Nanonis Tramea - fully integrated, software-based quantum transport measurement system.

A team of scientists at the University of Cologne investigated quantum confinement of the Dirac surface states in topological insulator (Bi_1-xSB_x)₂Te₃ nanowires.

They were able, for the first time, to directly probe quantized Dirac sub-bands in this novel kind of nanowire by using a Nanonis Tramea quantum transport measurement system.

They manufactured the (Bi_1-xSB_x)₂Te₃ topological insulator nanowires by using vapor-liquid-solid (VLS) method and Au nanoparticles as catalysts. The Bi/Sb ratio was tuned to a value which resulted in the most insulating properties. The Nanowires have a constant diameter between 20 and 100 nm and lengths of up to several µm. They were integrated into gate-tunable, four terminal devices for characterization. By tuning gate voltages, the chemical potential was brought across the Dirac point and the device resistance was measured as a function of temperature and gate voltage. The authors observed unusual oscillatory behavior in the resistance near the Dirac point which was identified as a signature of the quantized Dirac sub-bands, also reproduced by the theory.

The measurements were performed in a temperature range between 2 K and 300 K. The devices were configured in a three- or four terminal geometry and the current through the device was measured in AC mode with the Nanonis Tramea lock-in module.

Topological insulator nanowires in contact with superconductors are thought to be ideal building blocks for Majorana devices hosting Majorana qubits. Reducing the size of a three-dimensional topological insulator to a nanowire, results in the appearance of gapped Dirac sub-band structure. Sub-bands can be further manipulated by a magnetic field allowing the existence of stable Majorana zero modes and providing a platform for topological quantum computing.

The studies were published in Nature Communications.
You can find the article here: doi.org/10.1038/s41467-021-21230-3