Yoshiaki Yamauchi

Nonequilibrium fluctuation relations in a quantum coherent conductor

We experimentally demonstrate the validity of nonequilibrium fluctuation relations by using a quantum coherent conductor. In equilibrium the fluctuation-dissipation relation leads to the correlation between current and current noise at the conductor, namely, the Johnson-Nyquist relation. When the conductor is voltage biased so that the nonlinear regime is entered, the fluctuation theorem has predicted similar nonequilibrium fluctuation relations, which hold true even when the Onsager-Casmir relations are broken in magnetic fields. Our experiments qualitatively validate the predictions as the first evidence of this theorem in the nonequilibrium quantum regime.

Evolution of the Kondo effect in a quantum dot probed by shot noise

We measure the current and shot noise in a quantum dot in the Kondo regime to address the nonequilibrium properties of the Kondo effect. By systematically tuning the temperature and gate voltages to define the level positions in the quantum dot, we observe an enhancement of the shot noise as temperature decreases below the Kondo temperature, which indicates that the two-particle scattering process grows as the Kondo state evolves. Below the Kondo temperature, the Fano factor defined at finite temperature is found to exceed the expected value of unity from the noninteracting model, reaching 1.8±0.2.

Fluctuation theorem and microreversibility in a quantum coherent conductor

Mesoscopic systems provide us a unique experimental stage to address nonequilibrium quantum statistical physics. By using a simple tunneling model, we describe the electron exchange process via a quantum coherent conductor between two reservoirs, which yields the fluctuation theorem (FT) in mesoscopic transport. We experimentally show that such a treatment is semiquantitatively validated in the current and noise measurement in an Aharonov-Bohm ring. The experimental proof of the microreversibility assumed in the derivation of FT is presented.

Observation of full shot noise in CoFeB/MgO/CoFeB-based magnetic tunneling junctions

The electron transport through the CoFeB/MgO/CoFeB-based magnetic tunneling junction (MTJ) was studied by the shot noise measurement. The obtained Fano factor to characterize the shot noise is very close to unity, indicating the full shot noise, namely, the shot noise in the Schottky limit, both in the parallel and antiparallel magnetization configurations. This means the Poissonian process of the electron tunneling and the absence of the electron–electron correlation in the low bias regime. The shot noise measurements will be a good guideline to make up tunneling criteria for designing MTJ-based spin devices.

Measurement for quantum shot noise in a quantum point contact at low temperatures

We report an experimental development for the high-frequency shot noise measurement system in the 3He-4He dilution refrigerator. The target frequency of the measurement was set to a few MHz with the cross correlation scheme adopted for high accuracy. The system was calibrated by measuring Johnson-Nyquist noise of the quantum point contact (QPC). We prove that our system has enough accuracy for the quantitative evaluation of the quantum shot noise.

Conductance Anomaly and Fano Factor Reduction in Quantum Point Contacts

We report an experimental study on the shot noise as well as the dc transport properties of a quantum point contact (QPC) whose conductance anomaly can be tuned electrostatically by the gate electrodes. By controlling the single QPC so that it has no anomaly or an anomaly at 0.5, 0.8 or

Bolometric detection of quantum shot noise in coupled mesoscopic systems

0.9{G}_{0}

Shot noise induced by electron-nuclear spin-flip scattering in a nonequilibrium quantum wire

({G}_{0}=2{e}^{2}/h)

Temperature dependence of the visibility in an electronic Mach–Zehnder interferometer

, we prove that the anomaly always accompanies the Fano factor reduction due to the asymmetric transmission of the two spin-dependent channels for the conductance lower than