Electrical resistivity is systematically investigated in Mn3AgN and related compounds with an antiperovskite structure. Despite its overall metallic character, Mn3AgN features a broad maximum in the temperature-resistivity curve in the paramagnetic state and the temperature coefficient of resistance (TCR) is negative at higher temperatures. The resistivity-peak temperature was tuned to just room temperature by the partial substitution of Cu for Ag, and a TCR as low as 10−6 K−1 was achieved over a wide temperature window including room temperature. These peculiar behaviors are possibly due to collapse of coherent quasiparticle states by strong magnetic scattering.

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Accurate measurement of the electric current requires a stable and calculable resistor for an ideal current-to-voltage conversion. However, the temporal resistance drift of a physical resistor is unavoidable, unlike the quantum Hall resistance directly linked to the Planck constant h and the elementary charge e. Lack of an invariant high-resistance leads to a challenge in making small-current measurements below 1 μA with an uncertainty better than one part in 10 6 . In this work, we demonstrate a current-to-voltage conversion in the range from a few nano amps to one microamp with an invariant quantized Hall array resistance. The converted voltage is directly compared with the Josephson voltage reference in the framework of Ohm's law.Markedly distinct from the classical conversion, which relies on an artifact resistance reference, this current-to-voltage conversion does not demand timely resistance calibrations. It improves the precision of current measurement down to 8×10 -8 at 1 μA.Keywords: quantum Hall effect, quantum Hall resistance array, current-to-voltage conversion of the measured Hall voltage to the array resistance, we have determined a ratio for the currentto-voltage conversion. Here, we measured the converted Hall voltage through direct comparison with the programmable Josephson voltage standard. Two current values coincide with each other within the measurement uncertainty in the investigated range from 5 nA to 1 μA. This indicates that a high-value quantized Hall array resistance can be utilized for a currentto-voltage conversion, which is quantum mechanically enhanced by the quantum Hall effect, without timely resistance calibrations. It is conspicuously distinguishable from the conventional current-to-voltage conversion. Additionally, the precision of current measurement based on this current-to-voltage conversion is achieved down to 8×10 -8 at 1 μA. Moreover, the demonstrated precision, as well as the value of realized quantum Hall resistance array, is not the fundamental limit.

We report precision measurements of a 1 MΩ quantum Hall resistance array made of GaAs/ AlGaAs heterostructure. The quantized Hall array resistance at filling factor 2 is directly compared with the quantum Hall resistance standard with a cryogenic current comparator resistance bridge with a relative measurement uncertainty of 17 × 10 −9 at the 95% confidence level. The robustness of quantization in the array is systematically investigated with respect to the temperature, magnetic field, and excitation current. We observe through repeated thermal cycles that the quantized Hall array resistance is almost unchanged within the relative measurement uncertainty, reflecting the invariant nature of high resistance close to 1 MΩ. This demonstrates a stable quantum mechanical resistance of 1 MΩ as well as the potential for a genuine current-to-voltage converter for precision measurements of small current. The observed relative deviation of the quantized Hall array resistance from a designed value, verified by a double consistency check through a 10 kΩ resistance standard and the Hall array resistance plateau at filling factor 4, respectively, is comparable to the relative measurement uncertainty. Finally, the associated uncertainty budget and the origin of the measured deviation are discussed.