MIT) from the metallic side in twodimensional (2D) systems has been studied experimentally by many groups [1][2][3][4][5]. A good summary of the experimental results on the metallic side of the MIT can be found in Belitz and Kirkpatrick's review article [6] and Castners review paper [7].…”

“…Many studies have been made on thin 2D films [1][2][3][4][5]; interpretation of the metalinsulator transition is complicated in 2D systems by superconductivity and by the strength of the spin-orbit interaction that enters in the weak localization theory calculations. In the normal state, thin 2D films are expected to be insulating owing to the ln T dependence of the EEI contribution [15] and of the weak localization (WL) contribution to the conductivity [16].…”

Correlación entre la superconductividad y la estructura en el sistema [Y1−xPrx]Ba2Cu3O7

“…On the other hand, the electronic properties in high Tc superconducting compounds are indeed very important because they define the superconducting properties in order to enhance the applicability of these materials [7,8]. The electronic bands states in the electronic structure are very sensitive to short-range order in the atomic positions [5].…”