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The lattice structure of theorganic conductors (TMTSF)2X is constructed by a stacking of weakly dimerizedTMTSF molecules. Therefore, the band structure is quasi-one-dimensional, andthe Fermi surface is open (disconnected) in the b-axis direction.Some important experiments regarding the pairing symmetry is as follows. Thenuclear spin relaxation rate 1/T1 measurements have suggested anisotropic superconductinggap function, and the upper critical field Hc2 measurements haveshown large Hc2 exceeding the Pauli paramagnetic limit HP. Recent Knight shiftmeasurement and the upper critical field measurement show that two or three superconductingstates arise upon applying the magnetic field across near HP. Theseresults indicate, in the large field regime, the possibility of a spin triplet paringstate or an FFLO (Fulde-Ferrell-Larkin-Ovchinnikov) state in which the Cooperpairs have finite total momentum. As for the spin-density-wave (SDW) phasein the vicinity of the superconducting phase in (TMTSF)2PF6, a coexistence of2kF -SDW and 2kF -charge-density-wave (CDW) has been observed.Previous theoretical studies have shown that gap functions having nodes intersectingthe Fermi surface, e.g. spin singlet d-wave or triplet f-wave, are consistentwith the NMR 1/T1 measurements. Some of the microscopic theories have shownthat the distant electron-electron interactions make the triplet f-wave pairing competitiveagainst the singlet d-wave pairing.On the basis of the above backgrounds, the following subjects are studied onthe extended Hubbard model for (TMTSF)2X.(1), Effect of the magnetic field on the pairing competition.(2), Pairing competition and the competition between the superconductivity anddensity-waves in a realistic model.(3), Non-magnetic impurity effect on the pairing competition.Subjects (1) and (2) are studied microscopically, while subject (3) is treated bya phenomenological technique. The main conclusions are the following. (1) Thetriplet pairing mediated by the 2kF -spin and 2kF -charge fluctuations is stronglyenhanced by applying the magnetic field. Moreover, a consecutive pairing transitionfrom singlet pairing to FFLO and further to triplet pairing can take placeupon increasing the magnetic field, where singlet and triplet pairing componentsmix strongly in the FFLO state. (2) The singlet d-wave pairing, as compared tothe triplet f-wave pairing, is suppressed within the realistic parameter regime.Also, increasing the dimerization has no effect on the pairing competition, but enhancesthe density-wave state. 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擬一次元有機導体における超伝導対称性に関する理論的研究
https://uec.repo.nii.ac.jp/records/1140
https://uec.repo.nii.ac.jp/records/114016aacc06-a43e-4f35-a14b-24a5254c89c0
名前 / ファイル | ライセンス | アクション |
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9000000340.pdf (17.3 MB)
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Item type | 学位論文 / Thesis or Dissertation(1) | |||||
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公開日 | 2009-03-24 | |||||
タイトル | ||||||
言語 | ja | |||||
タイトル | 擬一次元有機導体における超伝導対称性に関する理論的研究 | |||||
タイトル | ||||||
言語 | en | |||||
タイトル | Theoretical study on the pairing symmetry in quasi-one-dimensional organic superconductors | |||||
言語 | ||||||
言語 | jpn | |||||
資源タイプ | ||||||
資源タイプ識別子 | http://purl.org/coar/resource_type/c_46ec | |||||
資源タイプ | thesis | |||||
著者 |
相澤, 啓仁
× 相澤, 啓仁 |
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抄録 | ||||||
内容記述タイプ | Abstract | |||||
内容記述 | In the present thesis, the competition among different pairing symmetries orstates is studied on a model for organic superconductors (TMTSF)2X (TMTSF=tetramethyl-tetraselena fulvalene, X=PF6, ClO4 etc.). The lattice structure of theorganic conductors (TMTSF)2X is constructed by a stacking of weakly dimerizedTMTSF molecules. Therefore, the band structure is quasi-one-dimensional, andthe Fermi surface is open (disconnected) in the b-axis direction.Some important experiments regarding the pairing symmetry is as follows. Thenuclear spin relaxation rate 1/T1 measurements have suggested anisotropic superconductinggap function, and the upper critical field Hc2 measurements haveshown large Hc2 exceeding the Pauli paramagnetic limit HP. Recent Knight shiftmeasurement and the upper critical field measurement show that two or three superconductingstates arise upon applying the magnetic field across near HP. Theseresults indicate, in the large field regime, the possibility of a spin triplet paringstate or an FFLO (Fulde-Ferrell-Larkin-Ovchinnikov) state in which the Cooperpairs have finite total momentum. As for the spin-density-wave (SDW) phasein the vicinity of the superconducting phase in (TMTSF)2PF6, a coexistence of2kF -SDW and 2kF -charge-density-wave (CDW) has been observed.Previous theoretical studies have shown that gap functions having nodes intersectingthe Fermi surface, e.g. spin singlet d-wave or triplet f-wave, are consistentwith the NMR 1/T1 measurements. Some of the microscopic theories have shownthat the distant electron-electron interactions make the triplet f-wave pairing competitiveagainst the singlet d-wave pairing.On the basis of the above backgrounds, the following subjects are studied onthe extended Hubbard model for (TMTSF)2X.(1), Effect of the magnetic field on the pairing competition.(2), Pairing competition and the competition between the superconductivity anddensity-waves in a realistic model.(3), Non-magnetic impurity effect on the pairing competition.Subjects (1) and (2) are studied microscopically, while subject (3) is treated bya phenomenological technique. The main conclusions are the following. (1) Thetriplet pairing mediated by the 2kF -spin and 2kF -charge fluctuations is stronglyenhanced by applying the magnetic field. Moreover, a consecutive pairing transitionfrom singlet pairing to FFLO and further to triplet pairing can take placeupon increasing the magnetic field, where singlet and triplet pairing componentsmix strongly in the FFLO state. (2) The singlet d-wave pairing, as compared tothe triplet f-wave pairing, is suppressed within the realistic parameter regime.Also, increasing the dimerization has no effect on the pairing competition, but enhancesthe density-wave state. (3) When the effect of the non-magnetic impuritiesis taken into account by an anisotropic impurity scattering potential, the tripletf-wave pairing is more strongly suppressed than the singlet d-wave pairing. | |||||
学位名 | ||||||
学位名 | 博士(理学) | |||||
学位授与機関 | ||||||
学位授与機関名 | 電気通信大学 | |||||
学位授与年度 | ||||||
内容記述タイプ | Other | |||||
内容記述 | 2008 | |||||
学位授与年月日 | ||||||
学位授与年月日 | 2009-03-24 |