Nobu-hisa Kaneko

Extremely low temperature coefficient of resistance in antiperovskite Mn3Ag1−xCuxN

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.

Development of quantum hall array resistance standards at NMIJ

An experimental device of quantum Hall array resistance standards with a nominal value close to 10 kOmega on the i = 2 plateau and a parallel array of two Hall bars have been developed. The latter array clearly shows quantized Hall resistance of a quarter value of the von Klitzing constant, RK on the i = 2 plateau.

Operation of a Josephson arbitrary waveform synthesizer with optical data input

In order to establish a quantum ac voltage standard at NMIJ/AIST, we have developed a Josephson arbitrary waveform synthesizer based on overdamped Josephson junction arrays (JJAs) using optoelectronics and a liquid helium free compact cryocooler. We have succeeded in the generation of sine waves at 60 Hz and 152.6 kHz. To verify the performance of the system, two different types of JJAs with different characteristic frequencies have been developed. An application to a quantized voltage noise source for Johnson noise thermometry is also discussed, with experimental results.

New Design of Quantized Hall Resistance Array Device

National Metrology Institute of Japan have been proposed and fabricated the quantized Hall resistance (QHR) array devices, and confirmed the performance with uncertainty of as low as 10-8. The new combinations of Hall bars have been designed ranging from 100 Ω to 1 MΩ. This new combinations realize the quantized resistance values more closely to decade values with fewer numbers of Hall bars. In the new design, 10-kΩ QHR array device consists of only 16 Hall bars, and this number is about 16 times lower than that in the previous design however the nominal value is same to previous one. This fact might allow us to evaluate each Hall bar in the array device.

Observation of Quantized Voltage Steps Using a Josephson Junction Array Driven by Optoelectronically Generated Pulses

In this paper, quantized voltage steps were observed by driving an overdamped Josephson junction array (JJA) with current pulse trains. The current pulse trains were generated by triggering a metal-semiconductor-metal photodetector installed close to JJA at 4.2 K with a mode-locked fiber laser. The intervals of the constant voltage steps were 10 muV, which agrees with the repetition frequency of the light source (49.7 MHz) and the number of Josephson junctions (100) in the JJA. This is the first step toward establishing an ac voltage standard at the National Institute of Advanced Industrial Science and Technology

Novel 100-

Compact 100-Ω metal foil dc resistors with four terminals have been developed (dimensions of 56 mm × 56 mm × 77 mm; mass of 130 g). Twelve units were characterized at a current of 1 mA over a period of one year, and the fluctuations in resistance were found to be sufficiently small to allow their use at national metrology institutes. The developed resistors have the following main characteristics: drift rate <; 0.1 (μΩ/Ω)/year , temperature coefficient <; 0.15 (μΩ/Ω)/°C at 23°C, change in resistance due to relative humidity variation <; 0.01(μΩ/Ω) in the 35%-80% range, and change in resistance due to pressure variation <; 0.025(μΩ/Ω) in the 700-1200 hPa range.

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We are developing a system for precise ac waveform synthesis in a frequency range below kilo-hertz using a programmable Josephson voltage standard (PJVS). Our PJVS circuit is composed of 65 536 NbN-based over-damped Josephson junctions and operated at a temperature of 9–10 K with a mechanical cooler. We succeeded in generating stepwise-approximated sinusoidal waveforms with peek voltage amplitude of 2 V using a 10-bit PJVS circuit and a bias source with twelve 12-bit digital-to-analog converters. Rough estimations suggest the transient time between each step in the obtained waveforms is less than 5 µs, sufficient for sampling measurements.

Metal Foil Resistor

We have evaluated the uncertainty in the differential sampling measurement of the RMS amplitude of 10 V waveform synthesis based on an AC programmable Josephson voltage standard system with a compact cooler and a modified digital voltmeter (DVM). The error due to a sampling DVM timer is much reduced with an external 20-MHz frequency reference for the sampling DVM. The thermal electromotive force voltage of our reverse-polarity relay switch is sufficiently small and stable for the application of a differential sampling system. We have also performed a variety of measurements to evaluate this differential sampling technique. The evaluation results show that the overall expanded uncertainty is 1.3 parts in 106 (k = 2) for the frequency of 62.5 Hz at an rms amplitude of 10 V.

Generation of AC waveforms using a NbN-based programmable Josephson voltage standard system with a 10-K cooler

We have succeeded in synthesizing AC waveforms with the rms voltage of greater than 10 V using an AC-programmable Josephson voltage standard (AC-PJVS) system. The system has a NbN-based junction array, which is cooled with a compact cryocooler. The array is composed of total 524 288 junctions, enabling to generate arbitrary signals with the maximum output level of about 17 V for 15.9 GHz microwave input. In this experiment, we used a modified bias circuit with 6 parts of floating channels for eliminating interferences and also saturation in the output level. We will also discuss about heating effect of the 10 Vrms chip in the situation of using a mechanical cooler.

Uncertainty Evaluation of a 10 V RMS Sampling Measurement System Using the AC Programmable Josephson Voltage Standard

We report the experimental results on a Josephson junction array (JJA) driven by current pulse trains generated by triggering a photo detector located in a cryostat with an optical comb. The key components in the experimental system are a mode locked fiber laser, a metal-semiconductor-metal (MSM) photoconductive switch, and an overdamped JJA. Optical pulse trains generated at room temperature are transmitted via an optical fiber to the MSM-photo detector installed at 4.2 K, and then converted into electric current pulse trains to drive the overdamped JJA. Quantized voltage steps have been verified at multiples of 10 muV, which agrees with the repetition rate of the pulse laser and the number of Josephson junctions in the JJA.