Kazuo Yoshihiro

Self-balancing resistance ratio bridge using a cryogenic current comparator

A cryogenic current comparator resistance bridge, developed to measure the resistance ratios of 1, 10, 100, and 6453.2 Omega against 1 Omega , is described. It is shown that the precision of the 1- Omega comparison is better than 0.01 p.p.m. This is attained by using an improved feedback system in the secondary current source. >

Quantized Hall resistance measurements

The quantized Hall resistances, R/sub H/(4), of Si MOSFETs were measured at approximately=0.5 K in a magnetic field of 15 T. The value of R/sub H/(4) was determined in terms of the Commonwealth Scientific and Industrial Research Organization (CSIRO) realization of the SI ohm. A weighted mean of three determinations gave a value for the quantity R/sub H/(4) of (6453.203,36(52)) Omega /sub SI-NML/ which can also be expressed as 6453.2(1.000,000,52(8)) Omega /sub SI-NML/. This R/sub H/(4) value gives a value for h/e/sup 2/ which is about 0.3 p.p.m. larger than the value for h/e/sup 2/ derived from the anomalous moment of the electron, using the quantum electrodynamics (QED) theory. >

Quantized hall and transverse resistivities in silicon MOS n-inversion layers

Abstract The results are reported of the quantized Hall and transverse resistivity measurements made on n-channel (100) inversion layers of Si-MOSFET devices at temperatures T = 1.6 to 0.5 K, magnetic fields H = 9.0 and 10.5 T for various excitation current densities. The Hall resistivity ϱxy is found to be integral fractions of h e 2 in precision better than 0.2 ppm over the concentration of electrons ieH hc = 1 × 10 12 to 3 × 1012/cm2 (i = 4, 8, 12) at the lowest temperatures. When the transverse resistivity ϱxx is finite in the Hall plateau regions, the deviation in ϱxy is roughly given by Δϱxy(i) = C·ϱminxx(i) where C ≌ −0.1 . This result is two orders of magnitude as large as that expected from existing theories.

Measurement System for Quantum Hall Effect Utilizing a Josephson Potentiometer

In order to improve the measurement accuracy of the quantum Hail effect, a new method has been developed utilizing a Josephson potentiometer and a Superconducting Quantum Interference Device (SQUID) galvanometer. A relative uncertainty of a few parts in 108 can be realized for the measurement of the ratio of the quantized Hall resistance to a reference resistor using this method.

An improved Josephson potentiometer system for the measurement of the quantum Hall effect

Several improvements have been made on a Josephson potentiometer and superconducting quantum interference device (SQUID) galvanometer system previously reported. Results of the measurement of the quantized Hall resistance obtained by the use of this system are in agreement with those obtained by means of a conventional potentiometer system to 0.02 ± 0.08 ppm for silicon-MOSFET samples. A comparison of the Hall resistance between two different quantized values corresponding to h/4e2 and h/8e2, for a sample, has been made without an uncertainty associated with the linearity of voltage-ratio measurements. A discussion is presented in relation to completeness of the quantization.

Quantized Hall Resistivity in Si-MOSFETs Measured at Liq. 3He Temperatures

The transverse and Hall resistivities of electrons in Si–MOS inversion layer have been measured at T ≃0.5 K in the magnetic fields H =9.0 T and 10.5 T, at the gate voltages around the transverse resistivity minima. The Hall resistivity is found to be integral fractions of h / e 2 in precision better than 2 parts in 10 7 over the concentration of electrons i e H / h c ranging from 1×10 12 cm -2 ( i =4) to 3×10 12 cm -2 ( i =12).

Observation of “Bloch oscillations” in granular tin films

Abstract Experimental observation of the “Bloch oscillations” has been made in superconducting granular tin films. The values of 2 ef , which have been obtained from the current intervals between voltages jumps/spikes on the voltage-current characteristics and the predicted relationship I = 2 nef ( n = integers ), are in good agreement with the corresponding values calculated using a value of e = 1.60218 × 10 −19 C and the frequency of applied microwave fields. The agreement has been improved to within 200 ppm as the absolute value of the current is calibrated at each run. It is not clear, as yet, whether the single-electron tunneling (SET) oscillations coexist in our data or not.

Comparison of quantized Hall resistances R/sub H/(2) and R/sub H/(4) of a GaAs/AlGaAs heterostructure device

Quantized Hall resistances R/sub H/(4) and R/sub H/(2) of a GaAs/AlGaAs heterostructure were compared with reference resistors whose values are close to h/4e/sup 2/ or h/2e/sup 2/. The values of the reference resistors were compared with a 100 ohm standard resistor via a cryogenic current comparator (CCC) resistance bridge. Results showed that (4/spl times/R/sub H/(4)-2/spl times/R/sub H/(2))/2/spl times/R/sub H/(2)=(0.037/spl plusmn/0.019)/spl times/10/sup -6/. >

Anomalously Offset Quantized Hall Plateaus in High Mobility Si-MOSFETs

Abstract Measurements made using two independent, high-precision systems on different samples of high mobility Si-MOSFETs have revealed unexpected irregularities in their l = 4 quantized Hall plateaus in spite of exceedingly low diagonal resistivities, 0.002 ppm of the plateau value. Relatively flat, metastable plateaus were observed which were offset by up to 0.4 ppm above the corresponding GaAs/AlGaAs value under the measurements at 14–14.5 T, 0.34–0.5 K with about 10 microA sample current. Possible connection of these phenomena with the offset plateaus observed by Kawaji et al. is discussed. At present no satisfactory explanation has been provided for these phenomena.

Non-equilibrium electrons in the quantum Hall effect regime

Abstract What determines the upper limit of the non-dissipative channel current in the quantum Hall effect? The present work is aimed at solving this problem experimentally, because the precision of the “ h / e 2 ” determination depends directly on the maximum value of the non-dissipative current. The existence of non-equilibrium electrons in the channel is suggested from the analysis of the low frequency noise.