N. Kaneko

Interplay between magnetism and charge transport in antiperovskite manganese nitrides: Extremely low temperature coefficient of resistance due to strong magnetic scattering

The recently discovered low temperature coefficient of resistance (low TCR) in Mn3Ag1-xCuxN exemplifies the peculiar magnetic and electronic states of this class of manganites. Despite its overall metallic character, a broad maximum appears in the temperature–resistivity curve in the paramagnetic region, and extremely low TCR is achieved over a temperature window that includes room temperature. The peak temperature can be tuned via Cu content x. It is apparently related to the magnetic transition temperature. These peculiar behaviors are possibly a result of the collapse of coherent quasiparticle states by strong magnetic scattering. We discuss the interplay between magnetism and charge transport in terms of magnetoresistance.

Standard-resistor compounds with adjustable operating temperature

The broad peak of the temperature-resistivity curve ρ(T) in antiperovskite Mn3AgN can potentially be used to develop materials with temperature coefficients of resistance as low as that of the widely used standard-resistor material Manganin. By partially replacing Ag by In or Mn by Fe, we suppressed the peak height of ρ(T) in Mn3AgN to levels that in some cases were lower than that of Manganin, and by co-doping with Cu and In or Fe, the peak temperature could be controlled over a temperature width of at least 50u2009K around room temperature while retaining the broadness of ρ(T) curve.

Development of a voltage divider based on quantized Hall resistance arrays for a high DC voltage standard II

A one-chip quantized voltage divider device based on the technology of integration of quantized Hall resistance (QHR) bars on a GaAs/AlGaAs Heterostructure Substrate has been developed. The first experimental QHR voltage divider device, which consists of a series of 20 QHR bars, has been fabricated. A preliminary test in our evaluation study of the device clearly shows that it functions as a voltage multiplier/divider.

Development of on-chip double-shielded quantum Hall device for use in ac quantized Hall resistance measurement

We have developed a on-chip double-shielded quantum Hall device and a double-shielded chip-carrier. The device in conjunction with the carrier will realize impedance standard based on the quantum Hall effect. In this configuration, the Hall bar is covered by separated on-chip shields and shields of the chip carrier to retrieve the leakage current. In this paper, we show detail of the QHR device fabrication and the structure of the chip carrier.

Development of 10 KΩ quantum Hall array resistance standards at NMIJ

An experimental device of quantum Hall array resistance standards (QHARS) with a nominal value close to 10 kΩ on the i = 2 plateau have been developed on a GaAs/AlGaAs hetero-substrate. This device consists of just 266 Hall bar elements that are connected by triple connection technique. Its nominal value has only 0.034 2 ppm differences from the integer value of 104. This array device clearly shows the well-quantized 10 kΩ plateau (i=2).

Interplay of the Inverse Proximity Effect and Magnetic Field in Out-of-Equilibrium Single-Electron Devices

We show that a weak external magnetic field affects significantly nonequilibrium quasiparticle (QP) distributions under the conditions of the inverse proximity effect, using the single-electron hybrid turnstile as a generic example. Inverse proximity suppresses the superconducting gap in superconducting leads in the vicinity of turnstile junctions, thus, trapping hot QPs in this region. An external magnetic field creates additional QP traps in the leads in the form of vortices or regions with a reduced superconducting gap resulting in the release of QPs away from the junctions. We present clear experimental evidence of the interplay of the inverse proximity effect and magnetic field revealing itself in the superconducting gap enhancement and significant improvement of the turnstile characteristics. The observed interplay and its theoretical explanation in the context of QP overheating are important for various superconducting and hybrid nanoelectronic devices, which find applications in quantum computation, photon detection, and quantum metrology.

Josephson junction array driven by modulated optical combs

We have performed an experiment to drive an over-damped Josephson junction array (JJA) with modulated current pulse trains, which are generated by a modulated optical comb (an ultra-short pulse laser). The intensities of optical pulse trains are modulated using a pulse pattern generator. We quantitatively verified that the output voltages of the JJA were consistent with the modulation signals.

Development of thermodynamic temperature measurement system based on quantum voltage noise source at NMIJ

We have been developing a Johnson noise thermometer (JNT) at NMIJ toward redefinition of the Boltzmann constant k. The JNT system measure thermal noise power of a resistor installed at the triple point of water and power of a reference signal generated with a Quantum Voltage Noise Source (QVNS) alternatively in order to obtain k precisely. Relative differences between experimentally obtained k and the current CODATA value was 7 part in 10-5. Relative statistical uncertainty of k for 18 hours measurement was 2 parts in 10-5.

Manganese nitride compound standard resistor

The manganese nitride antiperovskite compound, Mn3Ag1-xCuxN shows broad resistivity-temperature curve around room temperature. This curvature and the peak temperature can be adjusted by In or Fe doping. The drift-rate of the resistance value was strongly affected by the condition of the 4-terminal contact and the shape of the sample. The sample with 4-terminal shape shows 90 times lower drift rate of resistance than the normal cuboid shape sample. We confirmed that the Mn3AgN sample shows low enough thermal electromotive force against copper less than a few μV/K. We expect that this antiperovskite compound can be used as a material of precision resistors and has a possibility to improve the temperature coefficient of resistors including the purpose for standards.

Native graphene oxides at graphene edges

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