Development of high-energy resolution photoemission spectrometer and study of the electronic structure near the Fermi level

我们在东北大学建造了一台高能量分辨率的光电子能谱仪，它有一个直径300毫米的半球电子能量分析器和一个高亮度的放电灯。该光谱仪的基压小于2x10^-11；Torr。使用闭合循环氦低温恒温器将样品冷却到8K。我们已经达到了大约12 meV的能量分辨率，与世界纪录处于同一水平。利用这台光电子能谱仪，我们研究了各种有趣的物质和现象，如下所示。1.直接观测Bi_2Sr_2CaCu_2O_8高温超导体的超导带隙及其各向异性和Dx^2-y^2对称性。2.在非铜酸盐层状钙钛矿超导体Sr_2RuO_4中观察到扩展的van-Hove奇异性(VHS)，这与在铜酸盐高T_c超导体中观察到的扩展VHS非常相似。3.首次直接观测到CEB_6.4中晶场分裂产生的卫星结构。一价铈化合物的磁性相变研究。首次直接观测到CESb的费米面拓扑随磁相变的变化。5.直接识别UPD_2Al_3.6中E_F附近的定域和巡游5f态及其温度变化。准一维有机导体DCNQI-Cu的Peierls带隙观测和E_F.7附近电子态的Tomonaga-Luttinger特征的鉴定首次直接观测到磁铁矿Fe_3O_4中由于Verwey转变而产生的能隙。

We have constructed a high-energy resolution photoemission spectrometer at Tohoku University, which has a 300-mm-in-diameter hemispherical electron energy analyzer and a highly bright discharging lamp. The base pressure of the spectrometer is less than 2x10^<-11> Torr. The sample is cooled down to 8 K using a closed-cycle He cryostat. We have achieved the energy-resolution of about 12 meV,which is on the same level of the world record. With this photoemission spectrometer, we have investigated various interesting materials and phenomena as shown in the following. 1. Direct observation of superconducing gap and its anisotropy in Bi_2Sr_2CaCu_2O_8 high-Tc superconductor and identification of the dx^2-y^2 symmetry. 2. Observation of an extended van-Hove sigularity (VHS) in a non-cuprate layred perovskite superconductor Sr_2RuO_4, which is quite similar to the extended VHSs observed in cuprate high-Tc superconductors. 3. First direct observation of a satellite structure due to the crystal-field splitting in CeB_6.4. Study of the magnetic phase transition of cerium monopnictides. The first direct observation of the change of the Fermi surface topology of CeSb accompanied by the magnetic phase transition. 5. Direct identification of localized and itinerant 5f states near E_F and its temperature variation in UPd_2Al_3.6. Observation of a Peierls gap of a quasi-1D organic conductor DCNQI-Cu and identification of the Tomonaga-Luttinger character of the electronic states near E_F.7. First direct observation of an energy gap in magnetite Fe_3O_4 due to the Verwey transition.