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Superconductivity and antiferromagnetism in the three-dimensional Hubbard model

3次元ハバード模型における超伝導と反強磁性

瀧本 哲也; 守谷 亨*

Takimoto, Tetsuya; Moriya, Toru*

異方的なホッピング行列$$t_{rm z}$$$$t_{perp}$$を持つ3次元ハバード模型に対して、ハーフフィリング近傍における反強磁性と超伝導の間の関係を研究した。一種のスピンゆらぎ理論であるゆらぎ交換近似を使って、さまざまな$$r_{rm z}=t_{rm z}/t_{perp}$$の値に対して相図を計算した。$$r_{rm z}$$の増大に伴って、ハーフフィリング電子密度の周りの反強磁性相は広がるが、一方で、それに隣接した異方的な$$d_{x^{2}-y^{2}}$$-波超伝導相は縮まる。適度な$$r_{rm z}$$の値に対して、われわれは低温で$$d_{x^{2}-y^{2}}$$-波超伝導相から非整合スピン密度波と$$d_{x^{2}-y^{2}}$$-波超伝導の共存相への二次転移を見つけた。この共存相に近づくと、非整合スピン密度波の波数を持つスピンゆらぎのソフト化された成分が発達する。

Interplay between antiferromagnetism and superconductivity is studied by using the 3-dimensional nearly half-filled Hubbard model with anisotropic transfer matrices $$t_{rm z}$$ and $$t_{perp}$$. The phase diagrams are calculated for varying values of the ratio $$r_{rm z}=t_{rm z}/t_{perp}$$ using the spin fluctuation theory within the fluctuation-exchange approximation. The antiferromagnetic phase around the half-filled electron density expands while the neighboring phase of the anisotropic $$d_{x^{2}-y^{2}}$$-wave superconductivity shrinks with increasing $$r_{rm z}$$. For moderate values of $$r_{rm z}$$ we find the second order transition, with lowering temperature, from the $$d_{x^{2}-y^{2}}$$-wave superconducting phase to a phase where incommensurate SDW coexists with $$d_{x^{2}-y^{2}}$$-wave superconductivity. Soft components of the incommensurate SDW spin fluctuation mode grow as the coexistent phase is approached.

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パーセンタイル:75.42

分野:Materials Science, Multidisciplinary

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