鈣鈦礦氧化物(SmBaMn2O6)與異質結構(Nd0.35Sr0.65MnO3/YBa2Cu3O7)的光譜性質研究

Optical studies of perovskite oxides (SmBaMn2O6) and heterostructures (Nd0.35Sr0.65MnO3/YBa2Cu3O7)

廖鈺汝(Liao Yu-Ju)

指導教授 ： 劉祥麟

國立臺灣師範大學/理學院/物理學系/碩士(2017年)

https://doi.org/10.6345/NTNU202202012

摘要

我們研究鈣鈦礦結構Nd0.35Sr0.65MnO3(NSMO)(30 nm)薄膜、YBa2Cu3O7(YBCO)(40 nm)薄膜、NSMO(30 nm)/YBCO(30 nm)異質結構薄膜材料及雙鈣鈦礦結構SmBaMn2O6單晶之光譜性質。我們使用橢圓偏振光譜探究異質結構薄膜材料與SmBaMn2O6單晶的光學常數與電子傳輸性質，並進一步使用拉曼散射光譜探討SmBaMn2O6單晶的晶格-電荷-自旋多重耦合效應。
　　NSMO的室溫光學電導率能譜展現兩個主要的吸收峰，位置分別為1.1 eV和3.7 eV。1.1 eV和3.7 eV分別對應到Mn3+ d→鄰近Mn4+ d及O 2p→Mn 3d軌域之電子躍遷。YBCO的室溫光學電導率能譜譜，有三個主要的吸收峰，分別為3.1 eV、3.8 eV和4.6 eV，3.1 eV對應到O 2p→Cu 3d軌域的電子躍遷，3.8和4.6 eV兩個峰主要為Cu(1) 3d_(3z^2-r^2 )→ 4p_x的電子躍遷。NSMO/YBCO異質結構的吸收峰位置與強度不同於NSMO與YBCO單層薄膜，可能與薄膜應變效應的改變有關，新產生與消失的吸收峰，推測為界面所引起。
　　SmBaMn2O6單晶的室溫吸收光譜顯示有三個主要的吸收峰：1.3 eV、3.4 eV及4.2 eV，第一個對應Mn3+ d_(3x^2-r^2 ) 或d_(3y^2-r^2 )→鄰近Mn4+ d軌域之電子躍遷，第二、三個對應O 2p→Mn 3d軌域之電子躍遷。樣品在溫度高於電荷軌道有序轉為無序之相變溫度(TCO1, 370 K)時，X光繞射實驗顯示Jahn-Teller效應減緩，導致d-d電子躍遷能量減小。SmBaMn2O6的拉曼散射光譜有4個主要拉曼峰：196 cm-1、330 cm-1、485 cm-1及614 cm-1，分別為旋轉1、旋轉2、Jahn-Teller扭曲及呼吸振動模，旋轉1及呼吸振動模在溫度高於330 K時消失；溫度低於電荷軌道有序態之相變溫度(TCO2, 200 K)時，Jahn-Teller扭曲及呼吸振動模皆分裂成兩個峰，且整個頻譜多了許多新的拉曼峰，表示有強烈的電荷-軌道耦合及超晶格的產生。

關鍵字

Nd0.35Sr0.65MnO3 ； YBa2Cu3O7 ； Nd0.35Sr0.65MnO3/YBa2Cu3O7 ； SmBaMn2O6 ； 橢圓偏振光譜 ； 拉曼散射光譜

並列摘要

We studied the optical properties of perovskite Nd0.35Sr0.65MnO3　(30 nm) (NSMO)、YBa2Cu3O7　(40 nm) (YBCO)、NSMO (30 nm)/YBCO (30 nm)heterostructure thin films and double-perovskite SmBaMn2O6 single crystal.We employed the spectroscopic ellipsometry to investigate the optical constants and electronic structures of these materials. Furthermore, we performed Raman scattering study of SmBaMn2O6. The analysis of the temperature evolution of lattice vibrational modes would give important information about lattice-charge-spin interactions.
Room temperature optical conductivity spectrum of NSMO determined from spectroscopic ellipsometry analysis shows two main bands at about 1.1 eV and 3.7 eV. The absorption peaks of 1.1 eV and 3.7 eV are due to Mn3+ d → its neighbor Mn4+ d and O 2p → Mn 3d charge-transfer transitions, respectively. The optical conductivity spectrum of YBCO determined from spectroscopic ellipsometry analysis shows three main bands at about 3.1 eV, 3.8 eV and 4.6 eV. The 3.1 eV absorption peak is due to charge-transfer transitions between O 2p and Cu 3d states. The 3.8 and 4.6 eV absorption peaks are due to charge-transfer transitions between Cu(1)3d_(3z^2-r^2 )and4p_x. The optical conductivity spectra of NSMO/YBCO heterostructure show changes of the peak position and intensity in comparison with those of the single layers, indicating that strain effect of heterostructure modifies the electronic structures of individual NSMO and YBCO layers. The observed new absorption peaks are possibly due to interface-induced effect.
Room temperature absorption spectrum of SmBaMn2O6 determined from spectroscopic ellipsometry analysis shows three main bands at about 1.3, 3.4 and 4.2 eV. The first absorption peak is due to Mn3+ d_(3x^2-r^2 ) (or d_(3y^2-r^2 ))→ its neighbor Mn4+ d. The second and third peaks are due to O 2p →Mn 3d charge-transfer transitions. Their positions show redshift at the charge-orbital order-disorder phase transition temperature (TCO1, 370 K). X-ray diffraction data show J-T distortions relax, resulting in a redshift of d-d transitions be lower. Room temperature Raman scattering spectrum of SmBaMn2O6 exhibits four phonon modes at about 196 cm-1, 330 cm-1, 485 cm-1, and 614 cm-1 attributed to the rotationlike mode 1, rotationlike mode 2, Jahn-Teller mode and breathing mode. With increasing temperature, rotationlike mode 1 and breathing mode disappear above 330 K. Jahn-Teller mode and breathing mode show a splitting and many vibrational modes appear below charge-orbital order phase transitiontemperature (TCO2, 200 K), suggesting the strong charge-orbital coupling and the appearance of superstructure.

並列關鍵字

Nd0.35Sr0.65MnO3 ； YBa2Cu3O7 ； Nd0.35Sr0.65MnO3/YBa2Cu3O7 ； SmBaMn2O6 ； spectroscopic ellipsometry ； Raman scattering

參考文獻

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