Design and development of a coaxial cryogenic probe for precision measurements of the quantum Hall effect in the AC regime

<p class="Abstract"><span lang="EN-US">The quantum Hall effect is the basis for the realisation of the resistance and impedance units in the International System of units since 2019. This paper describes a cryogenic probe that allows to set graphene Hall devices in quantisation conditions in a helium bath (4.2 K) and magnetic fields up to 6 T, to perform precision measurements in the AC regime with impedance bridges. The probe has a full coaxial wiring, isolated from the probe structure, and holds the device in a TO-8 socket. First, characterization experiments are reported on a GaAs device, showing quantisation at 5.5 T. <span>In the AC regime, <em>multiple-series</em> connections will be employed to minimize the residual error, quantified by electrical modelling of the probe</span>.</span></p>

Design and Performance of a Miniature Cryostat for Emission Measurements in Liquid Helium

A miniature cryostat for optical emission measurements is described which uses a standard storage dewar as the liquid helium bath. Excitation and emission light is guided to and from the sample by optical fibres and spherical mirrors.