1 2014/09/22 䜾䝹䞊䝥䝉䝭䝘䞊 ྡྂᒇᏛ 㧗ᔱ䞉ఀ⸨◊✲ᐊ M1 Ἑෆ❶࿃ ⫼ᬒ 2 •⇕ ⇕㟁ኚᮦᩱ䛸䛿䞉䞉䞉 ᅛయ䛻 ᗘᕪ䜢䛘䜛䛣䛸䛷㉳㟁ຊ䛜⏕ 䛨䜛䝊䞊䝧䝑䜽ຠᯝ䜢⏝䛧䚸⇕䜶䝛䝹䜼䞊 䛸㟁Ẽ䜶䝛䝹䜼䞊䜢䛔䛻ኚ䛩䜛ᮦᩱ䚹 䞉⇕㟁ᛶ⬟ᣦᩘ ᅗ䚸⇕㟁ኚ䝰䝆䝳䞊䝹 (http://www.logsoku.com/r/poverty/1380207867/) ⇕㟁ᮦᩱ䛻䛚䛡䜛⇕㟁ኚຠ⋡䛾ᣦᶆ䛸䛧䛶䚸୍⯡ⓗ䛻ᛶ⬟ᣦ ᩘ Z [1/K] 䛜⏝䛔䜙䜜䜛䚹 ܵʹߪ ܼൌ ߢ S䠖༢ ᗘᕪ䛒䛯䜚Ⓨ⏕䛩䜛⇕㉳㟁ຊ(䝊䞊䝧䝑䜽ಀᩘ)[V/K] σ䠖㟁Ẽఏᑟ⋡[1/(Ω䞉m)] κ䠖⇕ఏᑟ⋡[W/(m䞉K)] 䞉Ⰻ Ⰻ䛔⇕㟁ᮦᩱ э䛝䛺Z 䜢ᣢ䛴ᮦᩱ э䛝䛺⇕㉳㟁ຊ䛸㟁Ẽఏᑟ⋡䚸ᑠ䛥䛔⇕ఏᑟ⋡䜢ᣢ䛴ᮦᩱ ⫼ᬒ 3 㟁Ẽఏᑟ⋡䚸⇕㉳㟁ຊ䚸⇕ఏᑟ⋡䛿䜻䝱䝸䜰⃰ᗘ䛾㛵ᩘ䛷䛒䜛䚹 ܵʹߪ 䜻䝱䝸䜰⃰ᗘ䛜ῶᑡ䛩䜛䛸䞉䞉䞉 ܼൌ ߢ 㟁Ẽఏᑟ⋡σ䛸⇕ఏᑟ⋡κ䛿ῶᑡ䛩䜛䛜䚸⇕㉳㟁ຊS䛿ቑຍ䛩䜛䚹 э1019 cm−3⛬ᗘ䛾䜻䝱䝸䜰⃰ᗘ䛷᭱䛾⇕㟁ᛶ⬟ᣦᩘZ䛜ᚓ䜙䜜䜛䚹 Bi2Te3䚸SiGe䚸PbTe䛺䛹䛾䝗䞊䝥༙ᑟయ䛾ᛶ⬟䛿䜻䝱䝸䜰⃰ᗘ䛾ほⅬ䛛䜙ホ౯䛥䜜䜛䚹 [1] G. Mahan et al., Phys. Today 50 (1997) ᅗ ρ䚸S䚸κ䚸Z䛾䜻䝱䝸䜰⃰ᗘ౫Ꮡᛶ ⫼ᬒ 4 •ᒙ ᒙ≧䝁䝞䝹䝖㓟≀NaCoO2 ᐊ 䛷㟁Ẽᢠ䛜200 μΩ cm௨ୗ䛷 䛒䜛䛻䜒㛵䜟䜙䛪䚸⇕㉳㟁ຊ䛿80 μV/K 䜢㉸䛘䜛䚹 㧗䛔⇕㉳㟁ຊ䛸㔠ᒓఏᑟᛶ䜢᭷䛩䜛䚹 㧗 Ᏻᐃᛶ䜢ᣢ䛴䚹 [2] I. Terasaki et al., Phys. Rev. B56 (1997) •Ca3Co4O9䚸Bi2Sr3Co2O9䚸Tl0.4(Sr0.9O)1.12CoO2 NaCoO2䛸ྠ䛨䜘䛖䛻CoO2୕ゅ᱁ Ꮚᒙ䜢ᣢ䛱䚸䛝䛺⇕㉳㟁ຊ䛸㔠 ᒓఏᑟᛶ䜢᭷䛩䜛䚹 Ca3Co4O9䛿⇕ఏᑟ⋡䛜ప䛟䚸ᛶ⬟ ᣦᩘ䛿973 K䛷ZT = 0.87䜢㉸䛘䜛 [9] Y. Miyazaki et al., J. Phys. Soc. Jpn. 71 (2002) ⫼ᬒ 5 ᒙ≧䝁䝞䝹䝖㓟≀䛻䛚䛔䛶䚸䛝䛺⇕㉳㟁ຊ䛻䛴䛺䛜䜛≀⌮ⓗᶵᵓ䛜ㄽⅬ䚹 ᘧ䚸Co㓟≀䛾⇕㉳㟁ຊ z㐣 㐣ཤ䛾◊✲ 䠍䚸ᒙ≧䝁䝞䝹䝖㓟≀䛜♧䛩䛝䛺⇕㉳㟁ຊ 䞉Co3䠇/Co4䠇䛾ඹᏑ g3䠈g4 : Co3+䠈Co4+ 䛾㓄⨨ᩘ x : Co4+䛾⃰ᗘ 䞉Co 3d㌶㐨䛜ᣢ䛴䝇䝢䞁ከ㔜ᗘ䛻䜘䜛䜶䞁䝖䝻䝢䞊 ↓ [10] W. Koshibae et al., ㈇䛾 ᗘಀᩘ䜢䜒䛴㔠ᒓ㟁Ꮚఏᑟᛶ䜢ㄝ᫂䛷䛝䛶䛔䛺䛔䚹 Phys. Rev. B 62 (2000) 䠎䚸ᒙ≧䝁䝞䝹䝖㓟≀䛻䛴䛔䛶㧗ศゎ⬟ARPES䛻䜘䛳 䛶䝁䝠䞊䝺䞁䝖–䜲䞁䝁䝠䞊䝺䞁䝖㑄⛣䛜ほᐹ䛥䜜䜛䚹 ᙉ㟁Ꮚ┦㛵䛻䜘䜚σ䜔S䛺䛹䛾㟁Ꮚ㍺㏦≉ᛶ䛿ᙳ㡪䜢ཷ 䛡䜛䚹 э䝣䜵䝹䝭䝺䝧䝹(EF)㏆ഐ䛾ග㟁Ꮚ䝇䝨䜽䝖䝹䜢⏝䛔䛶 㟁Ꮚ㍺㏦≉ᛶ䜢㆟ㄽ䛩䜛䚹 ᅗ䚸NaCo2O4䛾ARPES [11] T. Valla, D.P. Jhonson et al., Nature 417 (2002) ◊✲┠ⓗ Ca3Co4O9䛾㟁Ꮚᵓ㐀䜢ග㟁Ꮚศග䛸㌾X⥺Ⓨග䛚䜘䜃 ྾ศග䜢䛳䛶ㄪᰝ䚹 э㟁Ꮚ㍺㏦≉ᛶσ䜔S䜢EF㏆ഐ䛻䛚䛡䜛㟁Ꮚᵓ㐀䛾ほⅬ 䛛䜙㆟ㄽ䚹 ᐃ䝇䝨䜽䝖䝹䛛䜙S(T)䜢ィ⟬䚹 эᒙ≧䝁䝞䝹䝖㓟≀䛻䛚䛡䜛䛝䛺⇕㉳㟁ຊ䛾ཎᅉ䜢 ㆟ㄽ䚹 6 ᐇ㦂᮲௳ 7 ヨᩱ䠖 䝣䝷䝑䜽䝇ἲ䛻䜘䜚స〇䛧䛯Ca3Co4O9༢⤖ᬗ RPES ᐃ 䞉ሙᡤ䠖 SPring-8䛾BL25SU 䞉ධᑕග䜶䝛䝹䜼䞊䠖 hν = 775–780 eV 䞉䜶䝛䝹䜼䞊ศゎ⬟䠖 120 meV 䞉䜰䝘䝷䜲䝄䞊䠖 Gammadata-Sicenta SES2002 UPS ᐃ 䞉ሙᡤ䠖 ᮾிᏛ䛾ISSP 䞉䜶䝛䝹䜼䞊ศゎ⬟䠖 10 meV 䞉䜰䝘䝷䜲䝄䞊䠖 Gammadata-Sicenta SES2002 䞉Ύί⾲㠃䠖 10−11 Torr ୗ䛷㛤 XAS ᐃ 䞉ሙᡤ䠖 Photon Factory KEK䛾BL19B 䞉䜰䝘䝷䜲䝄䞊䠖 Shimadzu EPMA1400 ᐇ㦂⤖ᯝ hν = 778.3 eV at 20 K 8 hν = 771 eV at 20K A䠖1.0 eV B䠖2.9 eV C䠖3.5 eV D䠖5.0 eV E䠖 6.2 eV hν = 778.3 eV at 20 K at room temperature (a)Co 2p–3d RPES䝇䝨䜽䝖䝹 (b)XPS䝇䝨䜽䝖䝹 (c)Co 2p–3d ྾䝇䝨䜽䝖䝹 (d)Co 2p–3d䛾Ⓨග䝇䝨䜽䝖䝹 zCo 2p–3dඹ㬆䚹 эD௨እ䛾䝞䞁䝗䛜᫂☜䛻䛺䜛䚹 zCa3Co4O9䛾౯㟁Ꮚᖏ䛿Co 3d 䛸O 2p䛷ᵓᡂ䚹Co 3d䛾せ⣲䜢 ᣢ䛴䝞䞁䝗䛿Co 2p–3dඹ㬆䛷ᙉ 䜑䜙䜜䜛䚹 ↓ Co 2p–3dඹ㬆䛷ᾘ䛘䛯D䛿O 2p 䝞䞁䝗 zXPS䝇䝨䜽䝖䝹୰䛾㗦䛔A䛸䚸 RPES䛚䜘䜃SXES䝇䝨䜽䝖䝹୰䛾 ᑠ䛥䛺A䛿䚸1.0 eV䛷䛾䝞䞁䝗䛜 Co 3d䛰䛡䛷䛺䛟O 2pᡂศ䜒ከ䛟 ྵ䜐䛣䛸䜢♧䛩䚹 ᐇ㦂⤖ᯝ 9 •EF䛿1.0 eV䜢୰ᚰ䛸䛩䜛⊃䛔䝞䞁䝗䛾㧗䜶䝛䝹䜼䞊➃䛻⨨䛩䜛䚹 •EF䛻䛚䛡䜛≧ែᐦᗘ(N(EF))䛿䛛䛺䜚ᑠ䛥䛔䛜᭷㝈䛷䛒䜛䚹 •200K௨ୖ䛾㧗 䛻䛚䛡䜛Ca3Co4O9䛾㟁Ẽᢠ⋡䛿ṇ䛾 ᗘಀ ᩘ䜢ᣢ䛴䚹(ᆺⓗ䛺㔠ᒓⓗᣲື) я100K௨ୗ䜎䛷 ᗘ䛜పୗ䛩䜛䛸䛸䜒䛻㟁Ẽᢠ⋡䛿ᖜ䛻ቑ ຍ䛩䜛 ᐇ㦂⤖ᯝ 10 ධᑕ䜶䝛䝹䜼䞊hν = 778.3 eV ᅗ2䚸(a) XPS䝇䝨䜽䝖䝹 (b) EF㏆ഐ䛾UPS䝇䝨䜽䝖䝹 50 K௨ୖ䛷䚸 N(EF)䛜᭷㝈䛻ಖ䛯䜜䛶䛚䜚䚸㔠ᒓ≧ែ䜢♧䛧䛶䛔䜛䚹 N(EF)䛜 ᗘ䛾పୗ䛸䛸䜒䛻ῶᑡ䚹 20 K䛻䛚䛔䛶䜋䛸䜣䛹ᙉᗘ䛜䛺䛔䚹 ᐇ㦂⤖ᯝ [4] A.C. Masset et al., Phys. Rev. B 62 (2000) 11 [6] R. Funahashi et al., Mat. Trans. 42 (2001) 50 K௨ୗ䛷䛾 ᗘ䛾పୗ䛻క䛖㟁Ẽᢠ⋡䛸䝩䞊䝹ಀᩘ䛾ቑຍ эEF䜢ᶓษ䜛䜶䝛䝹䜼䞊䜼䝱䝑䝥䛾Ⓨ⌧䛻䜘䜛ఏᑟ㟁Ꮚ䛾ᩘ䛾ῶᑡ 50 K௨ୗ䛷䛾㟁Ẽᢠ⋡䛾 ᗘ౫Ꮡᛶ䜢⌮ゎ䛩䜛䛯䜑䛻䚸 䜶䝛䝹䜼䞊䜼䝱䝑䝥䛾 ᗘ౫Ꮡᛶ䜢᫂䜙䛛䛻䛩䜛䛯䜑䛾䛥䜙䛺䜛ᐃ㔞ศᯒ䛜ᚲせ䚹 ᐇ㦂⤖ᯝ EF䜢ᶓษ䜛䜶䝛䝹䜼䞊䜼䝱䝑䝥Ⓨ⌧䛾⌮⏤䛿᫂䜙䛛䛷䛿䛺䛔䚹 •䜼䝱䝑䝥Ⓨ⏕ᶵᵓ䛻ᑐ䛩䜛2䛴䛾⪃䛘 100 K௨ୗ䛷䛾䝇䝢䞁ᐦᗘἼ(SDW)䛾Ⓨ⌧䚹 э䝣䜵䝹䝭㠃䛾䝛䝇䝔䜱䞁䜾䛻䜘䜚䜼䝱䝑䝥Ⓨ⏕? 㟁Ꮚ┦㛵䛻䜘䜛䜒䛾 ᙉ䛔㟁Ꮚ┦㛵䜢ᣢ䛴୕ゅ᱁Ꮚ䛜䝣䜵䝹䝭㠃䛾䝛䝇䝔䜱䞁䜾 䛺䛧䛷䝇䝢䞁ᐦᗘἼ䛸䜼䝱䝑䝥䜢Ⓨ⌧䛩䜛ྍ⬟ᛶ䚹 䛧䛛䛧䚸䝁䝠䞊䝺䞁䝖–䜲䞁䝁䝠䞊䝺䞁䝖㑄⛣䛿㧗ศゎ⬟UPS ᐃ䛻䛚䛔䛶ほᐹ䛥䜜䛺䛛䛳䛯䚹 э䝣䜵䝹䝭㠃䛾䝛䝇䝔䜱䞁䜾䛜Ca3Co4O9䛻䛚䛡䜛 䜼䝱䝑䝥Ⓨ⌧䛾ཎᅉ 12 ⪃ᐹ 13 䝪䝹䝒䝬䞁㍺㏦᪉⛬ᘧ䛻ᇶ䛵䛔䛶ᑟฟ䛥䜜䛯䚸㔠ᒓ⣔䛻䛚䛡䜛⇕㉳㟁ຊS(T) ∂f(ε)/∂ε䛿μ䜢୰ᚰ䛸䛩䜛ᖜᩘkBT䛾䜶䝛䝹䜼䞊 ⠊ᅖ䛻䛚䛔䛶䛾䜏᭷㝈䛾್䜢ᣢ䛴 σ(ε)䠖㟁Ẽఏᑟ⋡䜈䛾㟁Ꮚ䛾ᐤ f(ε)䠖䝣䜵䝹䝭–䝕䜱䝷䝑䜽ศᕸ㛵ᩘ μ䠖Ꮫ䝫䝔䞁䝅䝱䝹 ➼᪉ᛶ䛾⣔䛻䛚䛡䜛σ(ε) ᘧ(1)䛾✚ศ䛷⪃៖䛥䜜䛯䜶䝛䝹䜼䞊⠊ᅖ э∂f(ε)/∂ε䛜᭷㝈್䜢ᣢ䛴䜶䝛䝹䜼䞊⠊ᅖ䛾䛯䜑㠀ᖖ䛻⊃䛔 э䜶䝛䝹䜼䞊౫Ꮡ䛧䛺䛔⩌㏿ᗘ䛚䜘䜃⦆㛫䜢௬ᐃ ⪃ᐹ A(ε)䠖㠃✚ v(ε)䠖⩌㏿ᗘ τ(ε)䠖⦆㛫 N(ε)䠖≧ែᐦᗘ 14 ᘧ(1)䜢ኚᙧ zS(T)䜢᥎ᐃ䛩䜛䛯䜑䛻䚸ᘧ(3)୰䛾N(ε)䛾௦ 䜟䜚䛻UPS䝇䝨䜽䝖䝹䜢⏝䚹 zEF䛾䛩䛠ୖ䛾ఏᑟᖏ䛻䛴䛔䛶䛾ሗ䜢ᚓ 䜛䛯䜑䛻䚸fRT(ε)䛷䛳䛯ᐊ USP䝇䝨䜽䝖䝹 䜢⏝䚹 zS(T)䛾ィ⟬䛷⏝䛩䜛୕䛴䛾䝰䝕䝹䜢ᵓ⠏䚹 ᅗ3䚸ᐊ 䛷 ᐃ䛥䜜䛯Ca3Co4O9䛾UPS䝇䝨䜽䝖䝹䛸 䝣䜵䝹䝭–䝕䜱䝷䝑䜽ศᕸ㛵ᩘ䛷䛳䛯䜒䛾(UPS/FD). ⪃ᐹ 15 [4] A.C. Masset, et al., Phys. Rev. B 62 (2000) [8] M. Shikano, et al., Phys. Lett. 82 (2003) zᐇ㦂್䛸ྠ䛨䜘䛖䛻䝅䝭䝳䝺䞊䝅䝵䞁䛻䛚䛔䛶䜒 S(T)䛜ṇ䛾 ᗘ౫Ꮡᛶ䜢ᣢ䛴䚹 z ᐃ䛥䜜䛯S(T)䛸ィ⟬䛥䜜䛯S(T)䛾㐪䛔 э䜶䝛䝹䜼䞊౫Ꮡ䛧䛺䛔⩌㏿ᗘ䛸⦆㛫䛾௬ᐃ ᅗ4䚸UPS䝇䝨䜽䝖䝹䛛䜙ィ⟬䛥䜜䛯 S(T)䛸㐣ཤ䛾◊✲䛻䜘䜛S(T). Ca3Co4O9䛻㛵䛧䛶ほ 䛥䜜䛯䛝䛺䝊䞊䝧䝑䜽ಀᩘ ⊃䛔䝞䞁䝗ᖜ䛸䛭䛾䝞䞁䝗➃㏆䛾EF䛻䜘䛳䛶≉ᚩ䛵䛡䜙䜜䜛㟁Ꮚᵓ㐀䛜 㛵ಀ 䜎䛸䜑 16 zCa3Co4O9䛻䛚䛡䜛౯㟁Ꮚᖏ䛾㟁Ꮚᵓ㐀䛜䚸RPES ᐃ䛸 UPS ᐃ䜢⤌䜏ྜ䜟䛫䜛䛣䛸䛻䜘䛳䛶Ỵᐃ䛥䜜䛯䚹 zEF㏆ഐ䛾㟁Ꮚᵓ㐀䛾≉ᚩ 䞉2 eV䜘䜚ᑠ䛥䛔ᖜ䛾⊃䛔䝞䞁䝗 䞉⊃䛔䝞䞁䝗䛾㧗䜶䝛䝹䜼䞊➃㏆䛻䛒䜛EF zUPS䝇䝨䜽䝖䝹䛛䜙ィ⟬䛥䜜䛯S(T)䛻䜘䛳䛶Ca3Co4O9䛾㟁 Ꮚᵓ㐀䛸㔠ᒓⓗ㟁Ꮚ㍺㏦䛜䚸䛝䛺⇕㉳㟁ຊ䛸ప䛔㟁Ẽ ᢠ⋡䛾୧❧䛻㛵ಀ䛩䜛䛣䛸䛜䜟䛛䛳䛯䚹
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