arXiv subjects

Nobuya Sato

Publications and source records attributed to Nobuya Sato.

5 recordsLinked to original sources

arXiv2020

Coexistence of spontaneous polarization and superconductivity in hole-doped oxyhydrides ATiO_2H (A=K, Rb, Cs): first-principles study

The polar metal is a material that hosts both polar distortion and metallicity. Such a material is expected to show exotic magneto-electric phenomena if superconducts. Here, we theoretically explore ferroelectric and superconducting properties in a series of perovskite-type oxyhydrides ATiO$_2$H (A=K, Rb, Cs) under hole-doping conditions using the first-principles calculations based on the density functional theory. Our simulation shows that these compounds host spontaneous polarization and superconductivity at optimal doping concentration. The unusual coexistence of superconductivity and large polarization (~100 $μ$C/cm$^2$) originates from weak coupling of the polar distortion and superconducting states, the reason of which is separation of the displaced atoms and spacially confined metallic carriers. Besides, the superconductivity is enhanced by the unique electronic properties near the valence band maximum: quartic band dispersion with a sizable contribution of hydrogen 1s states. Our study thus feature the oxyhydrides as possible model polar superconducting systems, which may be utilizable for future magneto-electric devices.

cond-mat.supr-con↗

arXiv2004

Orbifold aspects of the Longo-Rehren subfactors

In this article, we will prove that the subsectors of $α$-induced sectors for $M \rtimes \hat{G} \supset M$ forms a modular category, where $M \rtimes \hat{G}$ is the crossed product of $M$ by the group dual $\hat{G}$ of a finite group $G$. In fact, we will prove that it is equivalent to Müger's crossed product. By using this identification, we will exhibit an orbifold aspect of the quantum double of $Δ$(not necessarily non-degenerate) obtained from a Longo-Rehren inclusion $A \supset B_Δ$ under certain assumptions. We will apply the above description of the quantum double of $Δ$ to the Reshetikhin-Turaev topological invariant of closed 3-manifolds, and we obtain a simpler formula, which is a degenerate version of Turaev's theorem that the Reshetikhin-Turaev invariant for the quantum double of a modular category $\hatΔ$ is the product of Reshetikhin-Turaev invariant of $\hatΔ$ and its complex conjugate.

math.OA↗

arXiv2003

(2+1)-dimensional topological quantum field theory with a Verlinde basis and Turaev-Viro-Ocneanu invariants of 3-manifolds

In this article, we discuss a (2+1)-dimensional topological quantum field theory, for short TQFT, with a Verlinde basis. As a conclusion of this general theory, we have a Dehn surgery formula. We show that Turaev-Viro-Ocneanu TQFT has a Verlinde basis. Several applications of this theorem are exposed. Based on Izumi's data of subfactors, we list several computations of Turaev-Viro-Ocneanu invariants for some 3-manifolds.

math.QA↗

arXiv2002

(2+1)-dimensional topological quantum field theory from subfactors and Dehn surgery formula for 3-manifold invariants

In this paper, we establish the general theory of (2+1)-dimensional topological quantum field theory (in short, TQFT) with a Verlinde basis. It is a consequence that we have a Dehn surgery formula for 3-manifold invariants for this kind of TQFT's. We will show that Turaev-Viro-Ocneanu unitary TQFT's obtained from subfactors satisfy the axioms of TQFT's with Verlinde bases. Hence, in a Turaev-Viro-Ocneanu TQFT, we have a Dehn surgery formula for 3-manifolds. It turns out that this Dehn surgery formula is nothing but the formula of the Reshetikhin-Turaev invariant constructed from a tube system, which is a modular category corresponding to the quantum double construction of a C^*-tensor category. In the forthcoming paper, we will exbit computations of Turaev-Viro-Ocneanu invariants for several ``basic 3-manifolds ''. In Appendix, we discuss the relationship between the system of M_{infinity}-M_{infinity} bimodules arising from the asymptotic inclusion M V M^{op} subset M_{infinity} constructed from N subset M and the tube system obtained from a subfactor N subset M.

math.OA↗

arXiv2002

Computations of Turaev-Viro-Ocneanu invariants of 3-manifolds from subfactors

In this paper, we establish a rigorous correspondence between the two tube algebras, that one comes from the Turaev-Viro-Ocneanu TQFT introduced by Ocneanu and another comes from the sector theory introduced by Izumi, and construct a canonical isomorphism between the centers of the two tube algebras, which is a conjugate linear isomorphism preserving the products of the two algebras and commuting with the actions of SL(2,Z). Via this correspondence and the Dehn surgery formula, we compute Turaev-Viro-Ocneanu invariants from several subfactors for basic 3-manifolds including lens spaces and Brieskorn 3-manifolds by using Izumi's data written in terms of sectors.

math.OA↗