Steven G. Haupt

Reversible modulation of superconductivity in YBa 2 Cu 3 O 7-δ /polypyrrole sandwich structures

The preparation of a hybrid conducting polymer/high-temperature superconductor device consisting of a polypyrrole coated YBa2Cu3O7-(delta ) microbridge is reported. Electrochemical techniques are exploited to alter the oxidation state of the polymer and, in doing so, it is found that superconductivity can be modulated in a controllable and reproducible fashion by the polymer layer. Whereas the neutral (insulating) polypyrrole only slightly influences the electrical properties of the underlying YBa2Cu3O7-(delta ) film, the oxidized (conductive) polymer depresses Tc by up to 50 K. The observed reversible shifts in Tc are the largest reported to date. In a similar fashion, the oxidation state of the polymer is found to reversibly modulate the magnitude of Jc, the superconducting critical current. Thus, the operation of a molecular/superconductor switch for controlling superconductivity is demonstrated.

Organic conductor/high-Tc superconductor bilayer structures

Electrochemical techniques are exploited to fabricate conductive polymer/high Tc superconductor bilayer structures. SCanning electron microscopy and electrochemical techniques are utilized to characterize the electrodeposition of polypyrrole layers grown onto YBa2Cu3O7-(delta ) films. In such hybrid polymer/superconductor systems, it is found that when the polymer is oxidized to its conductive state, the transition temperatures (Tc) and critical currents (Jc) of the underlying superconductor film are suppressed. Reversible modulation of the values of the transition temperatures of up to 50K are noted for these structures. Upon reduction of the conductive polymer layer back to its non-conductive form, both Tc and Jc are found to return to values close to those acquired for the underivatized YBa2Cu3O7-(delta ) film. Moreover, measurements as a function of temperature of the polymer/superconductor interface resistance show dramatic decrease in this value at Tc. ALso, estimates of superconducting coherence lengths within the organic conductor samples suggest superconducting properties over macroscopically large distances within the organic materials can be expected. Collectively these results are consistent with the first observation of a conductive polymer proximity effect.

Conductive polymer/high-Tc superconductor bilayer structures

Abstract Electrochemical techniques are exploited to fabricate conductive polymer/high-T c superconductor bilayer structures. Scanning electron microscopy, x-ray fluorescence and electrochemical techniques are utilized to characterize the electrodeposition of polypyrrole layers grown onto oriented YBa 2 Cu 3 O 7 thin films. In such hybrid polymer/superconductor systems, it is found that when the polymer is oxidized to its conductive state, the transition temperature (T c ) and critical current (J c ) of the underlying superconductor film are suppressed. Here described are new methods for the fabrication of superconductor thin film layers which possess multiple points of weak electrical contact. Such weak links are very susceptible to the influence of external forces making them well suited for the creation of hybrid polymer/superconductor structures. Moreover, measurements recorded as a function of temperature of the polymer/superconductor interface resistance show dramatic decreases in resistivity at T c . Collectively, these results are consistent with observations of conductive polymer proximity effects.

Electrochemical and optical devices based on molecule/high-Tc superconductor structures

Through the use of electrochemical and vacuum deposition techniques, molecular materials are combined with high-T c superconductors in order to fabricate two new classes of hybrid devices. In the first class of devices, electrochemical methods are utilized to deposit polypyrrole onto YBa 2 Cu 3 O 7-δ structures. With such systems, experiments are conducted which explore electron transfer events which occur between the conductive polymer and the high-T c superconductor at temperatures both above and below T c . Here it is found that the transition temperature (T c ) of the superconductor is depressed dramatically when polypyrrole is oxidized to its conductive form and that it returns to a value which is close to the original value upon reduction of the polypyrrole layer to the neutral, nonconductive form. In the second class of devices, the ability of molecular dye layers to affect the optical properties of YBa 2 Cu 3 O 7-δ photodetectors is demonstrated. By examining changes in the optical and electronic properties of these systems, energy transfer processes which occur between molecules and high-T c superconductors are explored. Here it is found that dye layers are able to act as antenna for optical radiation at those wavelengths which the dye layer absorbs light most strongly.

Conductive polymer/superconductor thin film assemblies

Abstract Electrochemical procedures are utilized to deposit conductive polymer layers directly onto thin film samples of YBa2Cu3O7-δ and to cycle the polymeric structures between their neutral (non-conductive) and oxidized (conductive) forms. Through changes in the polymer doping level, the superconducting properties of the high-Tc component can be modulated in a controllable fashion. In this regard, large changes in the superconducting critical temperature and critical current values are noted as a result of the doping of the polymer layer. This paper focuses on the role of superconductor weak link structures and how such features influence the magnitude of the modulation of the superconducting properties.

Possible induction of superconductivity in conductive polymer structures

Abstract Methods for synthesizing and characterizing high-temperature superconductor/conductive polymer structures are discussed. Both chemical and electrochemical techniques are used to deposit heterocyclic polymers such as polypyrrole and poly(3-hexylthiophene) onto the cuprate materials. These hybrid systems provide the basis for the construction of the first conducting polymer/superconductor electronic device. Moreover, through the analysis of such structures the initial evidence for the induction of superconductivity into the doped conductive polymer layer is obtained.

Fabrication of organic dye-coated high-Tc superconductor optical devices: Interface chemistry and properties

The preparation and characterization of a new generation of optical sensors fabricated from high-temperature superconductor (HTSC) thin films is reported herein. These new hybrid devices are prepared using HTSC thin films which are coated with organic dye overlayers. These systems have been shown to respond selectively to those wavelengths which are absorbed strongly by the molecular dye. Methods for fabricating the superconductor element and depositing the dye layer are discussed. Moreover, scanning electron microscopy and resistivity versus temperature measurements are utilized to characterize these hybrid structures.

Molecule/High-Tc Superconductor Structures as Optical Sensors

Abstract By combining patterned high-temperature superconductor thin films with overlayers of molecular materials, a new generation of hybrid optical sensors is obtained. Here, the ability of molecular dye layers to influence the light sensing properties of a high-Tc superconducting bolometer is described. These dye-coated devices are shown to display selective optical responses which are dependent on the properties of the molecular layer. Two different types of molecular absorbing layers prepared from molecular dyes and conductive polymers are examined in this paper Furthermore, the prospects for producing wavelength tunable detectors from hybrid conducting polymer/superconductor structures are addressed.