1998 Fiscal Year Annual Research Report

電子型高温超伝導体単結晶におけるスピン・電荷秩序と電荷ダイナミクス

Research Project

Project/Area Number	10440100
Research Institution	The University of Tokyo
Principal Investigator	十倉好紀東京大学, 大学院・工学系研究科, 教授 (30143382)
Co-Investigator(Kenkyū-buntansha)	田口康二郎東京大学, 大学院・工学系研究科, 助手 (70301132)
Keywords	電子型高温超伝導体 / 還元処理 / 頂点酸素 / 不純物 / 反強磁性 / 光学伝導度 / 擬ギャップ / 格子異常
Research Abstract	今年度はNd_<2-x>Ce_xCuO_<>4+yの単結晶をTraveling Solvent Floating Zone法で作製し、光学伝導度スペクトルおよびラマン散乱スペクトルを測定することによってその電荷・格子ダイナミクスの温度依存性を調べた。x=0.15の、酸素雰囲気中でアニールされて超伝導を示さない試料と、アルゴン雰囲気中でアニールされて超伝導を示す試料の両方について測定を行った。超伝導を示さない試料についてのみ、低温で光学伝導度の中赤外領域に擬ギャップ的な構造が現れることが見出された。この擬ギャップ的構造は、0.3eV付近を等吸収点とし、スペクトラルウェイトの移動は0.8eV程度にまで及んでいる。この構造は400K程度から温度を下げてくると、340K程度で現れはじめ、100K以下程度で飽和するような温度依存性を示す。また、遠赤外領域のフォノンスペクトルにおいても、超伝導を示さない試料についてのみ異常が観測された。すなわち、400Kにおいては、正方晶の対称性から予想される4本のフォノンが存在しているが、340K以下では温度の低下とともにペンディングモードの周りの振動子強度が増大し、フォノンピークが分裂する様子が観測された。これらの擬ギャップ的な構造およびフォノンモードの異常は同様の温度依存性を示し、共通の起源によるものであることを示唆している。また、これらの異常は典型的な電荷整列系であるMn,Ni,Fe酸化物等において観測されている異常と同様なものであることから、超伝導を示さないNd_<2-x>Ce_xCuO_<4+y>結晶においても電荷整列またはその揺らぎが存在することが示唆される。

Research Products
(29 results)

All Other

All Publications (29 results)

[Publications] Y.Tokura: "Thermally-induced insulator-metal transition in LaCoO_3: a view based on Mott tran-sition" Phys.Rev.B. 58. R1699-R1702 (1998)
[Publications] A.Asamitsu: "Hall effect in La_<1-x>Sr_xMnO_3" Phys.Rev.B. 58. 47-50 (1998)
[Publications] S.Yamaguchi: "Magneto-optical Kerr effects in perovskite-type transition-metal oxides: La_<1-x>Sr_xMnO_3 and La_<1-x>Sr_xCoO_3" Phys.Rev.B. 58. 6862-6870 (1998)
[Publications] M.Fiebig: "Visualization of the local insulator-metal transition in Pr_<0.7>Ca_<0.3>MnO_3" Science. 280. 1925-1928 (1998)
[Publications] K.Ogawa: "Stability of photoinduced insulator-metal transition in Pr_<1-x>Ca_xMnO_3" Phys.Rev.B. 57. R15033-R15036 (1998)
[Publications] Y.Murakami: "Resonant x-ray scattering from orbital ordering in LaMnO_3" Phys.Rev.Lett.81. 582-585 (1998)
[Publications] Y.Tokura: "Spin-coupled charge dynamics in layered manganite crystals" J.Korean Phys.Soc.33. 168-173 (1998)
[Publications] H.Yoshizawa: "Anisotropic spin waves in a metallic antiferromagnet Nd_<0.45>Sr_<0.55>MnO_3" Phys.Rev.B. 58. R571-R574 (1998)
[Publications] R.H.Heffner: "Effects of reduced dimensionality on spin dynamics in the layered perovskite La_<1.4>Sr_<1.6>Mn_2O_7" Phys.Rev.Lett.81. 1706-1709 (1998)
[Publications] S.K.Park: "Charge-gap formation upon the Verwey transition in Fe_3O_4" Phys.Rev.B. 58. 3717-3720 (1998)
[Publications] D.S.Dessau: "k-dependent electronic structure, a large ‘ghost' Fermi surface, and a pseudogap in a layered magnetoresistive oxide" Phys.Rev.Lett.81. 192-196 (1998)
[Publications] K.-I.Kobayashi: "Room-temperature magnetoresistance in an oxide material with an ordered double-perovskite structure" Nature. (1998)
[Publications] M.Izumi: "Atomically defined epitaxy and physical properties of strained La_<0.6>Sr_<0.4>MnO_3 films" Appl.Phys.Lett.(1998)
[Publications] T.Okuda: "Critical behavior of metal-insulator transition in La_<1-x>Sr_xMnO_3" Phys.Rev.Lett.(1998)
[Publications] T.Kimura: "Successive structural transitions coupled with magneto-transport properties in LaSr_2Mn_2O_7" Phys.Rev.B. (1998)
[Publications] T.Ishikawa: "Optical spectroscopy of charge-ordering transition in La_<1/3>Sr_<2/3>FeO_3" Phys.Rev.B. (1998)
[Publications] A.V.Puchkov: "New ARPES results on Sr_2RuO_4: Fermi surface revisited" Phys.Rev.B. (1998)
[Publications] Y.Konishi: "Fabrication and physical properties of c-axis oriented thin films of layered perovskite La_<2-2x>Sr_<1+2x>Mn_2O_7" Appl.Phys.Lett.(1998)
[Publications] R.Kumai: "Band-filling control of π-d electron system based on bis (ethylenedithio) tetrathiaful-valene cation radical salts" J.American Chem.Soc.120. 8263-8264 (1998)
[Publications] S.Horiuchi: "Chemical control of ferroelectric neutral-ionic transition in charge-transfer complexes, TTF_<1-x>TSF_xQCl_4 [TTF=tetrathiafulvalene; TSF=tetraselenafulvalene; QCl_4=p-chloranil]" J.American Chem.Soc.120. 7379-7380 (1998)
[Publications] M.Imada: "Metal-insulator transitions" Rev.Mod.Phys.70. 1039-1263 (1998)
[Publications] Y.Tokura: "Optical and magnetic properties of transition metal oxides" Current Opinion in Solid state and materials science. 3. 175-180 (1998)
[Publications] J.Q.Li: "Structural properties and charge-ordering transition in LaSr_2Mn_2O_7" Phys.Rev.B. 57. R3205-R3208 (1998)
[Publications] K.Yamamoto: "Raman scattering of the charge-spin stripes in La_<1.67>Sr_<0.33>NiO_4" Phys.Rev.Lett.80. 1493-1496 (1998)
[Publications] M.Tokunaga: "High-magnetic-field study of the phase transitions of R_<1-x>Ca_xMnO_3 (R=Pr,Nd)" Phys.Rev.B. 57. 5259-5264 (1998)
[Publications] Y.Murakami: "Direct observation of charge and orbital ordering in La_<0.5>Sr_<1.5>MnO_4" Phys.Rev.Lett.80. 1932-1935 (1998)
[Publications] T.Ishikawa: "Optical probe of anisotropic and incoherent charge dynamics in a layered ferromagnet: La_<1.2>Sr_<1.8>Mn_2O_7" Phys.Rev.B. 57. R8079-R8082 (1998)
[Publications] Y.Okimoto: "Charge ordering and disordering transitions in Pr_<1-x>Ca_xMnO_3 (x=0.4) as investigated by optical spectroscopy" Phys.Rev.B. 57. R9377-R9380 (1998)
[Publications] H.Kuwahara: "Giant magnetoresistance and related properties of metal oxides" World Scientific Co.,Singapore, (1998)

1998 Fiscal Year Annual Research Report

電子型高温超伝導体単結晶におけるスピン・電荷秩序と電荷ダイナミクス

Principal Investigator

十倉 好紀 東京大学, 大学院・工学系研究科, 教授 (30143382)

Research Products

[Publications] Y.Tokura: "Thermally-induced insulator-metal transition in LaCoO_3: a view based on Mott tran-sition" Phys.Rev.B. 58. R1699-R1702 (1998)

[Publications] A.Asamitsu: "Hall effect in La_<1-x>Sr_xMnO_3" Phys.Rev.B. 58. 47-50 (1998)

[Publications] S.Yamaguchi: "Magneto-optical Kerr effects in perovskite-type transition-metal oxides: La_<1-x>Sr_xMnO_3 and La_<1-x>Sr_xCoO_3" Phys.Rev.B. 58. 6862-6870 (1998)

[Publications] M.Fiebig: "Visualization of the local insulator-metal transition in Pr_<0.7>Ca_<0.3>MnO_3" Science. 280. 1925-1928 (1998)

[Publications] K.Ogawa: "Stability of photoinduced insulator-metal transition in Pr_<1-x>Ca_xMnO_3" Phys.Rev.B. 57. R15033-R15036 (1998)

[Publications] Y.Murakami: "Resonant x-ray scattering from orbital ordering in LaMnO_3" Phys.Rev.Lett.81. 582-585 (1998)

[Publications] Y.Tokura: "Spin-coupled charge dynamics in layered manganite crystals" J.Korean Phys.Soc.33. 168-173 (1998)

[Publications] H.Yoshizawa: "Anisotropic spin waves in a metallic antiferromagnet Nd_<0.45>Sr_<0.55>MnO_3" Phys.Rev.B. 58. R571-R574 (1998)

[Publications] R.H.Heffner: "Effects of reduced dimensionality on spin dynamics in the layered perovskite La_<1.4>Sr_<1.6>Mn_2O_7" Phys.Rev.Lett.81. 1706-1709 (1998)

[Publications] S.K.Park: "Charge-gap formation upon the Verwey transition in Fe_3O_4" Phys.Rev.B. 58. 3717-3720 (1998)

[Publications] D.S.Dessau: "k-dependent electronic structure, a large ‘ghost' Fermi surface, and a pseudogap in a layered magnetoresistive oxide" Phys.Rev.Lett.81. 192-196 (1998)

[Publications] K.-I.Kobayashi: "Room-temperature magnetoresistance in an oxide material with an ordered double-perovskite structure" Nature. (1998)

[Publications] M.Izumi: "Atomically defined epitaxy and physical properties of strained La_<0.6>Sr_<0.4>MnO_3 films" Appl.Phys.Lett.(1998)

[Publications] T.Okuda: "Critical behavior of metal-insulator transition in La_<1-x>Sr_xMnO_3" Phys.Rev.Lett.(1998)

[Publications] T.Kimura: "Successive structural transitions coupled with magneto-transport properties in LaSr_2Mn_2O_7" Phys.Rev.B. (1998)

[Publications] T.Ishikawa: "Optical spectroscopy of charge-ordering transition in La_<1/3>Sr_<2/3>FeO_3" Phys.Rev.B. (1998)

[Publications] A.V.Puchkov: "New ARPES results on Sr_2RuO_4: Fermi surface revisited" Phys.Rev.B. (1998)

[Publications] Y.Konishi: "Fabrication and physical properties of c-axis oriented thin films of layered perovskite La_<2-2x>Sr_<1+2x>Mn_2O_7" Appl.Phys.Lett.(1998)

[Publications] R.Kumai: "Band-filling control of π-d electron system based on bis (ethylenedithio) tetrathiaful-valene cation radical salts" J.American Chem.Soc.120. 8263-8264 (1998)

[Publications] S.Horiuchi: "Chemical control of ferroelectric neutral-ionic transition in charge-transfer complexes, TTF_<1-x>TSF_xQCl_4 [TTF=tetrathiafulvalene; TSF=tetraselenafulvalene; QCl_4=p-chloranil]" J.American Chem.Soc.120. 7379-7380 (1998)

[Publications] M.Imada: "Metal-insulator transitions" Rev.Mod.Phys.70. 1039-1263 (1998)

[Publications] Y.Tokura: "Optical and magnetic properties of transition metal oxides" Current Opinion in Solid state and materials science. 3. 175-180 (1998)

[Publications] J.Q.Li: "Structural properties and charge-ordering transition in LaSr_2Mn_2O_7" Phys.Rev.B. 57. R3205-R3208 (1998)

[Publications] K.Yamamoto: "Raman scattering of the charge-spin stripes in La_<1.67>Sr_<0.33>NiO_4" Phys.Rev.Lett.80. 1493-1496 (1998)

[Publications] M.Tokunaga: "High-magnetic-field study of the phase transitions of R_<1-x>Ca_xMnO_3 (R=Pr,Nd)" Phys.Rev.B. 57. 5259-5264 (1998)

[Publications] Y.Murakami: "Direct observation of charge and orbital ordering in La_<0.5>Sr_<1.5>MnO_4" Phys.Rev.Lett.80. 1932-1935 (1998)

[Publications] T.Ishikawa: "Optical probe of anisotropic and incoherent charge dynamics in a layered ferromagnet: La_<1.2>Sr_<1.8>Mn_2O_7" Phys.Rev.B. 57. R8079-R8082 (1998)

[Publications] Y.Okimoto: "Charge ordering and disordering transitions in Pr_<1-x>Ca_xMnO_3 (x=0.4) as investigated by optical spectroscopy" Phys.Rev.B. 57. R9377-R9380 (1998)

[Publications] H.Kuwahara: "Giant magnetoresistance and related properties of metal oxides" World Scientific Co.,Singapore, (1998)

十倉好紀東京大学, 大学院・工学系研究科, 教授 (30143382)