有機導体における強い相関をもつ低次元電子系の研究

1991 年度 実績報告書

• 研究課題/領域番号: 03302017
• 研究機関: 東京大学
• 研究代表者: 鹿児島 誠一 東京大学, 教養学部, 教授 (30114432)
• 研究分担者: 大嶋 孝吉 岡山大学, 理学部, 助教授 (10114414) ; 高田 慧 筑波大学, 物理学系, 教授 (10015779) ; 石黒 武彦 京都大学, 理学部, 教授 (50202982) ; 梶田 晃示 東邦大学, 理学部, 教授 (50011739) ; 豊田 直樹 東北大学, 金属材料研究所, 助教授 (50124607)
• キーワード: 有機導体 / 電子相関 / 抵次元電子 / 電気伝導 / 電荷密度 / スピン密度 / 磁気抵抗 / 価数揺動

研究概要

この研究の目的は、低次元電子系をもつ有機導体において、電子間ク-ロン相関が低次元電子のふるまいに与える影響を明らかにすることである。今年度は主に、DCNQIーCu塩とBEDTーTTF塩に関する研究を集中的に進めた。
DCNQIーCu塩については、低温・強磁場での電気的測定、磁気抵抗測定、静磁化率測定とESR、NMR測定によって電荷とスピン状態を探るほか、XANESスペクトル測定によってCuイオンのまわりの構造変化と電気的・磁気的性質との関係を調べた。また比熱測定によって、金属ー絶縁体転移近傍での電子系の状態密度の変化を調べ、いわゆる「重い電子系」ができている可能性を指摘した。理論的には、周期的アンダ-ソン模型に電子ー格子相互作用を取りいれ、Cuの混合原子価が原因で生じるスピン密度と電荷密度分共存状態を明らかにした。
BEDTーTTF系物質では、特に(BEDTーTTF)_2KHg(SCN)_4の低温低磁場で磁気抵抗に見られる特異な状態を調べ、そこでは反強磁性状態が現れていることを発見した。しかしながら、NMR測定によるとこの状態は通常の反強磁性とは考えにくい。また、このことによって磁気抵抗などに見られる異常が説明できるかどうかは、今後の問題である。
また、αー(BEDTーTTF)_2I_3の金属ー非金属転移について、比熱や高圧下の磁気抵抗を測定し、磁場によってこの転移が引き起こされている可能性があることを明らかにした。

研究成果

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