Tomoki Machida

Supercurrent flow between two superconductors with different order parameters, a phenomenon known as the Josephson effect, can be achieved by inserting a non-superconducting material between two superconductors to decouple their wavefunctions. These Josephson junctions have been employed in fields ranging from digital to quantum electronics, yet their functionality is limited by the interface quality and use of non-superconducting material. Here we show that by exfoliating a layered dichalcogeni

Coherent control of local nuclear spins in a solid-state device is demonstrated. By unequally populating spin-resolved quantum-Hall edge channels, nuclear spins in a limited region along the edge channels are strongly polarized via the hyperfine interaction. Pulsed rf magnetic fields, generated by a built-in micrometal strip, cause the nuclear-spin state to evolve coherently. The nuclear-spin state reached during the pulse duration is finally read out via the edge-channel conductance, which show

Abstract The fascinating point of 2D and layered materials is that they can be assembled into van der Waals (vdW) heterostructures, in which atomic layers are integrated by vdW force. There are almost infinite potential combinations in vdW heterostructures owing to the multiple degrees of freedom, i.e., the choice of materials, stacking order, and lateral orientation angle at the interfaces. In this article, we review the fabrication technique of vdW heterostructures, which has played an essenti

We manipulate and detect local nuclear spin polarization in integer quantum Hall (IQH) systems using micrometal strips fabricated on top of Al0.3Ga0.7As/GaAs Hall bar devices. The radio-frequency (rf) magnetic fields generated by transmitting rf electrical currents through the micrometal strips causes nuclear magnetic resonance in a limited region along IQH edge channels, and resulting changes in the nuclear spin polarization are detected via Hall resistance of the devices.

We find that the scattering between unequally populated fractional quantum Hall (FQH) edge channels (EC's) polarizes nuclear spins through the hyperfine interaction. This dynamic nuclear polarization (DNP) is evidenced by the nuclear magnetic resonance detected via the transport through FQH EC's. Spin polarizations of different FQH EC's are inferred from the polarity of DNP.

Hexagonal boron nitride (h-BN) crystals grown under ultrahigh pressures and ultrahigh temperatures exhibit a high crystallinity and are used throughout the world as ideal substrates and insulating layers in van der Waals heterostructures. However, in their central region, these crystals have domains which contain a significant density of carbon impurities. In this study, we utilized cathodoluminescence and far-ultraviolet photoluminescence to reveal that the carbon (C)-rich domain can exist even

Hexagonal boron nitride (h-BN) synthesized under high pressure and high temperature (HPHT) has been used worldwide in two-dimensional (2D) materials research as an essential material for constructing van der Waals heterostructures. Here, we study h-BN synthesized with another method, i.e., via synthesis at <i>atmospheric</i> pressure and high temperature (APHT) using a metal alloy solvent. First, we examine the APHT h-BN in a bulk crystal form using cathodoluminescence and find that it does not

We report the first cyclotron resonance study of monolayer graphene under double-moiré potentials in which the crystal axis of graphene is nearly aligned to those of both the top and bottom hexagonal boron nitride (h-BN) layers. Under mid-infrared light irradiation, we observe cyclotron resonance absorption with the following unique features: (1) cyclotron resonance magnetic field BCR is entirely different from that of nonaligned monolayer graphene, (2) BCR exhibits strong electron–hole asymmetr

Rhenium dinitride (ReN2) is a newly synthesized layered transition metal dinitride. We present the first experimental investigation of the electrical transport properties of ReN2 by exfoliating the ReN2 crystal into thin films. The carrier transport measurements reveal that ReN2 is a metal. Furthermore, ReN2 exhibits suppression of resistance due to superconductivity at temperatures below 10 K. The critical magnetic fields differ significantly depending on the direction of the applied magnetic f

Resistance fluctuations in integer and fractional quantum Hall transitions are studied in modulation-doped ${\mathrm{Al}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ heterostructures. We examine the role of coherence in the fluctuations by investigating the conductance through two scattering regions that are spatially separated but interact quantum-mechanically with each other. Though the conductor is in a coherent regime, the phase coherence is found t

Landau levels (LLs) of ABA-stacked trilayer graphene (TLG) are described as the combination of monolayer graphene-like LLs and bilayer graphene-like LLs. They are extremely sensitive to the applied perpendicular electric displacement field <i>D</i>. Here, we demonstrate the electrical control of cyclotron resonance (CR) in a dual-gated ABA-stacked TLG. Under the irradiation of mid-infrared light, we observed the photovoltage induced by the CR absorption through the photothermoelectric effect. Th

We study the transition between successive integer quantum-Hall effect plateaus, using ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/GaAs heterostructure Hall bars with different-size Schottky front gates at low temperatures down to 25 mK. The transition width decreases with increasing length as well as the width of the two-dimensional electron-gas regions below the gates. The critical exponent of the localization length as well as the size and the temperatur

Polar materials are interesting platforms for fundamental research because they exhibit the spontaneous electric polarization (SEP) and the shift current photovoltaic effect, both originating from the inherent Berry connection. Owing to the electrical controllability, these phenomena are often studied in ferroelectric materials. Recently, the SEP and the shift current are enthusiastically studied in two-dimensional materials, but an electrical control has not been realized. In this study, we obs