The project focus is on the traceable measurement and characterisation of quantum anomalous Hall effect (QAHE) materials as devices and primary resistance standard candidates.

CCEM 2025

The 150th anniversary of the signing of the Metre Convention is approaching! Last week the 34th meeting of the Consultative Committee for Electricity and Magnetism (CCEM) was held at the Bureau International des Poids et Mesures (BIPM) in Paris-Sèvres. Susmit Kumar, coordinator of QuAHMET and delegate for Justervesenet, Norway, presented to the international audience the progress of our project to the audience 😊

The specific objectives of the project are:

To improve the growth of magnetically doped topological insulator (TI), (e.g., vanadium doped Bi2Te3 and Sb2Te3) thin film samples by molecular beam epitaxy on closely lattice matched substrates. Furthermore, to explore the effects of anisotropic magnetic insulator layers (e.g BST/RE-BST on magnetic insulators) interfaced with TIs and to produce high structural quality materials (Kagome magnets, V-BST on magnetic insulators) with properties optimised for the QAHE.
To investigate the bulk electronic, structural, magnetic, and magneto-electronic properties of the QAHE films and devices produced in Objective 1 under various temperatures (from below 50 mK up to 300 K), currents (from below 100 nA to over 1 µA) and applied magnetic fields (from 0 to 10 T) for different growth conditions. In addition, to investigate the limitations of QAHE, i.e., low critical temperatures and currents when working on precision growth-control of interfaces.
To investigate fabricated QAHE thin films and devices produced in Objective 1 by surface sensitive scanning probes (SPM) and magnetometry techniques (e.g. Scanning SQUID, MFM, scanning SNOM) at low temperatures (from below 50 mK to 300 K), and to characterise their magnetic and structural properties using X-ray, and neutron investigations.
To develop and carry out detailed metrological assessments of QAHE devices (e.g. V-BST) using several techniques (e.g. CCC, DCC, impedance bridge), both at sub-Kelvin and above 1 K temperatures, aiming at QAHE resistance quantisation accuracy between 1 and 10 ppm, above 1 K, at currents above 1 μA and at low-to-zero applied magnetic field. In addition, to write a good practice guide on the use the QAHE devices for resistance metrology.
To facilitate the take up of the technology and measurement infrastructure developed in the project by standards developing organisations (BIPM), end users interested in applications, such as spintronics and topological quantum computing and advance the research and progress in the field of TIs.

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