Energy gap and proximity effect in $Mg{B}_2$ superconducting wires

Abstract

Measurements of the penetration depth $\lambda (T,H)$ in the presence of a DC magnetic field were performed in $Mg{B}_2$ wires. In as-prepared wires $\lambda (T,H<130Oe)$ shows a strong diamagnetic downturn below $\approx 10K$. A DC magnetic field of $130Oe$ 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 $2\Delta (0)/T_c\approx 1.54$ ($\Delta (0)\approx 2.61meV$), 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.

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References in corpus (9)

• Boron Isotope Effect in Superconducting MgB${}_2$
• Superconductivity in Dense $Mg{B}_2$ Wires
• Scanning Tunneling Spectroscopy in MgB2
• Tunneling spectroscopy in small grains of superconducting MgB2
• High-Resolution Photoemission Study of MgB2
• Energy Gap from Tunneling and Metallic Sharvin Contacts onto MgB2: Evidence for a Weakened Surface Layer
• Tunneling spectroscopy measurement of the superconductor gap parameter of MgB_2
• Optical conductivity and penetration depth in MgB2
• Penetration Depth Measurements in MgB_2: Evidence for Unconventional Superconductivity

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