Title Page

Abstract

Contents

Chapter 1. Introduction 10

1.1. Overview about perovskite structure 10

1.2. Progression of study about Ca₂RuO₄ 12

1.3. Features of Ca₂RuO₄ 15

1.4. Magnon and Higgs mode 17

Chapter 2. Sample and Method 20

Chapter 3. Result 25

3.1. Incident beam angle resolved Raman spectrum result 25

3.2. Temperature dependent Raman spectrum result 30

3.3. Difference between 532 nm and 660 nm at excitation laser 34

Chapter 4. Discussion 38

4.1. Temperature dependent phonon evolution 38

4.2. Anti-symmetry Raman tensor 41

4.3. Magnon asymmetry from excitation energy 43

4.4. B1g composite excitation anisotropy[이미지참조] 46

Chapter 5. Conclusion 48

References 50

국문초록 52

Table 1. Center position of peaks and comparison to reference data at parallel polarization. 36

Table 2. Center position of peaks and comparison to reference data at cross polarization. 37

Figure 1.1. Schematic image of the Ca₂RuO₄ crystal structure. 11

Figure 1.2.1. Structural study about Ca₂RuO₄. 13

Figure 1.2.2. Higgs continuum with magnon and new magnetic phase called as spin-glass(SG) depends on element. 14

Figure 1.3. Energy level split by crystal structure and orbital. 16

Figure 1.4.1. Schematic magnon generation by 1 spin inversion excitation and spin arrangement of anti-ferromagnetism. 18

Figure 1.4.2. Higgs mode continuum and magnon from Raman result of Ca₂RuO₄ at parallel and cross polarization. 19

Figure 2.1. Sample image with 1x, 10x, and 40x. 22

Figure 2.2. Dependent variables of the experiment. 23

Figure 2.3. Angle, temperature-resolvable Raman spectroscopy system 24

Figure 3.1.1. Angle of incident and scattered light. Incident beam angle dependence Raman spectroscopy result with contour plot. 27

Figure 3.1.2. Incident beam angle dependence Raman spectroscopy result with fitted intensity-sine fitting polar-plot at parallel polarization. 28

Figure 3.1.3. Incident beam angle dependence Raman spectroscopy result with fitted intensity-sine fitting polar-plot at cross polarization. 29

Figure 3.2.1. Temperature dependent Raman spectroscopy result at parallel polarization. 32

Figure 3.2.2. Temperature dependent Raman spectroscopy result at cross polarization. 33

Figure 3.3. Intensity of magnon difference between laser wavelength 532 nm and 660 nm 35

Figure 4.1.1. Peak position of Ag1 and relative lattice constant of Ca₂RuO₄.[이미지참조] 39

Figure 4.1.2. Asymmetry of Ag7 with error bar and amplitude mode of Ca₂RuO₄.[이미지참조] 40

Figure 4.3.1. Polar-plotted magnon at laser 532 nm and 660 nm and calculated ruthenium's 4d orbital transition from dyz/zx to dyz/zx.[이미지참조] 44

Figure 4.3.2. Polar-plotted magnon at laser 532 nm, 561 nm, 660 nm and asymmetry ratio. 45

Figure 4.4. Polar-plotted integral result of B1g composite excitation at laser 532 nm, 660 nm.[이미지참조] 47

Figure 5.1. Expectation about asymmetry ratio with blue laser which not occur resonant Raman. 49