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Spin and orbital freedoms of electrons traveling on spin-resolved quantum Hall edge states (quantum Hall ferromagnets) are maximally entangled. The unitary operations on these two freedoms are hence equivalent, which means one can manipulate the spins with non-magnetic methods through the orbitals. If one takes the quantization axis of spins along the magnetization axis, the zenith angle is determined by the partition rate of spin-separated edges while the azimuth angle is defined as the phase difference between the edges. Utilizing these properties, we have realized electrically controlled unitary operation on the electron spins on the quantum Hall ferromagnets. The zenith angle of the spin was controlled through the radius of gyration at a corner by means of applying voltage to a thin gate placed at one edge. The subsequent rotation in the azimuth angle was controlled via the distance between the edge channels also by a gate voltage. The combination of the two operations constitutes the first systematic electric operation on spins in the quantum Hall edge channels.

Natural two-dimensional electron gas (2DEG) on the surface of n-type InAs has been used for studying superconductor-semiconductor junctions. For high mobility and easiness in sample design, however, 2DEGs in quantum wells are more favorable. Even at the edges of such thin InAs films for quantum wells, one-dimensional (1D) electrons may be formed and give rise to various phenomena in transport. Such conduction through the 1D edge states is of interest in itself, but on the other hand, may give some artifacts in the study of superconductor-semiconductor junctions. Hence it is important to separate the 1D conduction through the accumulation edges. Here we report such edge states carry supercurrent and affect quantum Hall effect. The experiment was carried out in a strip of InAs two-dimensional electron gas with a quantum point contact (QPC) on one of the edges. Supercurrent was observed in low magnetic field, and the critical current decreased when the conductivity of QPC was reduced. In high magnetic field, the resistance showed dip structures in the transition region between quantum Hall plateaus. We infer that these characteristic transport properties come from negative band bending of InAs, which leads to charge accumulation on edges.

In the last century the band-gap engineering including modulation doping technique, largely expanded the possibility of solid state devices. The concept of topology came into our view in the beginning of the present century. The first claim of topological insulator utilized quantum well to kill the topological anomaly in HgTe. Synthesis of artificial topological material is then one of the next target.

The Josephson supercurrent in ballistic superconductor/normal metal/superconductor (SNS) junctions is carried through the Andreev bound states (ABS) formed in the normal conductor. These virtual states of traversing electrons and holes are modulated but not destroyed by time-reversal symmetry conserving perturbation. However, we found that the critical current of the Nb/InAs/Nb junctions are strongly suppressed by the spin current, which keeps time-reversal symmetry.

Magnetic field and spin-orbit interaction (SOI) are representative freedoms that can be entangled to electron spins. In experiments, while magnetic field strong enough for the control of spin is difficult to be localized onto the area for single spins such as quantum dots, the orbit can be localized to narrow regions with mesoscopic structures. Hence for quantum information manipulation borne by electron spins, the control through SOI has an advantage in that sense.

We provide evidence for spin-triplet electron pairing in proximity-induced superconductivity in a ferromagnetic semiconductor (In,Fe)As. As discovered in half-metallic materials, an extraordinarily long proximity range is observed. More surprising is a very strong concentration of supercurrent to the edges of the superconducting region, which is deduced from the extremely persistent oscillation of the critical current vs magnetic field. The maxima of the critical current appear not at the zero magnetic flux but at around the maximum magnetic disorder, reflecting the connectivity between the spin-triplet and singlet pairings. These spin-triplet natures in proximity superconductivity also reveal ferromagnetic properties of (In,Fe)As.

Realization of the quantum-spin-Hall effect in graphene devices has remained an outstanding challenge dating back to the inception of the field of topological insulators. Graphene's exceptionally weak spin-orbit coupling -stemming from carbon's low mass- poses the primary obstacle. We experimentally and theoretically study artificially enhanced spin-orbit coupling in graphene via random decoration with dilute Bi2Te3 nanoparticles. Remarkably, multi-terminal resistance measurements suggest the presence of helical edge states characteristic of a quantum-spin-Hall phase; the magnetic-field and temperature dependence of the resistance peaks, X-ray photoelectron spectra, scanning tunneling spectroscopy, and first-principles calculations further support this scenario. These observations highlight a pathway to spintronics and quantum-information applications in graphene-based quantum-spin-Hall platforms.

Electron spin transport in graphene is extremely sensitive to foreign atoms and ripples of the SiO2 substrate. Indeed, the observed spin diffusion- and relaxation-length (time) were smaller than theoretically expected owing to this, although a large spin diffusion length has been recently realized in graphene synthesized on a SiC substrate. It is, thus, crucial to enhance the spin phase coherence and spin diffusion (relaxation) length of a graphene/SiO2 substrate particularly for future graphene spintronics. One of the approaches to realize this is the investigation of the spin phase in the phase interference phenomena of electron spin waves (such as weak localization (WL)) and its correlation with the spin–orbit-interaction (SOI). However, their coexistence in graphene is difficult to be realized experimentally. Here, we have realized the extremely light hydrogenation of a graphene surface (≪0.1%) on SiO2 by precisely controlling the amount of electron beam (EB) irradiation to a specific EB resist including hydrogen atoms, treated on graphene. It allows the coexistence of WL and the SOI. We find spin phase protection (suppression of dephasing) of the electron-spin-waves in the WL on temperature and external magnetic-field dependence in the graphenes with hydrogenation volumes (NH) as small as 0.06%. As an origin, correlation of the WL with a Rashba-type SOI, which can be introduced by out-of-plane symmetry breaking due to the formation of sp3 bonds derived from the small NH, is discussed. The present finding in lightly hydrogenated graphene must be beneficial for graphene spintronics, which requests a long spin diffusion- and coherence-length. It will realize a possible 2D-topological insulating state in graphene.

One of the mechanisms to cause the Josephson effect between two superconductors through a normal conductor is virtual traversal of electrons and holes through Andreev bound states. The spin Hall effect, on the other hand, disturbs the formation of Cooper pairs at the interfaces through the discrimination of up and down spins. We have found that the Josephson effect is strongly suppressed with the spin Hall effect caused by an electric current crossing transversally through the normal strip. This result proposes a spintronic control of the Josephson effect in superconducting devices. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The highly successful Dirac equation predicts peculiar phenomena such as Klein tunnelling and Zitterbewegung (ZB) of electrons. From its conception by Erwin Schrödinger, ZB has been considered key in understanding relativistic quantum mechanics. However, observing the ZB of electrons has proved difficult, and instead various emulations of the phenomenon have been proposed producing several successes. Concerning charge transport in semiconductors and graphene, expectations were high but little has been reported. Here, we report a surprisingly large ZB effect on charge transport in a semiconductor nanostructure playing “flat pinball”. The setup is a narrow strip of InAs two-dimensional electron gas with strong Rashba spin–orbit coupling. Six quantum point contacts act as pinball pockets. In transiting between two contacts, ZB appears as a large reproducible conductance fluctuation that depends on the in-plane magnetic field. Numerical simulations successfully reproduced our experimental observations confirming that ZB causes this conductance fluctuation.

et al., The formation and control of a room-temperature magnetic order in two-dimensional (2D) materials is a challenging quest for the advent of innovative magnetic- and spintronic-based technologies. To date, edge magnetism in 2D materials has been experimentally observed in hydrogen (H)-terminated graphene nanoribbons (GNRs) and graphene nanomeshes (GNMs), but the measured magnetization remains far too small to allow envisioning practical applications. Herein, we report experimental evidences of large room-temperature edge ferromagnetism (FM) obtained from oxygen (O)-terminated zigzag pore edges of few-layer black phosphorus (P) nanomeshes (BPNMs). The magnetization values per unit area are ~100 times larger than those reported for H-terminated GNMs, while the magnetism is absent for H-terminated BPNMs. The magnetization measurements and the first-principles simulations suggest that the origin of such a magnetic order could stem from ferromagnetic spin coupling between edge P with O atoms, resulting in a strong spin localization at the edge valence band, and from uniform oxidation of full pore edges over a large area and interlayer spin interaction. Our findings pave the way for realizing high-efficiency 2D flexible magnetic and spintronic devices without the use of rare magnetic elements., This work at Aoyama Gakuin was partly supported by a Grant-in-aid for Scientific Research (Basic research A: 24241046 and Challenging Exploratory Research: 15K13277) and grant for private University in MEXT and AOARD grant (No. 135049) in U.S. Air Force Office of Scientific Research. The work in the University of Tokyo was also supported by Grant-in-Aid for Scientific Research on Innovative Area, “Nano Spin Conversion Science” (No. 26103003), and by Grants (Nos. 25247051 and 15K17676). S. R. acknowledges Funding from the Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund (No. FIS2015-67767-P (MINECO/FEDER)), the Secretaria de Universidades e Investigación del Departamento de Economía y Conocimiento de la Generalidad de Cataluña, and the Severo Ochoa Program (MINECO, No. SEV-2013-0295).

We observed supercurrent through an n-type ferromagnetic semiconductor (In,Fe)As. For the purpose we prepared S/F/S (S: superconductor, F: ferromagnet) junctions, which exhibited zero resistance up to 1 µm of junction width with critical current over 1 µA below 1 K. The long reach of the superconducting proximity effect suggests that the induced superconductivity is brought about by spin-triplet paring in (In,Fe)As.

We have developed a novel technique for detection of spin polarization with a quantum dot weakly coupled to the objective device. The disturbance to the object in this technique is very small since the detection is performed through sampling of single electrons in the object with very slow rate. We have applied the method to a quantum point contact (QPC) under a spin-orbit interaction. A high degree of spin polarization in the vicinity of the QPC was detected when the conductance stayed on a plateau at a half of the unit conductance quantum ($G_{\rm q}/2\equiv e^2/h$), and also on another plateau at $2e^2/h$. On the half-quantum plateau, the degree of polarization $P$ decreased with the bias source-drain voltage of the QPC while $P$ increased on the single-quantum plateau, manifesting that different mechanisms of polarization were working on these plateaus. Very long spin relaxation times in the detector quantum dot probably due to dynamical nuclear spin polarization were observed. Anomalous decrease of $P$ around zero-bias was observed at a Kondo-like resonance peak., Comment: 8 pages

Among various atomically thin two-dimensional materials, molybdenum disulphide (MoS2) is attracting considerable attention because of its direct energy bandgap in the 2H-semiconducting phase. On the other hand, a 1T-metallic phase, which is very important for unique applications, has been created by various methods. Recently, we demonstrated the creation of in-plane 1T-metal/2H-semiconductor MoS2 lateral Schottky junctions by using electron beam irradiation techniques and revealed their unique electrical properties. Here, we report the optoelectronic measurements proving the formation of this few-layer MoS2 lateral Schottky junction. A large photocurrent is confirmed in the reverse bias voltage regime, while it decreases with increasing distance between an electrode placed on the 2H region and the 2H/1T junction. These results suggest a concentration of high electric field and rapid dissociation of photogenerated excitons at the few-layer lateral Schottky junction, which are beneficial for highly efficien...

A spontaneous symmetry breaking in a system often results in domain wall formation. The motion of such domain walls is utilized to realize novel devices like racetrack-memories, in which moving ferromagnetic domain walls store and carry information. Superconductors breaking time reversal symmetry can also form domains with degenerate chirality of their superconducting order parameter. Sr2RuO4 is the leading candidate of a chiral p-wave superconductor, expected to be accompanied by chiral domain structure. Here, we present that Nb/Ru/Sr2RuO4 topological superconducting-junctions, with which the phase winding of order parameter can be effectively probed by making use of real-space topology, exhibit unusual switching between higher and lower critical current states. This switching is well explained by chiral-domain-wall dynamics. The switching can be partly controlled by external parameters such as temperature, magnetic field and current. These results open up a possibility to utilize the superconducting chiral domain wall motion for future novel superconducting devices.

A spontaneous symmetry breaking in a system often results in domain wall formation. The motion of such domain walls is utilized to realize novel devices like racetrack-memories, in which moving ferromagnetic domain walls store and carry information. Superconductors breaking time reversal symmetry can also form domains with degenerate chirality of their superconducting order parameter. Sr2RuO4 is the leading candidate of a chiral p-wave superconductor, expected to be accompanied by chiral domain structure. Here, we present that Nb/Ru/Sr2RuO4 topological superconducting-junctions, with which the phase winding of order parameter can be effectively probed by making use of real-space topology, exhibit unusual switching between higher and lower critical current states. This switching is well explained by chiral-domain-wall dynamics. The switching can be partly controlled by external parameters such as temperature, magnetic field and current. These results open up a possibility to utilize the superconducting chiral domain wall motion for future novel superconducting devices.

We have fabricated superconducting quantum interference devices (SQUIDs) using Nb/Ru/Sr2RuO4 junctions. The superconducting loop of a Nb-Sr2RuO4 hybrid dc SQUID is composed of Nb, Sr2RuO4 and two Nb/Ru/Sr2RuO4 junctions, and made by building a Nb bridge between two individual Ru micro inclusions on the ab-plane surface of the Ru-Sr2RuO4 eutectic system. We measure the critical current between Nb and Sr2RuO4 parts of such dc-SQUIDs, which oscillates with every flux quantum through the SQUID loop.

We fabricate several unconventional proximity junctions of Sr2RuO4 and Pb with the precise control of the junction configurations achieved using a focused-ion beam. We observe a sharp drop of the critical current just below the transition temperature of the bulk Sr2RuO4 irrespective of Ru arrangement in the junctions. We further demonstrate that the essential configuration giving rise to such an anomalous critical current is a single Pb/Ru/Sr2RuO4 junction. The anomalous suppression is ascribable to a topological transition of the superconducting order parameter of Sr2RuO4.

We have clarified how the enhanced superconductivity, often referred to as the 3-K phase superconductivity, develops in the Sr2RuO4-Ru eutectic system. From the detailed ac and dc susceptibility measurements on well-characterized crystals, we revealed strongly anisotropic shielding, governed by the direction of the screening current dominated within the RuO2 plane rather than by the orientation of the Ru lamellae. The onset temperature of the 3-K phase superconductivity probed by diamagnetic screening is as high as 3.5 K. The temperature dependence of the diamagnetic shielding above around 2 K is well ascribed by the interfacial screening around each Ru lamella. Below around 2 K, the rapid development of the shielding fraction as well as its peculiar esponse to ac and dc magnetic fields are explained by the formation of the Josephson network consisting of inter-lamellar supercurrents., 6 pages, 6 figures, accepted for publication in J. Phys. Soc. Jpn

The mechanism of the 12 C(γ, 3α) reaction for (Li, p )γ-rays has been estimated from a study of 576 stars in nuclear emulsions. By the analysis of the angular distributions and correlation of the α-particles, the multipolarity of the absorption process of (Li, p )γ-rays by the 12 C nucleus can be explained by the mixture of two sorts of interaction E 1 and E 2. This result is consistent with Goward and Wilkins' conclusion, but our experimental data of the angular distribution of the first α-particles show significant forward asymmetry contrary to their backward asymmetry.