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Asymmetry between flux penetration and flux expulsion in Tl-2212 superconductors (1993)

Foldeaki, M. ; Ledbetter, H. ; Paranthaman, M. ; [et al.]

Springer

Journal of superconductivity 6 (1993), S. 185-189

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ISSN: 1572-9605

Keywords: Thallium cuprates ; superconductivity ; magnetic hysteresis ; irreversibility ; flux pinning

Source: Springer Online Journal Archives 1860-2000

Topics: Electrical Engineering, Measurement and Control Technology , Physics

Notes: Abstract dc magnetic hysteresis as well as flux penetration and flux expulsion were investigated in Tl2−y Ba2CaCu2O8−x polycrystals and monocrystals. All measurements were performed at 35 K and in the 0–5 T field range. Hysteresis measurements revealed an irreversibility field of about 2 T. Existing models predict identical field-cooled (fc) and zero-field-cooled (zfc) magnetizations and vanishing time dependence above this field. Although the identical fc and zfc magnetizations are in fact observed, the time dependence vanishes only for flux penetration after zero-field cooling; a remanence is preserved after field cooling and decays with a finite relaxation rate. Activation energies calculated on the basis of the thermal activation model display a pronounced field dependence, and arelower for flux penetration than for flux expulsion in high fields (H≥3 T) for all orientations. This behavior of extreme layered superconductors contradicts classical theoretical models and questions the original definition of the irreversibility line as well. All of our results are consistent with the recent theory of lock-in transition, and can be well interpreted by using those principles.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00625745

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Charge transfer complexes of N-ethylcarbazole and poly-N-vinylcarbazole (1968)

Rembaum, A. ; Hermann, A. M. ; Haack, R.

New York : Wiley-Blackwell

Journal of Polymer Science Part A-1: Polymer Chemistry 6 (1968), S. 1955-1963

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ISSN: 0449-296X

Keywords: Physics ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: Poly-N-vinylcarbazole and its monomeric analog, i.e., N-ethylcarbazole, act as donors in charge transfer complexes with such electron acceptors as iodine, tetracyanoethylene, and tetracyanoquinodimethane. Poly-N-vinylcarbazole and N-ethylcarbazole are also capable of accepting electrons from an alkali metal such as sodium. A study of the spectral properties of both types of complexes showed that the monomer can both accept and donate electrons to a greater extent than the corresponding unit segment of the polymer chain. Equilibrium constants are presented for both cases, and estimates of the ionization potential of N-ethylcarbazole and related compounds are made from the characteristic charge transfer frequencies. Good agreement between these values and those calculated from molecular orbital theory is outlined.

Additional Material: 4 Ill.