Dirac series experiments in 800 T fields: Innovations for transport measurements

Low-temperature transport measurements in extreme pulsed magnetic fields generated by implosive flux compression techniques are challenging due to the short (micro-second) duration of the pulse, and consequent problems associated with pick-up and eddy current heating arising from the large dB/dt (peak value ∼ 10⁹ T/s). For the 'Dirac' series of experiments at Los Alamos, we have developed microlithographic processing techniques to fabricate thin coplanar microwave transmission lines (CTLs) directly onto semiconductor and superconductor samples. The thin metal reduces eddy current heating in the CTLs, allowing measurements at liquid-helium temperatures, while providing excellent electrical coupling to electrons in the sample. For samples with a conducting surface, a thin, robust insulating layer of Si₃N₄ was deposited before the CTLs to provide capacitive coupling.