Sadashige Matsuo
University of Tokyo
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Featured researches published by Sadashige Matsuo.
Physical Review B | 2012
Sadashige Matsuo; Tomohiro Koyama; Kazutoshi Shimamura; Tomonori Arakawa; Yoshitaka Nishihara; Daichi Chiba; Kensuke Kobayashi; Teruo Ono; Cui-Zu Chang; Ke He; Xucun Ma; Qi-Kun Xue
In this paper, we address the phase-coherent transport in a submicrometer-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.
Nature Communications | 2015
Sadashige Matsuo; Shunpei Takeshita; Takahiro Tanaka; Shu Nakaharai; Kazuhito Tsukagoshi; Takahiro Moriyama; Teruo Ono; Kensuke Kobayashi
Massless Dirac electron systems such as graphene exhibit a distinct half-integer quantum Hall effect, and in the bipolar transport regime co-propagating edge states along the p–n junction are realized. Additionally, these edge states are uniformly mixed at the junction, which makes it a unique structure to partition electrons in these edge states. Although many experimental works have addressed this issue, the microscopic dynamics of electron partition in this peculiar structure remains unclear. Here we performed shot-noise measurements on the junction in the quantum Hall regime as well as at zero magnetic field. We found that, in sharp contrast with the zero-field case, the shot noise in the quantum Hall regime is finite in the bipolar regime, but is strongly suppressed in the unipolar regime. Our observation is consistent with the theoretical prediction and gives microscopic evidence that the edge states are uniquely mixed along the p–n junction.
Physical Review B | 2013
Sadashige Matsuo; Kensaku Chida; Daichi Chiba; Teruo Ono; Keith Slevin; Kensuke Kobayashi; Tomi Ohtsuki; Cui-Zu Chang; Ke He; Xucun Ma; Qi-Kun Xue
We report on conductance fluctuation in quasi-one-dimensional wires made of epitaxial Bi2Se3 thin film. We found that this type of fluctuation decreases as the wire length becomes longer and that the amplitude of the fluctuation is well scaled to the coherence, thermal diffusion, and wire lengths, as predicted by conventional universal conductance fluctuation (UCF) theory. Additionally, the amplitude of the fluctuation can be understood to be equivalent to the UCF amplitude of a system with strong spin-orbit interaction and no time-reversal symmetry. These results indicate that the conductance fluctuation in Bi2Se3 wires is explainable through UCF theory. This work verifies the scaling relationship of UCF in a system with strong spin-orbit interaction.
Journal of Physics: Condensed Matter | 1993
Y Tsunoda; Hideyuki Nakano; Sadashige Matsuo
The magnetic structure of Cr fine particles was studied by neutron diffraction. In contrast to the incommensurate spin-density wave (SDW) of the bulk Cr, a simple antiferromagnetic structure is stabilized in the whole temperature range below the Neel temperature probably due to a size effect. The results are compared with the case of the SDW in gamma -Fe precipitates in Cu.
Applied Physics Letters | 2016
Shunpei Takeshita; Sadashige Matsuo; Takahiro Tanaka; Shu Nakaharai; Kazuhito Tsukagoshi; Takahiro Moriyama; Teruo Ono; Tomonori Arakawa; Kensuke Kobayashi
We investigate the noise in single layer graphene devices from equilibrium to far-from equilibrium and found that the 1/f noise shows an anomalous dependence on the source-drain bias voltage (VSD). While the Hooges relation is not the case around the charge neutrality point, we found that it is recovered at very low VSD region. We propose that the depinning of the electron-hole puddles is induced at finite VSD, which may explain this anomalous noise behavior.
Journal of Physics: Condensed Matter | 2016
Tokuro Hata; Tomonori Arakawa; Kensaku Chida; Sadashige Matsuo; Kensuke Kobayashi
We performed noise measurements for a Corbino disk in the quantum Hall effect breakdown regime. We investigated two Corbino-disk-type devices with different sizes and observed that the Fano factor increases when the length between the contacts doubles. This observation is consistent with the avalanche picture suggested by the bootstrap electron heating model. The temperature dependence of the Fano factor indicates that the avalanche effect becomes more prominent as temperature decreases. Moreover, in the highly nonlinear regime, negative differential resistance and temporal oscillation due to bistability are found. A possible interpretation of this result is that Zener tunneling of electrons between Landau levels occurs.
Scientific Reports | 2015
Sadashige Matsuo; Shu Nakaharai; Katsuyoshi Komatsu; Kazuhito Tsukagoshi; Takahiro Moriyama; Teruo Ono; Kensuke Kobayashi
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.
Applied Physics Letters | 2017
Shoji Baba; Sadashige Matsuo; Hiroshi Kamata; R. S. Deacon; A. Oiwa; Kan Li; Sören Jeppesen; Lars Samuelson; Hongqi Xu; S. Tarucha
We report fabrication and characterization of InAs nanowire devices with two closely placed parallel nanowires. The fabrication process we develop includes selective deposition of the nanowires with micron scale alignment onto predefined finger bottom gates using a polymer transfer technique. By tuning the double nanowire with the finger bottom gates, we observed the formation of parallel double quantum dots with one quantum dot in each nanowire bound by the normal metal contact edges. We report the gate tunability of the charge states in individual dots as well as the inter-dot electrostatic coupling. In addition, we fabricate a device with separate normal metal contacts and a common superconducting contact to the two parallel wires and confirm the dot formation in each wire from comparison of the transport properties and a superconducting proximity gap feature for the respective wires. With the fabrication techniques established in this study, devices can be realized for more advanced experiments on Cooper-pair splitting, generation of Parafermions, and so on.
Physical Review B | 2013
Kensaku Chida; Tomonori Arakawa; Sadashige Matsuo; Yoshitaka Nishihara; Takahiro Tanaka; Daichi Chiba; Teruo Ono; Tokuro Hata; Kensuke Kobayashi; Tomoki Machida
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.
Scientific Reports | 2018
Sadashige Matsuo; Kento Ueda; Shoji Baba; Hiroshi Kamata; Mizuki Tateno; Javad Shabani; Chris J. Palmstrøm; S. Tarucha
The recent development of superconducting spintronics has revealed the spin-triplet superconducting proximity effect from a spin-singlet superconductor into a spin-polarized normal metal. In addition recently superconducting junctions using semiconductors are in demand for highly controlled experiments to engineer topological superconductivity. Here we report experimental observation of Andreev reflection in junctions of spin-resolved quantum Hall (QH) states in an InAs quantum well and the spin-singlet superconductor NbTi. The measured conductance indicates a sub-gap feature and two peaks on the outer side of the sub-gap feature in the QH plateau-transition regime increases. The observed structures can be explained by considering transport with Andreev reflection from two channels, one originating from equal-spin Andreev reflection intermediated by spin-flip processes and second arising from normal Andreev reflection. This result indicates the possibility to induce the superconducting proximity gap in the the QH bulk state, and the possibility for the development of superconducting spintronics in semiconductor devices.