arXiv subjects

Naoya Yamaguchi

Publications and source records attributed to Naoya Yamaguchi.

42 records · Page 3Linked to original sources

arXiv2017

First-principles study of electric-field-induced topological phase transition in one-bilayer Bi(111)

Using first-principles calculations, we found the topological phase transition induced by electric fields in one-bilayer Bi(111). The bandgap decreased with increasing electric field strength, and it is closed at 2.1 V/Å. For fields exceeding 2.1 V/Å, the bandgap increased with increasing electric field strength, reaching 0.34 eV at 4.0 V/Å. We computed the $Z_{2}$ invariant that characterizes topological insulator phases. As results, one-bilayer Bi(111) showed a topological phase transition induced by the electric field, from the topological insulator phase to the trivial insulator phase through a Dirac semimetal. This topological phase transition could be applied to novel devices.

cond-mat.mtrl-sci↗

arXiv2017

Strain-induced large spin splitting and persistent spin helix at LaAlO$_3$/SrTiO$_3$ interface

We investigated the effect of the tensile strain on the spin splitting at the n-type interface in LaAlO$_3$/SrTiO$_3$ in terms of the spin-orbit coupling coefficient $α$ and spin texture in the momentum space using first-principles calculations. We found that the $α$ could be controlled by the tensile strain and be enhanced up to 5 times for the tensile strain of 7%, and the effect of the tensile strain leads to a persistent spin helix, which has a long spin lifetime. These results support that the strain effect on LaAlO$_3$/SrTiO$_3$ is important for various applications such as spinFET and spin-to-charge conversion.

cond-mat.mtrl-sci↗

arXiv2016

Factorizations of group determinant in group algebra for any abelian subgroup

We give a further extension and generalization of Dedekind's theorem over those presented by Yamaguchi. In addition, we give two corollaries on irreducible representations of finite groups and a conjugation of the group algebra of the groups which have an index-two abelian subgroups.

math.RT↗

arXiv2016

Capelli elements of the group algebra

Inspired by the Capelli identities for group determinants obtained by Tôru Umeda, we give a basis of the center of the group algebra of any finite group by using Capelli identities for irreducible representations. The Capelli identities for irreducible representations are modifications of the Capelli identity. These identities lead to Capelli elements of the group algebra. These elements construct a basis of the center of the group algebra.

math.RT↗

arXiv2016

An extension and a generalization of Dedekind's theorem

For any given finite abelian group, we give factorizations of the group determinant in the group algebra of any subgroup. The factorizations are an extension of Dedekind's theorem. The extension leads to a generalization of Dedekind's theorem and a simple expression for inverse elements in the group algebra.

math.RT↗

arXiv2016

First-principles Study of Rashba Effect in Ultra-thin Bismuth Surface Alloys

We performed density functional calculations for ultra-thin bismuth surface alloys: surface alloys of bismuth and face-centered cubic metals Bi/$M$(111)-$(\sqrt{3}\times\sqrt{3})R30°$ ($M$=Cu, Ag, Au, Ni, Co, and Fe). Our calculated Rashba parameters for the Bi/Ag are consistent with the previous experimental and theoretical results. We predicted a trend in the Rashba coefficients $α_R$ of bands around the Fermi energy for noble metals as follows: Bi/Ag > Bi/Cu > Bi/Au. As for the transition metals, there is a trend in $α_R$: Bi/Ni > Bi/Co > Bi/Fe. Our finding may lead to design efficient spin-charge conversion materials.

cond-mat.mtrl-sci↗