37 research outputs found
SI-STM Study on Novel Fe Based Superconductor Ca0.9La0.1FeAs2
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Όλ¬Έ (λ°μ¬) -- μμΈλνκ΅ λνμ : μμ°κ³Όνλν 물리·μ²λ¬ΈνλΆ(물리νμ 곡), 2020. 8. μ΄μ§νΈ.After the discovery of the first Fe-based superconductor in 2006, several different types of Fe-based superconductors are synthesized and theoretical and experimental efforts were devoted to understand the mechanism of superconductivity. Ca0.9La0.1FeAs2 was first synthesized in 2013 and attracted attentions of many theoretical researchers due to its unique As zigzag chain layer which can induce a topological superconductor. To elucidate the existence of topologically non-trivial property in this material, spectroscopic study is urgent. While Angle-Resolved PhotoEmission Spectroscopy (ARPES) results on Ca0.9La0.1FeAs2 were reported, there is no Scanning Tunneling Microscope (STM) result so far.
In this thesis, the first STM result on Ca0.9La0.1FeAs2 will be discussed in detail. All four types of different terminating layer were identified by analyzing topographic images, differential conductance maps, as well as spectral features. Each terminating layer exhibits a distinctive spectroscopic character. A nematic feature was observed on FeAs layer which has dxz and dyz orbital character. Ca layer above As zigzag chain layer shows an inhomogeneity in gap distribution and conductance map revealed an influence from La dopants on the underlying Ca layer. Cross-correlation analysis seems to suggest that the local superconductivity is disturbed by La dopants. Ca terminating layer above FeAs layer contained many crevices through which we could directly access the FeAs layer revealing a clear gap with coherence peaks. On As zigzag chain layer, our Fourier analysis revealed a Dirac-cone dispersion which is compatible with the previous ARPES results. Remarkably, many zero bias conductance peaks were observed on As zigzag chain layer especially only on top of the crevices of underlying Ca layer. The existence of zero bias conductance peak on As chain layer might provide a clue to verifying if Ca0.9La0.1FeAs2 is topologically non-trivial superconductor. We hope our study opens a gate to a new direction in the study of this fascinating material.μ΅μ΄μ μ² κΈ°λ° μ΄μ λμ²΄κ° 2006λ
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μ μ² κΈ°λ° μ΄μ λμ²΄κ° μ¬λΏ λ°κ²¬λμμΌλ©°, μ΄μ λ λ©μ»€λμ¦μ μ΄ν΄νκΈ° μν΄ κ·Έκ²λ€μ λν λ§μ μ΄λ‘ μ κ³μ° λ° μ€νμ΄ μ§νλμλ€. Ca0.9La0.1FeAs2 λ 2013λ
μ λ°κ²¬λ λ¬Όμ§λ‘ κ³ μ ν As μ§κ·Έμ¬κ·Έ μΈ΅κ³Ό μμ μ΄μ λ체μ κ°λ₯μ± λλ¬Έμ μ€νμ μ΄λ‘ μ μΈ κ΄μ¬μ λμλ€. κ·ΈλΌμλ λΆκ΅¬νκ³ μμ§ μ£Όμ¬ν ν°λλ§ νλ―Έκ²½ (STM)μ μ΄μ©ν κ²°κ³Όλ λ³΄κ³ λμ§ μμλ€.
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Όλ¬Έμμ Ca0.9La0.1FeAs2 μλ£μ λν μ΅μ΄μ STM κ²°κ³Όλ₯Ό 보μλ€. κ°λ₯ν 4κ°μ νλ©΄λ€μ΄ λͺ¨λ κ΄μΈ‘λμμΌλ©° κ°κ°μ μ§ν μ΄λ―Έμ§, μ λμ¨ λ§΅, μ λμ¨ μ€ννΈλΌμ μ΄μ©νμ¬ νμΈνκ³ κ° νλ©΄μ κ³ μ ν μ±μ§λ€μ λν΄ μ°κ΅¬νμλ€. FeAs μΈ΅μμ λ€λ§ν±ν λͺ¨μ΅μ΄ κ΄μΈ‘λμμΌλ©° κ·Έκ²λ€μ΄ dxz, dyz κΆ€λ μν μ±μ§μ κ°κ³ μμμ 보μλ€. As μ§κ·Έμ¬κ·Έ μ²΄μΈ μΈ΅ μμ μλ μΉΌμ λ μ΄μ΄λ λΉκ· μ§ν κ°μ λΆν¬λ₯Ό 보μμΌλ©°, μ λμ¨ λ§΅μ μλμ Ca μΈ΅μ μλ La λννΈλ€μ 보μ¬μ£Όμλ€. λν μκ΄κ΄κ³ λΆμμ ν΅ν΄ La λννΈκ° κ΅μμ μΌλ‘ μ΄μ λ νμμ μ½νμν€λ κ²μ νμΈνμλ€. FeAs μΈ΅ μμ μλ Ca μΈ΅μ νλ©΄μ μλ νμ ν΅νμ¬ νλ©΄ μ¬κ΅¬μ±μ΄ μΌμ΄λμ§ μμ FeAs μΈ΅μ μ§μ κ΄μΈ‘ν μ μλ κ°λ₯μ±μ 보μ¬μ£Όμλ€. As μ§κ·Έμ¬κ·Έ μ²΄μΈ μΈ΅μμλ νΈλ¦¬μ λ³νμ μ΄μ©νμ¬ Dirac μ½ λΆμ°μ 보μλλ° κ·Έκ²μ μ΄ μΈ΅μ κ³ μ ν μ±μ§μ΄λ€. μ λ‘λ°μ΄μ΄μ€ μ λμ¨ λ΄μ°λ¦¬κ° FeAs μΈ΅ μμ μλ Ca μΈ΅μ ν μμ μλ As μ§κ·Έμ¬κ·Έ μ²΄μΈ μΈ΅ μμ κ΄μΈ‘μ΄ λμλ€. μμ μ μ°μ²΄μ μ΄μ λ κ·Όμ ν¨κ³Όκ° μμμ μ°μ²΄μ μ μ© λ κ°λ₯μ± μΈμ λ€λ₯Έ μλ κ°λ₯μ±λ€μ μ κ±° λμλ€. μ λ‘ λ°μ΄μ΄μ€ μ λμ¨ λ΄μ°λ¦¬λ μ΄ μλ£μμ μ΄λ ν μ€νμ λ ν΄μΌνλμ§ λ°©ν₯μ μ μνλ€.Chapter 1. Introduction on Scanning Tunneling Microscope 1
1.1 Tunneling current and differential conductance 1
1.2 Topographic image 4
1.3 I-V spectrum, differential conductance spectrum and Spectroscopic Imaging Scanning Tunneling Microscopy 5
1.4 Work function measurement and work function map 6
1.5 Systems and equipment in Seoul National University. 6
1.5.1 Electronics 6
1.5.2 The cryostat and the Dewar 8
1.5.3 Sample cleaving stage 8
1.5.4 STM haed with tip treatment stage 10
1.5.5 Ultra low vibration system 12
Chapter 2. Introduction of Superconductivity and Ca0.9La0.1FeAs2 15
2.1 Brief history of superconductor 15
2.2 Fe-Based superconductors 17
2.3 Ca0.9La0.1FeAs2 21
Chapter 3. Nematic feautres on FeAs layer 25
3.1 Identification of FeAs layer 25
3.2. Nematic features observed on FeAs layer. 29
3.3 Summary 34
Chapter 4. Inhomogenous gap distribution and underlying La dopants on Ca/La layer abofe As chain layer 35
4.1 Identification of Ca/La layer above As chain layer 36
4.2 Inhomogeneous gap distribution of Ca-1 layer. 39
4.3. La dopants on underlying layer 43
4.4 Summary 47
Chapter 5. Superconductivity through crevices of Ca/La layer above FeAs layer 49
Chapter 6. Dirac cone dispersion and zero bias conductance peak on As chain layer 55
6.1 Identification of As zigzag chain layer. 56
6.2. Observation of Dirac cone like dispersion 57
6.3. Observation of zero bias conductance peaks 61
6.4. Summary 69
Chapter 7. Conclusion 71
Bibliography 73
Abstract in Korean 77Docto
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κΈ°μ‘΄ κΈ°λ²κ³Όμ λΉκ΅λ₯Ό ν΅νμ¬ μ μν κΈ°λ²μ΄ κ±°λ¦¬κΈ°λ° ν보ꡰ μ μ μ ν΅ν΄ μ¬μΈ΅μ κ²½λ§μ νμ΅μ±λ₯μ κ°μ ν¨μΌλ‘μ¨ μ λ’°μ± μλ μ΅μ ν΄λ₯Ό λμΆν¨μ νμΈνμλ€. μ μν κΈ°λ²μ λ€μμ μμ°μ μ΄ μ‘΄μ¬νλ μ λ₯μΈ΅μμλ μ λ’°λ λμ μμ°λ μμΈ‘μ΄ κ°λ₯νλ―λ‘ μ λ₯μΈ΅ κ°λ°μ μν μμ¬κ²°μ μ λꡬλ‘μ νμ©λ μ μλ€.1. μλ‘ 1
2. μ΄λ‘ μ λ°°κ²½ 7
2.1 κ±°λ¦¬κΈ°λ° κ΅°μ§ν 7
2.2 μ¬μΈ΅μ κ²½λ§ 12
3. μ°κ΅¬ λ°©λ² 17
3.1 μ¬μΈ΅μ κ²½λ§ κ΅¬μ± 20
3.2 κ±°λ¦¬κΈ°λ° ν보ꡰμ ν΅ν νμ΅μ±λ₯ κ°μ 26
4. κ°λ°κΈ°λ²μ κ²μ¦ λ° λΉκ΅λΆμ λ°©λ² 30
4.1 λ€λͺ©μ νμ€ν λ¦¬λ§€μΉ μ±λ₯λΆμ 31
4.2 νμ₯ μ μ©μ± νκ° 77
5. κ²°λ‘ 98
μ°Έκ³ λ¬Έν 101
Appendices 108
Abstract 118Docto
Analysis of drought transcriptome and functional study of CaLEA2, a water stress responsive gene, in hot pepper (capsicum annuum L.)
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Όλ¬Έ(λ°μ¬) --μμΈλνκ΅ λνμ :μλͺ
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A Study on the behavioral characteristics of skier and ski participation models in Korea
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Όλ¬Έ(λ°μ¬)--μμΈλνκ΅ λνμ :μ°λ¦Όμμνκ³Ό,1998.Docto
Process of Using BIM for Small-Scale Construction Projects - Focusing on the Steel-frame Work -
The current study focused on the utilization of building information modeling (BIM) data in steel-frame structures, which help to reduce project durations because they employ prefabricated structural members that are assembled on-site. In addition, a business process model was proposed using BIM data collected during the preconstruction, structural steel fabrication, and on-site construction phases of an actual steel-frame project. The ultimate expectation is that BIM data support at each phase, as well as the increased understanding among project participants, will result in an increase in project management productivity. The results from the current study are summarized as follows: To implement a BIM capable of application to steel-frame projects and data utilization, existing theories were studied to develop the construction project steps, both generally into the preconstruction (A1), steel fabrication (A2), and on-site construction phases, (A3) and specifically into 19 BIM-applicable phases. Based on the derived BIM-applicable phases, the model elements of the BIM object were identified, and the shortcomings of existing steel-frame projects were ameliorated, resulting in an improved data flow model. Moreover, for the proposed BIM data flow to progress efficiently, the BIM specialist needs to be well-acquainted with the phase-specific three-dimensional (3D) model output, and the infrastructure to construct an error-free 3D model must be provided. Based on the actual construction example, the BIM data utilized steel-frame projects — via production reports, clash checks, two-dimensional (2D) drawings, four-dimensional (4D) simulations, and 3D scanning — to make cooperation and communication among participants easier
ζ°ι‘1εθ¨ͺεθηεΆμ ιν η‘η©Ά
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Όλ¬Έ(μμ¬)--μμΈλνκ΅ νμ λνμ :νμ νκ³Ό νμ νμ 곡,1999.Maste
Inducible nitric oxide synthase expression in gastroduodenal diseases infected with helicobacter pylori
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Όλ¬Έ(λ°μ¬)--μμΈλνκ΅ :μνκ³Ό λ΄κ³Όν μ 곡,1999.Docto