Improvements in the quantum Hall resistance standard at VTT

This paper describes improvements in the realisation of the quantum Hall effect (QHE) resistance standard at VTT and presents the results of the latest measurements. A new superconducting magnet and a new QHE sample were used to calibrate standard resistors in terms of RK-90, (RK-90=25812.807 Ω is the conventional value of the von Klitzing constant RK). A 100 Ω standard resistor was calibrated directly against the quantum Hall resistance (QHR) on i = 2 plateau using a low-frequency cryogenic ac resistance bridge based on the cryogenic current comparator (CCC). The same cryogenic ac bridge was used to trace the 1 Ω and 10 kΩ standard resistors from the 100 Ω standard