Jianai Zhao

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.

Environmental reactivity characteristics of K3C60 and YBa2Cu3O7-x high-temperature superconductor thin films

Abstract Recently the environmental reactivity behavior of the copper-oxide superconductors has been studied and the following reactivity trends have been established: YBa 2 Cu 3 O 7 > Tl 2 Ba 2 Ca 2 Cu 3 O 10 > Bi 2 Sr 2 CaCu 2 O 8 ≥ La 1.85 Sr 0.15 CuO 4 > Nd 1.85 Ce 0.15 CuO 4 > Nd 1.85 Th 0.15 CuO 4 In this paper, the degradation characteristics of the most reactive cuprate material, YBa 2 Cu 3 O 7 , are compared with those of the fulleride superconductor, K 3 C 60 . Conductivity vs. exposure time measurements acquired for thin film samples in eight different environments are utilized to estimate the degradation rates for the superconductor materials. The cuprate superconductor remains relatively stable in the presence of dry nitrogen, dry oxygen, vacuum, air and acetonitrile environments, but degrades rapidly upon exposure to water solutions. Samples of K 3 C 60 are also unreactive in dry nitrogen and under vacuum, but decompose extremely rapidly upon exposure to dry oxygen, air, acetonitrile or water solutions resulting in the complete loss of the superconducting properties.

Antenna‐coupled high‐Tc bolometers for visible and near‐infrared detection using organic dyes as light‐harvesting layers

Antenna‐coupled high‐Tc bolometers fabricated from YBa2Cu3O7−δ thin films have been prepared using molecular organic dyes. Light‐harvesting layers derived from these visible and near‐infrared absorbers have been utilized to produce detectors which exhibit wavelength‐selective response characteristics in the visible and near‐infrared spectral regions. Using such hybrid structures, initial studies documenting efficient energy transfer between molecular dye layers and superconductor surfaces have been completed.

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.

Dye-coated superconductor structures as optical sensors

The preparation and characterization of a new generation of hybrid optical sensors fabricated from high-temperature superconductor thin films coated with organic dye overlayers is described herein. These dye-coated superconductor structures respond selectively to those wavelengths of light which are absorbed strongly by the molecular dye. Methods for preparing such optical sensors are details. Scanning electron microscopy, resistivity vs. temperature and optical measurements are exploited to characterize the hybrid devices.

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.

Color selective optical sensors based on dye/superconductor assemblies

This paper describes the design, construction and operation of hybrid dye/superconductor optical sensors. A reflective mirror layer positioned between the dye and superconductor components is used as a means to reject light signals that are not absorbed strongly by the dye. On resonance signals are shown to couple effectively with the underlying superconductor where they evoke measurable responses. These structures form the basis for color selective optical sensors.