教師資料查詢 | 類別: 研究報告 | 教師: 杜昭宏 Chao-hung Du (瀏覽個人網頁)

標題:過渡金屬硫化物及氧化物的物理特性之研究---子計畫四---同步輻射X光散射之過渡金屬硫化物及氧化物的電子結構與磁結構之研究
學年97
學期1
出版(發表)日期2009/01/01
作品名稱過渡金屬硫化物及氧化物的物理特性之研究---子計畫四---同步輻射X光散射之過渡金屬硫化物及氧化物的電子結構與磁結構之研究
作品名稱(其他語言)Study of Electronic and Magnetic Structures of Transition Metal Sulfides and Oxides Using Synchrotron X-Ray Scattering
著者杜昭宏
單位淡江大學物理學系
描述計畫編號:{6};研究期間200908~201007;研究經費1,974,000
委託單位行政院國家科學委員會
摘要此計畫主要是要使用X-光磁散射及X-非彈性散射來探討過渡金屬硫化物NiS2-xSe2及過渡金屬氧化物La2-xSrxNiO4之電子結構及磁結構‧對硫化物系統我們計劃使用非彈性散射來研究其電子結構,並且使用X-磁散射來研究此系統的frustrated magnetism及電子自旋及軌道磁化密度間的耦合情形‧此外,此計畫也要使用高解析度的X-光散射來探討在強關聯繫統中由電荷密度所形成的有序排列結構的動態電子行為‧ 過渡金屬硫化物NiS2-xSex會隨著參雜量x的增加而產生一個金屬-絕緣體的相變化, 也被歸類為具有Mott轉變的物質‧此硫化物也具有一個複雜且豐富的相圖,此複雜性主要來自於電荷、電子自旋、電子軌道、及晶格之間的交互作用‧已有各種的理論及實驗數據被提出來解釋此硫化物的異常相變行為,但還是存在著許多疑點;如隨著參雜Se而產生的narrow band行為就不能以現有的能帶(band theory)理論來解釋‧本計劃就是要以較高能量的X光非彈性散射來研究此系統的電子結構‧除了對電子結構的研究外,也要使用X光磁散射來探討由Ni的電子自旋所產生的磁結構與晶格形變的關連性‧結合X光非彈性散射及X光磁散射的研究,本計劃希望能得到一個更詳細且更準確的物理數據來解釋此系統的複雜物理行為‧ 本計劃另一個要研究的主題是要探討在強關聯電子系統中由電荷密度所形成的有序條狀結構(charge ordered stripes)的動態行為。在強關聯繫統中很多的異常物理現象都是在參雜效應中發現的,如高溫超導cuprates 和與其相關的同相異構物La2-xSrxNiO4。在La2-xSrxNiO4中以Sr來取代La,在NiO面上會產生由電荷密度所形成的有序條狀結構。這些由電荷及電子自旋所形的條狀結構,已知在強關聯電子系統中的傳輸行為上扮演一個很中重要的角色。先前使用高解析度的X光散射,在La5/3Sr1/3NiO4中,我們發現這些條狀結構在相變點附近,可能是以所謂的電荷液體態(charge liquid)存在的。為了更進一步瞭解電荷液體態的物理行為,及其所形成的有序條狀結構的動態行為,我們計劃要使用高解析度的X光散射來研究這些電荷液體態在外加場(電流、電場)下的物理行為。 This proposal aims to investigate the electronic and magnetic structures of the transition metal sulfides NiS2-xSe2 and the transition metal oxides La2-xSrxNiO4 using various probes including the magnetic x-ray scattering and inelastic x-ray scattering. For the Ni-disulfides, we plan to study its electronic structures using inelastic x-ray scattering, and using magnetic x-ray scattering to study the frustrated magnetism and the coupling between the spin and orbital magnetization densities. As for the Ni-oxides, we will focus on the study of the dynamic behaviour of the charge stripes using high-resolution x-ray scattering under the application of driving forces (currents and electric fields). Pyrite-type NiS2-xSex undergoes an insulator-metal transition with increasing x, and is classified as the Mott transition. It also shows a complicated and rich phase diagram, and the complexity is mainly caused by the interplays between the degrees of freedom of charge, spin and lattice as that commonly observed in the strongly correlated electron system. By means of various probes, such as photoemission, magnetic susceptibility and heat-capacity, many models have been proposed to explain the metal-insulator transition. However, there still many puzzles remain, for example, the appearance of the narrow band with substitution of Se can not be explained by band theory, and the carrier number decreases in going from the paramagnetic insulating phase to the antiferromagnetic metallic phase in NiS1.5Se0.5. On the other hand, although the photoemission spectra have provided the features of the band structures, it can not provide a clear feature of the bulk property because of the surface sensitivity of the probe. With the use of hard x-ray inelastic scattering, we will be able to probe the bulk property, and give a deep insight into the understanding of the metal-insulator transition in this system. In addition, NiS2-xSex possesses a rather simple crystal structure but a complicated magnetic structures at low temperatures, for instance, the parent compound NiS2 undergoes a transition to become an antiferromagnetic insulator at T~ 40 K, but its degenerate energy levels are further left by a small lattice distortion at T~ 30K, and then becomes a canted antiferromagnetic state. The use of magnetic x-ray scattering will allow us to study of magnetic structures and the coupling between the spin and orbital magnetization densities in detail. As for the cuprates related compound La2-xSrxNiO4, the substitutions of La with Sr provide hole carriers, and the doped holes tend to order in a stripe-like structure acting as domain walls within the NiO2 planes; namely charge stripes. The interplay between this ordered state and the spins of Ni dominates the transport behavior at low temperatures. Transport and optical conductivity measurements have demonstrated the anomalous phenomena resulting from the formation of the charge stripes, in particular a pronounced change in conductivity has been observed in La5/3Sr1/3NiO4. Using high-resolution x-ray scattering, we demonstrated that the charge stripes possess the two-dimensional characteristic in nature and quasi-long range order at low temperature. Such a disordered state suggested the possible existence of charge liquid state around the transition temperature. In order to further study this fascinating charge liquid phases, I intend to investigate the charge stripes how to behave under the application of driving forces (current and electric fields) using high-resolution synchrotron x-ray scattering.
關鍵字X光磁散射; X光非彈性散射; 電子結構; 磁結構; 電荷液體態; 相變; magnetic x-ray scattering; inelastic x-ray scattering; electronic structure; magnetic structure; electronic liquid phase; phase transition
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