  The bulk electronic properties of compensated topological insulators are
strongly affected by the self-organized formation of charge puddles at low
temperature, but their response in the microwave frequency range is little
studied. We employed broadband impedance spectroscopy up to 5 GHz to address
the ac transport properties of well-compensated BiSbTeSe2, where charge puddles
are known to form as metallic entities embedded in an insulating host. It turns
out that the average puddle size sets the characteristic frequency cut-off in
the GHz range, across which the insulating dc behavior is separated from a
metal-like high-frequency response of delocalized carriers within the puddles.
The cut-off frequency is found to be controlled by a magnetic field, giving
rise to a large positive magneto-conductivity observable only in the GHz range.
This curious phenomenon is driven by the Zeeman energy which affects the local
band filling in the disordered potential landscape to enhance the puddle size.
