Superconductivity in MgB_2 doped with Ti and C

TL;DR

This study investigates how doping MgB_2 with titanium and carbon affects its superconducting properties, revealing that C increases H_{c2} by shortening the electronic mean free path, while Ti enhances flux pinning and J_c through precipitate formation.

Contribution

It provides new insights into how Ti and C dopants improve MgB_2's superconducting performance by different mechanisms, with specific measurements of critical fields and current densities.

Findings

Carbon doping raises H_{c2} by shortening the electronic mean free path.

Titanium precipitates enhance flux pinning and increase J_c.

Co-doped MgB_2 achieves H_{c2} ~ 25 T and J_c ~ 10,000 A/cm^2 at 5 K.

Abstract

Measurements of the superconducting upper critical field, H_{c2}, and critical current density, J_c, have been carried out for MgB_2 doped with Ti and/or C in order to explore the problems encountered if these dopants are used to enhance the superconducting performance. Carbon replaces boron in the MgB_2 lattice and apparently shortens the electronic mean free path thereby raising H_c2. Titanium forms precipitates of either TiB or TiB_2 that enhance the flux pinning and raise J_c. Most of these precipitates are intra-granular in the MgB_2 phase. If approximately 0.5% Ti and approximately 2% C are co-deposited with B to form doped boron fibers and these fibers are in turn reacted in Mg vapor to form MgB_2, the resulting superconductor has H_{c2}(T=0) ~ 25 T and J_c ~ 10,000 A/cm**2 at 5 K and 2.2 T.