Critical fields and critical currents in MgB₂

Abstract

We review recent measurements of upper (Hc2) and lower (Hc1) critical fields in clean single crystals of MgB2, and their anisotropies between the two principal crystallographic directions. Such crystals are far into the ‘clean limit’ of type II superconductivity, and indeed for fields applied in the c-direction, the Ginzburg–Landau parameter κ is only about 3, just large enough for type II behaviour. Because μ0 Hc2 is so low, about 3 T for fields in the c-direction, MgB2 has to be modified for it to become useful for high-current applications. It should be possible to increase Hc2 by the introduction of strong electron scattering (but because of the electronic structure and the double gap that results, the scatterers will have to be chosen carefully). In addition, pinning defects on a scale of a few nm will have to be engineered in order to enhance the critical current density at high fields.

Significant improvement of activation energy in MgB2∕Mg2Si multilayer films

“…14,15 The Ginzburg-Landau ͑GL͒ coherence length ͑0͒ is about 10 nm within a-b plane and 5 nm along c axis for MgB 2 . 16 Because that the coupling between B layers in MgB 2 ͑c = 0.352 nm͒ are strong, the superconductor is not expected to display intrinsic two-dimensional pancake vortices that have been predicted in HTS. 17 In this letter, we show that using sequential pulsed laser deposition ͑PLD͒, an artificially multilayered structure has been achieved with the aid of an off-axis deposition method.…”

Transport properties of multilayered MgB2∕Mg2Si superconducting thin film

“…14,15 The Ginzburg-Landau ͑GL͒ coherence length ͑0͒ is about 10 nm within the a-b plane and 5 nm along the c axis for MgB 2 . 16 Because the coupling between the B layers in MgB 2 ͑c = 0.352 nm͒is strong, the superconductor does not display the intrinsic two dimensional pancake vortices that have been observed in HTSs. 17 Mg 2 Si is a very stable semiconductor and can be easily formed from Mg+ Si at a temperature as low as 200°C.…”

X-ray Micro-Tomography as a New and Powerful Tool for Characterization of MgB2 Superconductor

“…Ginzburg-Landau coherence length along the ab-plane is ξ ab = 10 nm, while along c-axis is ξ c = 5 nm [5]. These values are significantly higher than for the HTS resulting in transparent grain boundaries for the supercurrent passing.…”