Rai Moriya

The spin-orbit interaction (SOI) of a two-dimensional hole gas in the inversion symmetric semiconductor Ge is studied in a strained-Ge/SiGe quantum well structure. We observe weak antilocalization (WAL) in the magnetoconductivity measurement, revealing that the WAL feature can be fully described by the k-cubic Rashba SOI theory. Furthermore, we demonstrate electric field control of the Rashba SOI. Our findings reveal that the heavy hole (HH) in strained Ge is a purely cubic Rashba system, which

Graphene-based vertical field effect transistors have attracted considerable attention in the light of realizing high-speed switching devices; however, the functionality of such devices has been limited by either their small ON-OFF current ratios or ON current densities. We fabricate a graphene/MoS2/metal vertical heterostructure by using mechanical exfoliation and dry transfer of graphene and MoS2 layers. The van der Waals interface between graphene and MoS2 exhibits a Schottky barrier, thus en

We demonstrate 3D mechanical manipulations, such as sliding, rotating, folding, flipping, and exfoliating, of 2D materials using a microdome polymer (MDP) via in situ real-time observation with an optical microscope. A dimethylpolysiloxane (PDMS)-based MDP is covered with a poly(vinyl chloride) (PVC) adhesion layer. This PVC-MDP structure enables us to achieve small and adjustable contact areas between the PVC-MDP and a 2D-material flake, which is typically between ∼10 and ∼100 μm in diameter. T

We demonstrated n-type and p-type carrier injections into a transition metal dichalcogenide (TMD) WSe2 using van der Waals (vdW) contacts of two-dimensional (2D) materials: graphite for an n-type contact and NbSe2 for a p-type contact. Instead of conventional methods such as the evaporation of metals on TMD, 2D metals were transferred onto WSe2 in order to form van der Waals contacts. With these contacts, we demonstrated a small Schottky barrier height for both carrier polarities. Our finding re

We performed detailed studies of the current–voltage (I–V) characteristics in graphene/MoS2/metal vertical field-effect transistors. Owing to its low density of states, the Fermi level in graphene is very sensitive to its carrier density and thus the external electric field. Under the application of a bias voltage VB between graphene and the metal layer in the graphene/MoS2/metal heterostructure for driving current through the van der Waals interface, the electric field across the MoS2 dielectri

This study demonstrates a low-temperature Ohmic contact to WSe2 using a van der Waals (vdW) junction between highly p-doped MoS2 (p+-MoS2) and WSe2. p+-MoS2 exhibits a large work function comparable to that of a well-known metal such as Pt. Owing to its layered crystal structure, p+-MoS2 can easily be exfoliated to obtain atomically flat, freshly cleaved surfaces. Moreover, it is stable in air; therefore, this material can be used as an efficient hole-injection contact to a transition metal dich

The velocity of vortex domain walls (DWs) was measured versus magnetic field in Ni65Fe20Co15 nanowires with different widths and thicknesses using time-resolved anisotropic magnetoresistance measurements. The Walker breakdown field, which separates translational and precessional DW propagation regimes, decreases for wider and thicker nanowires. On the contrary, the peak velocity at the Walker breakdown field is independent of the nanowire width and thickness. The Gilbert damping parameter α was

Few-layer transition metal dichalcogenides (TMDs) exhibit out-of-plane wave function confinement with subband quantization. This phenomenon is totally absent in monolayer crystals and is regarded as resulting from a naturally existing van der Waals quantum-well state. Because the energy separation between the subbands corresponds to the infrared wavelength range, few-layer TMDs are attractive for their potential to facilitate the application of TMD semiconductors as infrared photodetectors and e

We investigate the transport properties of the van der Waals (vdW) junction between a layered superconductor $\mathrm{Nb}{\mathrm{Se}}_{2}$ and a graphene. A superconductor/graphene (S/G) vdW junction is fabricated by dry transferring a freshly exfoliated $\mathrm{Nb}{\mathrm{Se}}_{2}$ flake onto a graphene surface. This vdW junction provides a transparent superconductor/graphene contact as well as metal-induced doping in the graphene layer underneath, thereby facilitating vdW coupling-induced s

Detail transport properties of graphene/MoS2/metal vertical heterostructure have been investigated. The van der Waals interface between the graphene and MoS2 exhibits Schottky barrier. The application of gate voltage to the graphene layer enables us to modulate the Schottky barrier height; thus gives rise to the control of the current flow across the interface. By analyzing the temperature dependence of the conductance, the modulation of Schottky barrier height {\Delta}{\phi} has been directly d

We report current-induced magnetization reversal in a ferromagnetic semiconductor-based magnetic tunnel junction (Ga,Mn)As/AlAs/(Ga,Mn)As prepared by molecular beam epitaxy on a p -GaAs(001) substrate. A change in magneto-resistance that is asymmetric with respect to the current direction is found with the excitation current of 10 6 A/cm 2 . Contributions of both unpolarized and spin-polarized components are examined, and we conclude that the partial magnetization reversal occurs in the (Ga,Mn)A

Bloch electrons lacking inversion symmetry exhibit orbital magnetic moments owing to the rotation around their center of mass; this moment induces a valley splitting in a magnetic field. For the graphene/h-BN moiré superlattice, inversion symmetry is broken by the h-BN. The superlattice potential generates a series of Dirac points (DPs) and van Hove singularities (vHSs) within an experimentally accessible low energy state, providing a platform to study orbital moments with respect to band struct

We demonstrated exfoliated-graphene/transition metal dichalcogenide (TMD)/metal vertical field-effect transistor (vFET). The van der Waals junction between graphene and TMD exhibit Schottky barrier. Owing to the low density of state of graphene, the position of graphene’s Fermi level can be modulated by the external electric field, thus enable us electric field modulation of Schottky barrier height at graphene/TMD interface. Based on this mechanism, a vertical transport in the heterostructure ex