MgB₂thin films

Abstract

Great progress has been made in the deposition of MgB2 thin films since the discovery of superconductivity at 39 K in this two-band superconductor. In this review, deposition techniques used for MgB2 are described, with an emphasis on their meeting the critical requirements for growing high-quality MgB2 thin films. The availability of these thin films has contributed significantly to the research on the two-gap superconductivity in MgB2. MgB2 thin films have also been investigated for applications in high-field magnets, superconducting electronic devices and circuits, and radio-frequency cavities used in accelerators.

Superconducting magnesium diboride coatings for radio frequency cavities fabricated by hybrid physical-chemical vapor deposition

“…The residual resistivity ratios of the three measured films lie in the range from 3.5 to 7. These values are comparable to properties obtained from samples fabricated using the regular HPCVD setup [6,7,30]. The middle sample consistently shows better properties, including higher T c , lower resistivity, and smaller surface roughness, suggesting that it is important to restrict the diborane gas mixture and Mg vapor inside the stainless steel tube in order to create a uniform gas flow pattern.…”

“…The superconducting transition temperature of MgB 2 is around 39 K, significantly higher than Nb (9.2 K). Its lower residual resistivity [6] and larger thermodynamic critical field [7][8][9] make it a promising candidate for SRF cavity coatings. According to Collings et al [5], MgB 2 -coated cavities can potentially exhibit a higher superheating critical field H sh than that of Nb, and as a result, a much higher E acc would be imaginable [10].…”

Enhancement of lower critical field by reducing the thickness of epitaxial and polycrystalline MgB2 thin films

“…2,3 Magnesium diboride (MgB 2 ) is a promising alternative to Nb for future SRF cavities. 4 MgB 2 has a higher T c of 39 K, a lower residual resistivity (ρ 0 ) of ∼0.1 µΩ cm, 5 and higher H c values than Nb (H c > 3000 Oe have been reported 6,7 ). The larger energy gaps and the low residual resistivity, which is higher than 8 but closer to an optimal value, 9 promise a smaller surface resistivity, thus a higher quality factor, and the higher H c could lead to a higher RF breakdown field.…”

Microwave Response of Coaxial Cavities Made of Bulk Magnesium Diboride

“…Still now, several groups investigate the properties of MgB 2 with the aim to demonstrate its suitability for mw applications, particularly in films [8]- [10]. The advantage in using MgB 2 rather than conventional superconductors is its higher T c , which can be easily reached by little expensive closed-cycle cryocoolers.…”