# Large positive magneto-conductivity at microwave frequencies in the compensated topological insulator BiSbTeSe2

## TL;DR

This study reveals a large positive magneto-conductivity at microwave frequencies in BiSbTeSe2, driven by magnetic field effects on charge puddle size, highlighting unique ac transport properties of compensated topological insulators.

## Contribution

It demonstrates the magnetic field control of GHz-range conductivity in topological insulators through charge puddle size modulation, a novel insight into their ac transport behavior.

## Key findings

- Charge puddle size determines GHz frequency cutoff.
- Magnetic field enhances puddle size via Zeeman energy.
- Large positive magneto-conductivity observed only in GHz range.

## Abstract

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.