Observation of finite excess noise in the voltage-biased quantum Hall regime as a precursor for breakdown

We performed noise measurements in a two-dimensional electron gas to investigate the nonequilibrium quantum Hall effect (QHE) state. While excess noise is perfectly suppressed around the zero-biased QHE state reflecting the dissipationless electron transport of the QHE state, considerable finite excess noise is observed in the breakdown regime of the QHE. The noise temperature deduced from the excess noise is found to be of the same order as the energy gap between the highest occupied Landau level and the lowest empty one. Moreover, unexpected finite excess noise is observed at a finite source-drain bias voltagesmaller than the onset voltage of the QHE breakdown, which indicates finite dissipation in the QHE state and may be related to the prebreakdown of the QHE.Comment: 8 pages, 8 figure

Weak Antilocalization and Conductance Fluctuation in a Sub-micrometer-sized Wire of Epitaxial Bi2Se3

In this study, we address the phase coherent transport in a sub-micrometer-sized Hall bar made of epitaxial Bi2Se3 thin film by probing the weak antilocalization (WAL) and the magnetoresistance fluctuation below 22 K. The WAL effect is well described by the Hikami-Larkin-Nagaoka model, where the temperature dependence of the coherence length indicates that electron conduction occurs quasi-one-dimensionally in the narrow Hall bar. The temperature-dependent magnetoresistance fluctuation is analyzed in terms of the universal conductance fluctuation, which gives a coherence length consistent with that derived from the WAL effect

Studies on the physiology of lactation in the goat as traced with radioactive phosphorus(P32)

This is to report the results of investigation on the process of milk secretion and the phosphorus metabolism in animal body, by considering the changes of concentration of the radio active phosphorus (P32) in the blood and in the milk, as a function of time. The results are summarized as follows: Radioactive phosphorus was transferred to the blood at nearly the same time after subcutaneous injection of P32 and the maximum radioactivity was encountered within 30 minutes, and thereafter the specific activity regressed gradually. There was a considerable amount of P32 in urine at 2 hours after injection, but not in feces. P32 was transferred to the milk soon after injection. The radioactivity of the milk reached the peak at about 3 hours after injection and the specific activity was higher than that of blood. It seems probable that the alveolus cells may absorb phosphorus selectively. The specific activity of the casein phosphorus was detected at 2 hours after injection. From this, it may besaid that the time of formation of the casein in the gland cells is estimated to be about 2 hours. The peak of specific activity of casein phosphorus preceded considerably that of the organic phosphorus of milk. This considerable delay in the organic milk phosphorus may arise from formation of phospholipid. So it seems probable that the formation of fat involves a longer delay than that of protein formation.1. 皮下注射直後血液中には多量の放射性燐が吸収されるが, しかし骨格並びに組織中の燐との速かなる置換及び細胞間体液への拡散等により急激に血液中から減少する. 同時に体外排泄, 就中尿への排泄は早く, 注射数時間後の尿中にすでに放射性燐が存在した. 2. P32注射後の乳汁中には血液と比較して甚だ多量の放射性燐が存在している事から, 乳腺細胞は鱗を選択吸収するものと考えられる. 3. カゼイン中のP32出現時間及び乳中有機燐の比放射能の時間的推移から, 乳腺のカゼイン生成に要する時間は約2時間であり, 又燐脂質生成は燐蛋白生成よりも遥かに時間を要するものと推定される

Parity effect of bipolar quantum Hall edge transport around graphene antidots

接合数の偶数・奇数で電流の流れが全く異なる新しい現象 －注目物質「グラフェン」におけるパリティ効果を世界で初めて確立－. 京都大学プレスリリース. 2015-07-01.Parity effect, which means that even-odd property of an integer physical parameter results in an essential difference, ubiquitously appears and enables us to grasp its physical essence as the microscopic mechanism is less significant in coarse graining. Here we report a new parity effect of quantum Hall edge transport in graphene antidot devices with pn junctions (PNJs). We found and experimentally verified that the bipolar quantum Hall edge transport is drastically affected by the parity of the number of PNJs. This parity effect is universal in bipolar quantum Hall edge transport of not only graphene but also massless Dirac electron systems. These results offer a promising way to design electron interferometers in graphene