{"created":"2023-06-20T13:20:17.064649+00:00","id":289,"links":{},"metadata":{"_buckets":{"deposit":"35ba3d2e-df50-496b-b5d5-f2410d612b35"},"_deposit":{"created_by":1,"id":"289","owners":[1],"pid":{"revision_id":0,"type":"depid","value":"289"},"status":"published"},"_oai":{"id":"oai:ir.soken.ac.jp:00000289","sets":["2:427:10"]},"author_link":["8008","8007","8009"],"item_1_creator_2":{"attribute_name":"著者名","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"谷口, 弘三"}],"nameIdentifiers":[{}]}]},"item_1_creator_3":{"attribute_name":"フリガナ","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"タニグチ, ヒロミ"}],"nameIdentifiers":[{}]}]},"item_1_date_granted_11":{"attribute_name":"学位授与年月日","attribute_value_mlt":[{"subitem_dategranted":"1997-03-24"}]},"item_1_degree_grantor_5":{"attribute_name":"学位授与機関","attribute_value_mlt":[{"subitem_degreegrantor":[{"subitem_degreegrantor_name":"総合研究大学院大学"}]}]},"item_1_degree_name_6":{"attribute_name":"学位名","attribute_value_mlt":[{"subitem_degreename":"博士（理学）"}]},"item_1_description_12":{"attribute_name":"要旨","attribute_value_mlt":[{"subitem_description":"In the high-Tc cuprate superconductors, which have unusual superconducting parameters, the vortices largely fluctuate and are not permitted to form the Abrikosov lattice in higher field (H) and temperature (T) region in H-T plane.  The first-order phase transition corresponding to the vortex lattice melting was observed in resistive, magnetic and thermodynamic measurements.  In the BEDT-TTF (ET) molecule-based organic superconductors, the large London penetration depth due to low carrier density and the high anisotropy due to layered crystal structure are considered to enhance the fluctuations of the vortices like the cuprate superconductors.  There are many ingredients which affect the vortex state such as pinning mechanism, anisotropy parameter and coherence length.  These parameters span different ranges of values between organics and high-Tc cuprates.  Therefore, study of the vortex state in the organic systems leads to comprehensive understanding of the quasi-two-dimensional vortex system.  The purpose of this thesis is clarifying the vortex state of the quasi-two-dimensional ET-based superconductor, α-(BEDT-TTF)2NH4Hg(SCN)4(α-ET), which has a layered structure with thick anion layer.  This structural characteristics is expected to give high anisotropy in the superconductivity in this material.  This is the reason why this salt was chosen in the present study.  The superconductivity in a zero field and the vortex state under magnetic fields perpendicular to the conducting plane were investigated by means of resistive and inductive measurements.\n  The α-ET salt is known as an organic conductor which shows superconductivity around 1K.  First of all, the normal state property was investigated through the resistive measurements.  One of the most important results is that the anisotropy of the normal state conductivity, σ// /σ⊥, amounts to 10 5～10 6.  This value is lager than any other organic superconductor's.  It is noted that the anisotropy of κ-ET (κ-(BEDT-TTF)2Cu(NCS)2), which can be viewed as a Josephson-coupled system through several experiments, is about l0 3.  Therefore, the enhanced two-dimensional character is expected to manifest itself in the superconducting state in the present material.\n  In order to characterize the superconducting state of this material, electrical resistance and ac susceptibility, χ=χ'- iχ'', were measured in a zero-field condition attained by double μ-metal shields (a residual field was 1mOe or lower).  Gradual decrease of in-plane resistance (I  Conducting plane) and the very small diamagnetic signal of in-plane ac-susceptibility (hac⊥// conducting plane) due to superconductivity appear around 2.3K.  The in-plane diamagnetic signal increases rapidly around 0.9K, where in-plane resistance vanishes asymptotically, and reaches nearly the perfect Meissner value at O.8K.  The bulk transition temperature is considered to be about O.95K, which is consistent with specific heat jump.  These results imply that a quasi-superconducting state exists above 0.95K.  This phenomenon is reminiscent to the Kosterlitz-Thouless behavior, which also shows nonlinerity in the I-V characteristics as was observed in some samples but with less reproducibility.\n  On the other hand, in the out-of-plane configuration (hac conducting plane), χ' starts to appear at 0.95K but reaches only 20 percent of a full Meissner value even at 0.4K.  This fact indicates that out-of-plane penetration depth, λ, is comparable to the sample size.  Assuming an exponential penetration of field into the sample, λ can be calculated from χ', a value of 1.4mm at OK was obtained.  If λ is of the same order of the sample size, the value of χ' should strongly depend on the crystal size.  Then χ' of five crystals with different dimension was examined.  It is confirmed that all the results were explained fairly well by the same value of λ.  Because λ reflects the strength of out-of-plane coupling of superconductivity, such a large λ value means a very weak out-of-plane coupling.  Assuming the in-plane value of penetration depth estimated from the carrier density, anisotropy of penetration depth turns out to be in a rang of 1800-8000, which is consistent with the anisotropy of resistivity because of the relation of λ/λ = (σ// /σ⊥)1/2.  Thus, all these results indicate that this material is the most highly anisotropic quasi-two-dimensional organic superconductor, which can be modeled as a weakly Josephson-coupled system.\n  Such a two-dimensional superconductor is expected to have complicated H-T phase diagram, which is discussed extensively in the BSCCO (Bi2Sr22CaCu2O8+δ).  In the latter part of the present work, the vortex state in this compound in dc fields perpendicular to the layers was studied.  It should be emphasized that, because of the huge anisotropy of the superconductivity, the Josephson length, λ//, becomes comparable or larger than in-plane penetration depth, γs, at low temperatures for the present material, where γ is the anisotropy parameter and s is the interlayer spacing.  The coupling energy of the pancake vortices consist of the Josephson contribution and the electromagnetic one, of which the typical energy scales are φ/γ2 s2 and φ/λ//2, respectively, with φ, the flux quantum.  In this sense, the electromagnetic coupling plays an important role in the out-of-plane correlation of pancake vortices in α-ET, while the correlation of vortices in BSCCO and κ-ET is dominated by the Josephson coupling.  This feature distinguishes the present system from other systems and therefore may affect the vortex state, giving a new H-T phase diagram.\n  From measurements of specific heat in dc fields, the mean-field Hc2 line was determined.  It was found that Ginzburg-Landau coherence length is  500 Å which is one order of magnitude larger than those of BSCCO and κ-ET.  The measurements of in- and out-of-plane ac susceptibility in fields gave a characteristic boundary, which characterizes drastic change in vortex mobility signed by a sharp onset of ac-χ, far below Hc2 line in the H-T plane.   This result suggests that the vortex liquid state exists in a wide field and temperature range below Hc2 line.  Interestingly, the out-of-plane resistivity is found to vanish at a well-defined region in between the two lines.  This is interpreted to reflect progressive growth of the out-of-plane correlation in the mobile vortices.  If the onset of the inductive transition corresponds to the vortex lattice melting and the vanishing of out-of-plane resistibility means dimensional crossover of pancake vortices, these lines can be well explained by the recent Blatter's theory taking account of the electromagnetic coupling within the reasonable values of superconducting parameters.\n  In summary, the superconductivity of the layered organic super-conductor, α-(BEDT-TTF)2NH4Hg(SCN)4, was investigated by the resistive and inductive measurements.  It is uncovered that this system is the quasi-two-dimensional superconductor with the highest anisotropy among the organic systems.  Through the measurements in dc fields, the three characteristic lines were found in the H-T plane.  The first one is the Hc2 line.  The second one is the line which characterizes drastic change of vortex mobility.  And the third is the line indicating the rapid growth of the out-of-plane correlation, suggestive of the dimensional crossover of the mobile pancake vortices.","subitem_description_type":"Other"}]},"item_1_description_18":{"attribute_name":"フォーマット","attribute_value_mlt":[{"subitem_description":"application/pdf","subitem_description_type":"Other"}]},"item_1_description_7":{"attribute_name":"学位記番号","attribute_value_mlt":[{"subitem_description":"総研大甲第259号","subitem_description_type":"Other"}]},"item_1_select_14":{"attribute_name":"所蔵","attribute_value_mlt":[{"subitem_select_item":"有"}]},"item_1_select_8":{"attribute_name":"研究科","attribute_value_mlt":[{"subitem_select_item":"数物科学研究科"}]},"item_1_select_9":{"attribute_name":"専攻","attribute_value_mlt":[{"subitem_select_item":"08 機能分子科学専攻"}]},"item_1_text_10":{"attribute_name":"学位授与年度","attribute_value_mlt":[{"subitem_text_value":"1996"}]},"item_1_version_type_23":{"attribute_name":"著者版フラグ","attribute_value_mlt":[{"subitem_version_resource":"http://purl.org/coar/version/c_ab4af688f83e57aa","subitem_version_type":"AM"}]},"item_creator":{"attribute_name":"著者","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"TANIGUCHI, Hiromi","creatorNameLang":"en"}],"nameIdentifiers":[{}]}]},"item_files":{"attribute_name":"ファイル情報","attribute_type":"file","attribute_value_mlt":[{"accessrole":"open_date","date":[{"dateType":"Available","dateValue":"2016-02-17"}],"displaytype":"simple","filename":"甲259_要旨.pdf","filesize":[{"value":"380.6 kB"}],"format":"application/pdf","licensetype":"license_11","mimetype":"application/pdf","url":{"label":"要旨・審査要旨 / Abstract, Screening Result","url":"https://ir.soken.ac.jp/record/289/files/甲259_要旨.pdf"},"version_id":"4e3f032c-2461-4467-988f-2f869e84c1f3"},{"accessrole":"open_date","date":[{"dateType":"Available","dateValue":"2016-02-17"}],"displaytype":"simple","filename":"甲259_本文.pdf","filesize":[{"value":"6.6 MB"}],"format":"application/pdf","licensetype":"license_11","mimetype":"application/pdf","url":{"label":"本文 / Thesis","url":"https://ir.soken.ac.jp/record/289/files/甲259_本文.pdf"},"version_id":"280e538e-321e-4421-9259-18f04e5f4737"}]},"item_language":{"attribute_name":"言語","attribute_value_mlt":[{"subitem_language":"eng"}]},"item_resource_type":{"attribute_name":"資源タイプ","attribute_value_mlt":[{"resourcetype":"thesis","resourceuri":"http://purl.org/coar/resource_type/c_46ec"}]},"item_title":"Anisotropy and vortex state in the quasi-two-dimensional superconductor, α-(BEDT-TTF)2NH4Hg(SCN)4","item_titles":{"attribute_name":"タイトル","attribute_value_mlt":[{"subitem_title":"Anisotropy and vortex state in the quasi-two-dimensional superconductor, α-(BEDT-TTF)2NH4Hg(SCN)4"},{"subitem_title":"Anisotropy and vortex state in the quasi-two-dimensional superconductor, α-(BEDT-TTF)2NH4Hg(SCN)4","subitem_title_language":"en"}]},"item_type_id":"1","owner":"1","path":["10"],"pubdate":{"attribute_name":"公開日","attribute_value":"2010-02-22"},"publish_date":"2010-02-22","publish_status":"0","recid":"289","relation_version_is_last":true,"title":["Anisotropy and vortex state in the quasi-two-dimensional superconductor, α-(BEDT-TTF)2NH4Hg(SCN)4"],"weko_creator_id":"1","weko_shared_id":1},"updated":"2023-06-20T14:57:36.741543+00:00"}