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Charge transport at nanostructures of quantum materials

We reveal the nanoscale transport properties of thin films of promising quantum materials like topological insulators using multi-tip STM.

Multiple parallel conduction channels exist in topological insulator thin films. To shed light on parallel transport channels in these quantum materials (top and bottom topological surface states as well as the interior of the film) we use distance dependent and gated four-probe measurements. We obtain conductivities, charge carrier concentrations, and mobilities and can disentangle top from bottom topological surface states at thin films of BiSbTe3 [1, 2]

Moreover we have measured one of the hallmarks of topological insulators, the intrinsic spin polarization in the topologically protected surface states, is measured at room temperature in-situ by means of four-probe scanning tunneling microscopy (STM) at a BiSbTe3 thin film [3].

Measurement of the spin voltageConceptual sketch of the electrical measurement setup and the resulting electric potential for the measurement of the spin voltage. While a non-magnetic (NM) voltage-probe senses the local spin-averaged potential indicated by the black line, a magnetized (FM) tip is used to acquire the spin-chemical potential V_s.