- 學位論文
第一原理計算研究亞鐵磁Eu2MnSi2O7之磁光效應及二階非線性光學性質
Ab Initio Studies of Magneto-optical Effects and Second Order Nonlinear Optical Effects in Ferrimagnetic Eu2MnSi2O7
摘要
在固體中，有趣且有用的物理現象基於對稱性。新的亞鐵磁性結構銪黃長石型氧化物Eu2MnSi2O7半導體破壞了空間反演(P)、時間反轉(T)和PT對稱性，因此產生了磁光效應，以及由光產生的體光伏效應(BPVE)和二次諧波生成(SHG)等二階非線性光學效應。 在本論文中，我們基於密度泛函理論和廣義梯度近似加上局部庫倫排斥方案，對於線性光學效應、體光伏效應(BPVE)和二次諧波生成的光學和磁光學性質進行了詳細的理論研究。我們發現，磁光克爾旋轉角在光子能量~3.24 eV和~4.02 eV處達到顯著峰值3.73°和-3.83°，並且磁光法拉第旋轉角在光子能量區域(~3.4 eV到~3.9 eV)，(~5.4 eV到~5.5 eV)和(~6.4 eV到~6.8 eV)到達近乎50°/μm。 對於二階非線性光學部分，我們發現，相比其他三種BPVE電流，圓偏振光注入電流在光子能量~5.7 eV處達到相對較大的顯著峰值~250 (μA/V^2)。 對於二次諧波生成，由於材料中的大磁矩，計算顯示了i型和c型電偶極SHG (ED-SHG)值有相同尺度。在特定實驗設置下，兩種ED-SHG類型的干涉也顯示出巨大的SHG強度變化，並且在SHG光子能量區域2.62 eV到2.7 eV中，此計算提供了在最近的一項實驗中探索藉由改變磁場方向，SHG和MSHG的強烈干涉效應的有力證據。
並列摘要
In a solid, the interesting and useful physical phenomenon is based on the symmetry. The new europium melilite-type oxide Eu2MnSi2O7 semiconductor with ferrimagnetic structure breaks the spatial inversion (P), time-reversal (T) and PT symmetries, thus leading to the MO effect and the second order optical effects such as bulk photovoltaic effect (BPVE) and second harnomic generation (SHG) generated by light. In this thesis, we present a detailed theoretical study of the optical and magneto-optical properties for linear optical effects as well as bulk photovoltaic effect (BPVE) and second harnomic generation for second-order nonlinear optical effect, based on the density functional theory with the generalized gradient approximation plus onsite Coulomb repulsion scheme. We find that the MO Kerr rotation angles reach the significant peaks 3.73° and -3.83° at photon energy ~3.24 eV and ~4.02 eV, respectively, and also the MO Faraday rotation angles display near 50°/μm) at the photon energy region (~3.4 eV to ~3.9 eV), (~5.4 eV to ~5.5 eV) and (~6.4 eV to ~6.8 eV). For the second order nonlinear part, we find that the circular injection current reaches the relative larger significant peak of ~250 (μA/V^2) at photon energy ~5.7 eV compared with others three type of BPVE current. For the second harmonic generation, the calculations display the same scale of both i-type and c-type electric-dipole SHG (ED-SHG) due to the large magnetic moments. The strong SHG intensity difference by the interference between the two type ED-SHG also is shown at the SHG photon energy region 2.62 eV to 2.7 eV with the specific experimental setup, which is the strong evidence in the recent experiment for exploring the strong SHG interference between crystal structure-induced SHG and magnetization-induced SHG (MSHG) by switching magnetic filed in the ferrimagnetic Eu2MnSi2O7.