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Energy gap and proximity effect in $MgB_2$ superconducting wires | | R. Prozorov
; R. W. Giannetta
; S. L. Bud’ko
; P. C. Canfield
; | | Date: |
7 Aug 2001 | | Subject: | Superconductivity | cond-mat.supr-con | | Abstract: | Measurements of the penetration depth $lambda (T,H)$ in the presence of a DC magnetic field were performed in $MgB_2$ wires. In as-prepared wires $lambda (T,H<130 Oe)$ shows a strong diamagnetic downturn below $approx 10 K$. A DC magnetic field of $130 Oe$ completely suppressed the downturn. The data are consistent with proximity coupling to a surface $Mg$ layer left during synthesis. A theory for the proximity effect in the clean limit, together with an assumed distribution of the $Mg$ layer thickness, qualitatively explains the field and temperature dependence of the data. Removal of the $Mg$ by chemical etching results in an exponential temperature dependence for $lambda (T)$ with an energy gap of $2 Delta (0)/T_capprox 1.54$ ($Delta(0) approx 2.61 meV$), in close agreement with recent measurements on commercial powders and single crystals. This minimum gap is only 44% of the BCS weak coupling value, implying substantial anisotropy. | | Source: | arXiv, cond-mat/0108107 | | Services: | Forum | Review | PDF | Favorites | |
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