arXiv subjects

Mineo Saito

Publications and source records attributed to Mineo Saito.

8 recordsLinked to original sources

arXiv2018

Strong Rashba effect in the localized impurity states of halogen-doped monolayer PtSe2

The recent epitaxial growth of 1T-phase of PtSe2 monolayer (ML) has opened a possibility for its novel applications, in particular for spintronics device. However, in contrast to 2H-phase of transition-metal dichalcogenides (TMDs), the absence of spin splitting in the PtSe2 ML may limit the functionality for spintronics application. Through fully-relativistic density-functional theory calculations, we show that large spin splitting can be induced in the PtSe2 ML by introducing a substitutional halogen impurity. Depending on the atomic number (Z) of the halogen dopants, we observe an enhancement of the spin splitting in the localized impurity states (LIS), which is due to the increased contribution of the p-d orbitals coupling. More importantly, we identify very large Rashba splitting in the LIS near Fermi level around the Gamma point characterized by hexagonal warping of the Fermi surface. We show that the Rashba splitting can be controlled by adjusting the doping concentration. Therefore, this work paves a possible way to induce the significant Rashba splitting in the two-dimensional TMDs, which is useful for spintronic devices operating at room temperature.

cond-mat.str-el↗

arXiv2018

First-principles study on thermoelectric properties of half-Heusler compounds CoMSb(M=Sc, Ti, V, Cr, and Mn)

We have performed systematic density functional calculations and evaluated thermoelectric properties, See- beck coefficient and anomalous Nernst coefficient of half-Heusler comounds CoMSb(M=Sc, Ti, V, Cr, and Mn). The carrier concentration dependence of Seebeck coefficients in nonmagnetic compounds are in good agreement with experimental values. We found that the half-metallic ferromagnetic CoMnSb show large anomalous Nernst effect originating from Berry curvature at the Brillouin zone boundary. These results help to understanding for the mechanism of large anomalous Nernst coefficient and give us a clue to design high performance magnetic thermoelectric materials.

cond-mat.mtrl-sci↗

arXiv2017

Defect-induced large spin-orbit splitting in the monolayer of PtSe$_2$

The effect of spin-orbit coupling (SOC) on the electronic properties of monolayer (ML) PtSe$_2$ is dictated by the presence of the crystal inversion symmetry to exhibit spin polarized band without characteristic of spin splitting. Through fully-relativistic density-functional theory calculations, we show that large spin-orbit splitting can be induced by introducing point defects. We calculate stability of native point defects such as a Se vacancy (V$_{\texttt{Se}}$), a Se interstitial (Se$_{i}$), a Pt vacancy (V$_{\texttt{Pt}}$), and a Pt interstitial (Pt$_{i}$), and find that both the V$_{\texttt{Se}}$ and Se$_{i}$ have the lowest formation energy. We also find that in contrast to the Se$_{i}$ case exhibiting spin degeneracy in the defect states, the large spin-orbit splitting up to 152 meV is observed in the defect states of the V$_{\texttt{Se}}$. Our analyses of orbital contributions to the defect states show that the large spin splitting is originated from the strong hybridization between Pt-$d_{x{^2}+y{^2}}+d_{xy}$ and Se-$p_{x}+p_{y}$ orbitals. Our study clarifies that the defects play an important role in the spin splitting properties of the PtSe$_2$ ML, which is important for designing future spintronic devices.

cond-mat.str-el↗

arXiv2017

First-principles study of spin texture and Fermi lines in Bi(111) multi-layer nanofilm

We have performed a fully relativistic first-principles density functional calculation examining the surface state of bismuth (Bi) (111) multi-layer nanofilm, with up to 20 Bi bilayers, and investigated the Rashba effect and spin texture on the Bi surfaces. We have revealed a giant out-of-plane spin states on the Fermi lines, and the maximum value of the out-of-plane spin component being approximately 40% of the magnitude of the total spin. We have also evaluated the Rashba parameter $α_R \simeq 1.9 {\rm eV}\cdot$Åusing the surface state bands which is buried in the bulk state, at -0.32 eV below the Fermi energy.

cond-mat.mtrl-sci↗

arXiv2017

Polarity tuning of spin-orbit-induced spin splitting in two-dimensional transition metal dichalcogenides semiconductors

The established spin splitting in monolayer (ML) of transition metal dichalcogenides (TMDs) that is caused by inversion symmetry breaking is dictated by mirror symmetry operations to exhibit fully out-of-plane direction of spin polarization. Through first-principles density functional theory calculations, we show that polarity-induced mirror symmetry breaking leads to new sizable spin splitting having in-plane spin polarization. These splittings are effectively controlled by tuning the polarity using biaxial strain. Furthermore, the admixtures of the out-of-plane and in-plane spin-polarized states in the strained polar systems are identified, which is expected to influence the spin relaxation through the Dyakonov-Perel mechanism. Our study clarified that the polarity-induced mirror symmetry breaking plays an important role in controlling the spin splitting and spin relaxation in the TMDs ML, which is useful for designing future spintronic devices.

cond-mat.str-el↗

arXiv2016

Strain-controlled spin splitting in the conduction band of monolayer WS2

Spin splitting bands that arises in conduction band minimum (CBM) of WS2 monolayer (ML) play an important role in the new spin-orbit phenomena such as spin-valley coupled electronics. However, application of strain strongly modifies electronic properties of the WS2 ML, which is expected to significantly affect to the properties of the spin splitting bands. Here, by using fully-relativistic first-principles calculations based on density-functional theory, we show that a substantial spin spliting bands observed in the CBM is effectively controlled and tuned by applying the biaxial strain. We also find that these spin splitting bands induce spin textures exhibiting fully out-of-plane spin polarization in the opposite direction between the K and Q points and their time reversals in the first Brillouin zone. Our study clarify that the strain plays an significant role in the spin-orbit coupling of the WS2 ML, which has very important implications in designing future spintronics devices.

cond-mat.str-el↗

arXiv2015

Persistent spin helix on a wurtzite ZnO(10-10) surface: First-principles density-functional study

The persistent spin helix (PSH) that has been widely and exclusively studied in zinc-blende structures is revealed for the first time on the surface of a wurtzite structure. Through first-principles calculations of the ZnO(10-10) surface, a quasi-one dimensional orientation of the spin textures is identified. Further, the wavelength of this particular PSH is smaller than that observed with various zinc-blende quantum well structures, thus indicating that wurtzite-structured surfaces are suitable for spintronics applications.

cond-mat.mes-hall↗

arXiv2014

First-principles study of Exchange Interaction in Ising-type Multiferroic Ca$_3$CoMnO$_6$

We perform first-principles calculations of multiferroic Ca$_3$CoMnO$_6$ and evaluate the exchange coupling constants using the Green's function method. We clarify the effect of intra-chain and inter-chain exchange interactions on magnetic stability. We find that inter-chain exchange coupling constants are antiferromagnetic and that there are geometrical frustrations in the triangular lattices of magnetic chains in Ca$_3$CoMnO$_6$. The magnetic transition temperature is evaluated using effective Hamiltonian with calculated exchange coupling constants. We obtain the transition temperature 5.80K. The value has the same order as that of experimentally observed.

cond-mat.str-el↗