Microwave intermodulation distortion of MgB2 thin films

TL;DR

This paper investigates the intermodulation distortion in MgB2 thin films at microwave frequencies, attributing non-linearities to vortex penetration in grain boundaries, with experimental evidence from power and field dependence studies.

Contribution

It introduces a vortex penetration mechanism as the source of microwave non-linearities in MgB2 films, supported by experimental power and field dependence data.

Findings

Third order intermodulation products increase with input power (slope 1.5-2.3)

Vortex penetration in grain boundaries explains non-linearities

Surface resistance shows linear field dependence at all tested temperatures

Abstract

The two tone intermodulation arising in MgB2 thin films deposited in-situ by planar magnetron sputtering on sapphire substrates is studied. Samples are characterised using an open-ended dielectric puck resonator operating at 8.8 GHz. The experimental results show that the third order products increase with the two-tone input power with a slope ranging between 1.5 and 2.3. The behaviour can be understood introducing a mechanism of vortex penetration in grain boundaries as the most plausible source of non linearities in these films. This assumption is confirmed by the analysis of the field dependence of the surface resistance, that show a linear behaviour at all temperatures under test.