Toshiya Ideue

Van der Waals interfaces can be formed by layer stacking without regard to lattice constants or symmetries of individual building blocks. We engineered the symmetry of a van der Waals interface of tungsten selenide and black phosphorus and realized in-plane electronic polarization that led to the emergence of a spontaneous photovoltaic effect. Spontaneous photocurrent was observed along the polar direction and was absent in the direction perpendicular to it. The observed spontaneous photocurrent

We have investigated the thermal Hall effect of magnons for various ferromagnetic insulators. For pyrochlore ferromagnetic insulators Lu${}_{2}$V${}_{2}$O${}_{7}$, Ho${}_{2}$V${}_{2}$O${}_{7}$, and In${}_{2}$Mn${}_{2}$O${}_{7}$, finite thermal Hall conductivities have been observed below the Curie temperature ${T}_{C}$. From the temperature and magnetic-field dependencies, it is concluded that magnons are responsible for the thermal Hall effect. The Hall effect of magnons can be well explained b

Polar conductors/superconductors with Rashba-type spin-orbit interaction are potential material platforms for quantum transport and spintronic functionalities. One of their inherent properties is the nonreciprocal transport, where the rightward and leftward currents become inequivalent, reflecting spatial inversion/time-reversal symmetry breaking. Such a rectification effect originating from the polar symmetry has been recently observed at interfaces or bulk Rashba semiconductors, while its mech

The recent development of artificially fabricated van der Waals nanostructures makes it possible to design and control the symmetry of solids and to find novel physical properties and related functionalities. A characteristic physical property reflecting such symmetry breaking is the nonlinear response, which is typically studied as the second harmonic generation of light, although studies have recently expanded to include various transport phenomena. An important aspect of nonlinear transport f

Recent progress in understanding the electronic band topology and emergent topological properties encourage us to reconsider the band structure of well-known materials including elemental substances. Controlling such a band topology by external field is of particular interest from both fundamental and technological viewpoints. Here we report possible signatures of the pressure-induced topological phase transition from a semiconductor to a Weyl semimetal in elemental tellurium probed by transport

This paper investigates the bulk rectification effect under out-of-plane magnetic field in a noncentrosymmetric three-dimensioanl superconductor PbTaSe${}_{2}$. The authors show a giant enhancement of the nonreciprocal magnetotransport during the superconducting transition and a sign reversal.

Transition metal dichalcogenide nanotubes are fascinating platforms for the research of superconductivity due to their unique dimensionalities and geometries. Here we report the diameter dependence of superconductivity in individual WS₂ nanotubes. The superconductivity is realized by electrochemical doping via the ionic gating technique in which the diameter of the nanotube is estimated from the periodic oscillating magnetoresistance, known as the Little-Parks effect. The critical tem

Multiferroic materials have attracted considerable attention owing to their unique magnetoelectric or magnetooptical properties. The recent discovery of few-layer van der Waals multiferroic crystals provides a new research direction for controlling the multiferroic properties in the atomic layer limit. However, research on few-layer multiferroic crystals is limited and the effect of thickness-dependent symmetries on those properties is less explored. In this study, the symmetries and magnetoelec

We have investigated thermoelectric properties of a three-dimensional Rashba system BiTeI. Magnetic-field dependences of the Seebeck effect and Nernst effect show qualitative changes with the Fermi level passing through the bulk Dirac point, indicating that thermoelectric effects can be a good experimental probe for the Fermi surface topology. The quantum oscillations are observed in the thermoelectric effect of BiTeI under a magnetic field, which are also dependent on the Fermi-level positions

BiTeI is a polar semiconductor with gigantic Rashba spin-split bands in bulk. We have investigated the effect of pressure on the electronic structure of this material via magnetotransport. Periods of Shubunikov--de Haas (SdH) oscillations originating from the spin-split outer Fermi surface and inner Fermi surface show disparate responses to pressure, while the carrier number derived from the Hall effect is unchanged with pressure. The associated parameters which characterize the spin-split band

Transition metal dichalcogenides (TMDs) have attracted vast interest as layered semiconductors with high electrical and optical properties. Among them, monolayer MoS 2 is a direct gap semiconductor with its gap energy in the visible range (Fig. 1(a)). Interestingly, excitonic states in monolayer MoS 2 are stabilized owing to the intrinsic two-dimensional nature, and the binding energy reaches several hundred meV.